Honda-SOHC
SOHC.co.uk Forums => CB750 => Topic started by: yozzer74 on March 02, 2017, 10:22:03 AM
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Well I'm going to after take my engine back out the smoking is getting worse . The bike has only done 50 miles . I know I will have to change gaskets but will I have to buy new oil seals . Or can I reuse them . Any ideas on what I should look for when I get it apart as to why it's smoking . I will try get another video of the bike running to show the amount of smoke . I had the exhaust off number 1'3'4 had a lot of oil in the ports . Just to recap bike had new rings fitted and valve guides had valves recut and seats . Thanks yozzer
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https://youtu.be/FI0__SzOS7s
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Incorrect valve to guide clearance or bad stem seals is my guess
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In what way guides too big . When you put stem seals on do they just push on wondering if I haven't fitted them correctly.
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Dude proper gutted for you, I know exactly how that feels.
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I'm with Bryan given that its happening on 3 cylinders and with what you have replaced
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Seriously annoying that it's not possible to remove the head with the engine in the frame, but it does look as though your got oil leaking past the valves, if you get a mate involved though the engine will be out in less than a couple of hours, then assess the problem an hour or so, rebuild top end not a big job, engine back in a couple of hours, what I'm saying is it's a couple of weekends including waiting for parts, if you haven't got any mates (😄) I'll come and help you provided you're within 50 miles of Derby , PM me if you need a hand.
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What mark said. I know it's not a big help but I just did mine last week (I was a few hrs from turning it over when I found the issue) in just under three hours. Removed the lot then lifted the frame off the engine. On my own! I've got no friends.
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Lol no friends . I removed it on my own the first time . I'm sure I can rope some one in to give me a lift with it Hopefully . Just hoping it's not the bores that's the issue .
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This may help....
http://www.sohc.co.uk/index.php/topic,11851.msg90777.html#msg90777
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Depends who fