Honda-SOHC
SOHC.co.uk Forums => Other Bikes => Topic started by: neildavies67 on September 09, 2017, 11:51:05 AM
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Hi folks! What do people think? Is this cylinder head salvageable? If so, can someone reccomend a decent engineer? If not, does anyone have a cylinder head for sale to fit a 1969 Honda CL350 money pit? Cheers!
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I bet that sounded nice when it went tit's up!
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One for Trigger but looks a bit toast to me.
I probably have a full head spare but I hate parting with my 250/350 stuff (I believe the heads are the same). DK obviously have them but at a high price ..
If you don't get fixed up I will see what I have but I wouldn't have a clue what to charge.
http://www.ebay.co.uk/itm/Honda-CB350K-CB350-K-1968-1974-Track-Bike-Project-Engine-Cylinder-Head-Valves-/311924609758?hash=item48a027d2de:g:UrUAAOSwrk5ZeF5c
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Cheers AshimotoK0! I've fired off some e-mails and pics to some engineering firms so will wait and see what comes back! There are a few videos on YouTube showing combustion chamber repair by welding extra material and re-machining so I am "glass half full" at the moment! I will update as soon as I receive some replies!
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I bet that sounded nice when it went tit's up!
I wouldn't know (although I wish I had known). I bought this beast as is (a non-runner with reasonable copression)! I gambled and am now paying the price! I haven't given up on it yet though!!!
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Checked and all the spare heads I have are for CB250's and the 350 has a different part number with a ---287--- centre part no. Lots cheap in the States but not a lot on eBay here. YOu could ask on Hondatwins.net if anyone in Europe has one to sell. I think any year would fit fine . 'Outobie' on there is the guy to ask.
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See this:
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Cheers for looking AshimotoK0. I'm going to hold fire until I get some responses from my engineering enquiries! Exhaust studs are 8mm. I'm off to drown my sorrows now! Cheers again for the assistance.
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That was a top ring shattering and exiting the ring groove whilst wrecking the piston.
used to happen a lot if owner thrashed bike from cold
Less bad ones would just rebore and replace pistons and not worry about head
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Hi folks! What do people think? Is this cylinder head salvageable? If so, can someone reccomend a decent engineer? If not, does anyone have a cylinder head for sale to fit a 1969 Honda CL350 money pit? Cheers!
I would look for another head, it will be a money pit if it needs new valves, valve seats and valve stems.
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Neither the head or the piston seem to have that classic imprint of broken rings having been embedded into the metal, from what I can see in these photos or the other thread with the piston pics included.
It looks more like detonation as the marks / pitting are soft and look more moth eaten metal than mechanical impact.
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I think there has been something in the bore possibly some spark plug parts, whatever it was the head is toast, me i would go for another head.
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They will do well if they can repair that with weld without distorting the head. I wouldn't have thought it would be cost effective to repair compared to finding a good second hand head.
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Thanks to everyone for their comments and advice! The consensus appears to be leaning towards"shagged". That's depressing but it is what it is! I agree with K2-K6 though, I haven't found any indication of mechanical damage, just the pitting. I would have thought that if there had been a stray piece of piston ring or plug in there at some point there would be more damage. Doesn't matter either way though I suppose, still shagged! I'm going to carry on drinking while I can still afford it! Thanks again everyone! :(
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I would be tempted to sort the valve seats and dress the damage carefully with a dremel. I don't think it will make a jot of difference, you wont be racing it no doubt. Others may think different but it is your money. :)
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I don't feel its a disaster. From a simple build the engine from parts point of view, then it's logical to go with the opinion of needing another part to replace it. I don't disagree with that.
From a straight engineering and materials point of view its not really a big task and if it were, or is, a rare part then you'd go with a repair.
Toward that view, I'd put valves and plugs back in it to facilitate a localised blasting of that combustion chamber (maybe you could interest Ash into help with that part) this would need to be done to remove all traces of carbon and contaminants from the damage site. Ideally, you'd heat the head prior to Tig welding for building up the damaged area prior to letting it cool slowly which should avoid distortion. You need to blast it clean to avoid any inclusions in the weld material, and then the inert gas should prevent problems.
Afterwards, skim it lightly to bring the surface back and finally dress out the combustion chamber shape with abrasive on dremmel to match the squish shape to the good one.
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I am wondering what the actual difference between the 250 & 350 heads are because the valves and guides are certainly the same p/nos. Can you measure the width of the head dome .. I do have a 350 head from my K1 I could measure but it's buried at the mo'. 'Florence' on here may have 350 head spare .... faint possibly ... worth an ask.
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I would be tempted to sort the valve seats and dress the damage carefully with a dremel. I don't think it will make a jot of difference, you wont be racing it no doubt. Others may think different but it is your money. :)
+1
I've cleaned up and re-used worse heads
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On my first big bike, a cb550k3 I found the head to be in similar shape when deciding to sort out a really bad oil leak, on mine the top piston ring was AWOL, on every piston, having exited taking a fair bit of the top of the piston with it. I was due to go on a holiday to Scotland with a mate in a days time so bunged on a decent used set of piston and barrels I had and bolted it all back together after a fairly cursory job of de blurring the chewed up head and grinding the valve seats with 2 grades of valve paste. The bike was up and running with 9 hours to spare before the holiday and ran brilliantly for the week and quite some time after. Eventually a nasty cheap O ring between the head and barrels either melted or swelled in the oil, either way it blocked the oilway and that killed it - never actually broke down, but the rattle was alarming so it got retired, but before that the bike ran fine despite having a head in similar wrecked shape. At least with an imperfect repair you can ride the bike gently, knowing you need to look out for a spare engine or head. On my bike that worked out ok, I found a engine for not very much money that had been by the look of it stored in a canal, bottom end very dead from corrosion, top end very well preserved in oily sludge, beast journal bearings I've seen out of about 15 cb550 top ends.
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I do have a spare but they are so hard to come by I would have to be very convinced monentarily.
The difference between the 250 and 350 head? The 350 head has a slightly different combustion chamber shape which corresponds with the different bore size. I think it would be possible to have someone grind the material away from a 250 head to make it the same.
How about this, good price I would say:
http://www.ebay.co.uk/itm/Honda-CB350-CB-350-1971-1972-1973-1974-1975-Engine-Cylinder-Head-/311822638588?hash=item489a13ddfc:g:BZsAAOSwol5YxsHb
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In the eighties I rode one of these things every day, even touring abroad (What was I thinking?).
I once had the choke mechanism go into the bore on my 350. The metal over time can become brittle so worth a careful inspection each time you have the carbs off. I have seen some chokes with small amounts missing which probably went in without anyone noticing. In this case the whole half of the choke came off including the sprung steel bit which lets air in when choke fully closed. I have also seen carbs with one of the throttle screws missing. Judging by the damage on yours, I think that may have happened, I can make out a thread mark in on of the collision sites. Again worth checking when you have them apart. The vibration from these machines makes everything fall off eventually. They are great little bikes but need a bit of care. I even had a silencer fall off. I was very lucky, it hit the rear tyre and flew over a hedge.
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I probably do have a spare 250 one (or two) and to hang onto it would just be hoarding. Could be tempted to part with it for 50% of what DK are asking but would need to check it out first. Otherwise I would rather hang on to it as Florence rightly says.
Seems from other knowledgeable guys on here though that fettling of yours is not out of the question. I can bead blast it for free for you but that would mean post both ways for you.
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when I had the choke go into the bore I managed to clean up the combustion chamber with hand tools. It wasn't as bad as yours but the valve surface looks intact which is encouraging. My one which looked pretty nasty even after tidying up ran absolutely fine and I soon forgot all about it.
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I know what you experienced Florence, a friend had two of those sluice type choke flaps go through the motor on a 750 K6. One went unnoticed but the other flattened the spark plug gap and the cylinder stopped firing. When the head came off there were barely noticeable marks on piston and head, I was really surprised that there was not more significant visible damage.
The reason I think it's detonation ( obviously I'm looking at the photos) is that the aluminium craters have soft melted edges which just doesn't happen with physical assault but only with heat conditions in the combustion chamber. It appears there are no marks up in the top of the cylinder head either, the damage is confined to the squish area of the head material and this is likely to run hotter than the crown.
It's an interesting case as it appears to have been stopped from running part way through a failure process. The next thing that would have happened is the piston ring lands would start to dissappear, only then are the rings usually released and impact both the piston crown plus head. When that eventuality is taken apart then the rings are often pointed to as the culprit of failure. It's an important point that the chronology is the other way round in that the detonation came first as the route cause, which then consequently trashed the piston rings once they could no longer be held in place.
It's not often that four stroke piston rings fail on their own with all other things being intact first. It's obviously important to ascertain the true cause else you run the risk of a repeat once rebuilt.
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Wow, lots of advice for me to mull over! Thanks everyone, feeling much more positive this morning! My current plan is as follows: purchase cheap compressor (hopefully second hand to save cash) and soda/walnut shell blast the crap out of the head to remove carbon. I need to clean up all the other engine cases and various other bits and pieces so I can (kind of) offset the cost against time I would otherwise have spent doing it all by hand. Hopefully get a response from one of my enquiries re: combustion chamber repair, that doesn't cost mega bucks! Otherwise it's Dremel time as suggested! While I'm spending the kids inheritance, I intend to get the valve seats done, rebore, pistons & rings, cam chain and tensioner. By the time I've got the camshaft and followers done with Boyer Bransden ignition, apart from having spent stupid money which I'll never get back, hopefully whatever caused the problem in the first place wont raise its head again (but my wife may have left me!). Out of interest, the depth of the chamber is 20.3 mm, 64 mm diam with a 30 degree chamfer 4.5 mm wide. All measurements very approximate! How does that compare with the 250 head AshimotoK0? If they could be machined to match the 350 chamber dimensions, I would certainly be interested in taking one off your hands if you're happy to part with one. Thanks for the link Florence, that certainly looks like a good head relative to mine! Does anyone know if the heads are exchangeable across all the models (except the camshaft housing)? It's wierd that the add seems to indicate '71 onwards. I notice the head is stamped M 10, mine is stamped E 2. Is that significant? Once again, many thanks for all the advice and optimism. The body and mind are willing but the wallet is getting rapidly empty!
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Well it seems they are prone to trauma. I dug this 250 spare one out (not one I had reserved for my bikes I am restoring) and some strange marks particularly the almost perfectly semi-spherical indent. I think it came from an engine in bits I bought that had some NOS parts from DS (tensioners etc) that came with it (K4 engine) that I wanted badly. PS DO NOT buy any cruzinimage tensioners for this engine ...you have been warned !! The genuine main tensioner is mega expensive ..even though the roller in it is exactly the same as the 750 one which is much cheaper. So the temptation is natural to use pattern but DONT . Here it is (t used to be £63plus VAT but actually come down a bit recently) http://www.davidsilverspares.co.uk/CB350K0-SUPER-SPORT-1968---1969/part_2990/
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That one above looks definitely as if the cylinder has ingested something, there's a huge difference between that one and the original subject. Also more pronounced damage up in the centre where something has rattled around.
They are quite a radical spec when you look at the numbers they run. About 110bhp per liter capacity, that's a lot for a two valve engine even today. That 285 cam would also be quite hefty in a car engine with just marginal tickover stability, reasonable torque spread plus higher rpm flow. Usually known as a rally / mild race grind.
I'd guess from the rpm range, compression ratio, cam timing etc you've got to be fairly diligent in setting up these twins to really get them running spot on.
My perception in reading other info about them is that cam problems seem to crop up a fair amount, what would others see?
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That one above looks definitely as if the cylinder has ingested something, there's a huge difference between that one and the original subject. Also more pronounced damage up in the centre where something has rattled around.
They are quite a radical spec when you look at the numbers they run. About 110bhp per liter capacity, that's a lot for a two valve engine even today. That 285 cam would also be quite hefty in a car engine with just marginal tickover stability, reasonable torque spread plus higher rpm flow. Usually known as a rally / mild race grind.
I'd guess from the rpm range, compression ratio, cam timing etc you've got to be fairly diligent in setting up these twins to really get them running spot on.
My perception in reading other info about them is that cam problems seem to crop up a fair amount, what would others see?
Agree .. I have seen engines particularly from the States that have done miniscule mileages (typically 5k) but the fat cam (286) has pitted lobes. I am sick of people , particularly on the likes of FB, saying that the '68 250SS (K0) was merely a "learner / ride-to work hack'. Hardy .. for a 4-stroke 250cc to develop a quoted 30 BHP in 1968 was going some in my book. Even comparing 2-strokes The Suzuki Super 6 250 was 29 BHP , later Hustler 33 BHP and Kawasaki Samurai 250 was 31. BTW ..one for Trigg ... the Samurai had Cdi ignition in 1969 !
I remember my mate at school flogged me his '68 CD175A 'sloper' as he just bought a TR25W (Triumph Trophy 250cc =22 BHP) .. a choice he kinda regretted forever after.
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It's hard to find even modern cars that are considered quote radical that don't reach the specific output of these engines, and they use 4 valve heads along with fully mapped fuel injection and ignition. These old bikes are really quite remarkable in engineering terms.
The camshaft wear problems I feel are mostly related to setting the clearance really accurately, and maintaining it. If you loose the clearance of the rocker to cam base circle then you effectively deprive the whole cam lobe of any sensible lubrication. They are a fairly simple system that dips the cam into oil generally of engines that have the rocker above the cam. The clearance allows the oil to pass as a film onto the rocker pad. If you remove the clearance, then you effectively squeegee the oil off the cam with the rocker around its entire circumference. What would normally be a resupply before each time the cam peak reaches maximum pressure and loading fails to happen. The cam and the rocker then effectively cold weld parts of each face together which results in pulling both of them apart in a fairly short time frame.
Notice how on that Dutch 450 of Jensen's he is hyper diligent with tappet clearance, he even, I think I recall, runs them slightly wider during early stages. That's a very important part of his success I believe.
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The head I have that is damaged I would possibly clean up and use if I didn't have others that are much better... centre damage isn't that bad really when you see it in the flesh.
See this old 750 SB ... seems it wasn't just bits in the carbs that found themselves in the engines ;)
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Well I rest my case your honour.
I posted a question on HondaTwins for you ..Loads of views but no comments...zilch ...then it usually disappears off the radar. Compare the response on here and you can see why this site is so much better than the others. I have 'bumped' it so that may jar/shame someone into action ..... but it's a fairly basic question ..... there must be someone on there with an opinion/advice. I know the CB250K was not sold in the States but there are lot of members on there from Europe, NZ and Australia, where they did sell the 250 version in large numbers. This isn't a one off either .... I have had the same with requests for advice on my CD125, CB72 & 450K0 bomber twins ..very little or no response. Have to say you do get a fantastic response on the dedicated CB72/77 Facebook group though, as much as I hate Social Media sites.
http://www.hondatwins.net/forums/48-engine-discussion/94745-differences-cb350k-vs-cb250-cylinder-heads.html
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You may not get an answer on Hondatwins but you certainly get a lot of retail opportunities. Stephen from Glasgow doesn't have to hide his feet anymore thanks to fungal nail treatment, and 1000's of people from my town are taking advantage of a new funeral policy, who knew?
Another reason to donate here, so we don't have to wade through mountains of such crap.
That said, I know nowt about Honda twins, other than the fact that in a straight drag race on a deserted industrial estate, my mate's Candy Gold CB250 easily beat my BSA A7SS.
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I am beginning to suspect that the head in my picture is in fact a 350K one not a 250k..... I am going to my 'stash' tonight to dig out what I know is deffo a CB250UK one from a 5k mile UK bike.
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It's conceivable that they use the same head for both, what is the bore difference between the two?
If for example you put a 350 head onto a 250 size piston at the design stage you'd loose compression ratio as you have less swept volume going into same sized combustion chamber. It's fairly common to adjust compression ratio with a higher or lower piston crown shape, so there's the possibility that they did this. Worth comparing the two types of piston to see what they tell you as well.
Or they could have done it the opposite way with 250 capacity enlarged to 350 then used lower piston crown to get compression back to where they wanted. This would give more squish band to the 350 which wouldn't be a bad thing and may allow the two to run at the same timing setup.
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Well I cocked that one up. My head picture I posted was from a Cb350K1 and I think I know what the cause of the trauma on it was. I got the bike from DK with 10k miles but with weather seized engine. When I stripped it the engine was in really nice condition (inc cam and followers) but surprisingly had +0.25mm 1st overbore genuine Honda pistons. The engine was not in fact weather seized...I found a large mangled split pin jamming the primary drive gears.
This picture below is deffo a CB250K0 head that was taken from a 1969 Reg. left in a garden to rust with only just less than 6k miles on it that I 'found' end of last year. Note the lack of chamfer compared with the two CB350 pics. of heads. I reckon that the chamfer is the difference between 250 & 350K heads. I did have a K2 with Read Titan 325cc conversion in the 70's though which used the CB250K head and special Hepolite pistons & rings.
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They look like the same design from the photos, the 350 M4 just looks like a tidied up iteration of the casting mold.
It makes sense to chamfer the 350 squish area as it would keep the compression in the design range. I guess if they cast the 250 piston with a bit more meat on it and conversely the 350 version a bit less, then they may even be able to use the same crank and balanced spec for both motors. I've not seen the rest but it just looks like the 350 is really a mildly stretched 250 rather than a motor in its own right.
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Here's something interesting, an ebay listing for a new CB250 head K0-K4 but notice in the pics that the chamfer is present, unlike AshimotoK0's head - https://www.ebay.co.uk/p/Cylinder-Head-Honda-Cb250-K0-k4-B4-Cl250k-Part-NOS/605341165
I make the diameter on mine (excluding chamfer) about the same as AshimotoK0's 250 head. Have you measured the depth? Statfold engineering have said that they would have a go at making good my cylinder head but I might look out for a good condition 250 head first! It seems a lot easier to just machine a chamfer than make good on a chamber with a resemblance to the lunar surface!
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Going on what we've looked at with Ash's examples, that does look like a 350 in those photos.
It would seem difficult to change the volume of the main chamber as the valve seats and their geometry dominate the shape to the point that it would require more fundamental design change to casting to achieve this. They just look like they trimmed volume with that taper and nothing more.
The usual means of measurement is to use a piece of perspex, grease the gasket surface to get a seal and place the perspex with a hole drilled through it over the combustion chamber. With valves and plugs installed you can run in something like diesel from a burrette to measure the real volume in cc's.
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Here's something interesting, an ebay listing for a new CB250 head K0-K4 but notice in the pics that the chamfer is present, unlike AshimotoK0's head - https://www.ebay.co.uk/p/Cylinder-Head-Honda-Cb250-K0-k4-B4-Cl250k-Part-NOS/605341165
I make the diameter on mine (excluding chamfer) about the same as AshimotoK0's 250 head. Have you measured the depth? Statfold engineering have said that they would have a go at making good my cylinder head but I might look out for a good condition 250 head first! It seems a lot easier to just machine a chamfer than make good on a chamber with a resemblance to the lunar surface!
I do have a 250K4 head so I will check if that has a chamfer but it's at my stash. Having said that I just checked a later CB250G5 head I have here and that does not have a chamfer and measures 56mm too and that engine uses the same piston part no. as the earlier K models.
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It looks to me that you'd need about 3.9cc larger volume in the 350 combustion chamber to maintain compression, at a rough calculation. If you spread that between piston crown and chamfer volume then it's not that much material.
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Ash, your first head picture is 350 and second 250. I think the engine was designed as a 325 and then sleeved down to a 249. The heads are the same apart from the squish area. One of my 250s had a crankcase which fits the 325 barrel, later ones have smaller holes in the crankcase. Other than the bore and the squish area and conrods, the engines seem to be the same as one another.
This one, https://www.ebay.co.uk/p/Cylinder-Head-Honda-Cb250-K0-k4-B4-Cl250k-Part-NOS/605341165 is a 350 head despite what the advert says.
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It looks to me that you'd need about 3.9cc larger volume in the 350 combustion chamber to maintain compression, at a rough calculation. If you spread that between piston crown and chamfer volume then it's not that much material.
I will measure the head volumes on both heads and report back ! Although the stroke is the same for 250cc & 350 (325cc) the big ends have more rollers in the 350 model.
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To extend what I've posted above, the total volume increase would be as stated ( loosely, 75cc extra capacity divided by two for cylinders swept volume, then divided by the compression ratio of 9.5).
There is also extra volume that can't be measured in the head shape, that is when you increase the bore size then the area above the periphery of the piston and the head plane also increases, so you'd have to subtract that from the total to get the true increase in volume for just the combustion chamber.
.........which would be the difference in volume of the two different bore sized discs with a thickness of the clearance of piston to head plane dimension, if that makes sense. I've got it going round in my head but it seems harder to write than think about!
It's obviously the combination of these two volumes that make the real difference to the engine.
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Worth an ask:-
https://www.gumtree.com/p/replacement-parts/honda-cb250-350-k4-engine-parts.-/1265551797
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I checked another head today from a CB250K4 and it was the same as the other 250 earlier head I pictured....i.e. with no chamfer 56mm dia.
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Given that the original problems with this engine are to be repaired it's always gutting if you get a repeat, especially as it's so difficult to readily get parts for some of the older examples.
With that in mind I thought I'd forward a discussion as to what went wrong in the first place as it appears to me to that there is a story within it waiting to be observed. It's trying to tell us something, I believe.
It's unusual that the previous owner seems to have stopped using it as the problems were building, which gives a fairly unique look at the problems before it blew itself to bits.
I'm maybe putting two and two together then coming up with five but think it's a plausible theory which may gather some further thoughts.
It looks like it's run with no valve clearance on the exhaust of the damaged cylinder. This has the effect of compromising the lubrication to that lobe (can't see the whole effect from the photos) . If it has, the cam wear is one consequence. The second path of effects could go as follows;- running with the exhaust valve slightly off its seat allows the valve head to go over temp as seat contact is critical to control heat build up. Also it allows compression to leak away just as it comes up to ignition event, this compromises the burn formation in that cylinder, which being incomplete, promotes carbon buildup in that chamber.
Here's where it comes together more, carbon buildup insulates the combustion temp from reaching the aluminium and so partly cuts off its transfer out to the fins for dissipation. This results in both a hot cylinder and a hot exhaust valve, probably above sensible operating temps that would normally be experienced.
Given these temps and some unburnt mixture are still present, this is exactly the conditions that propagate detonation. Commonly known as pinking or knock. As above, it's not often you see this stage as it usually, when run further, will take out the top land of the piston which let's the rings go. It's this mess that is usually found when the motor fails and someone takes it apart. The rings get the blame when often they were the last things hanging in there.
I feel that ultimately it's a story of no valve clearance causing a whole trail of problems from such a simple start point.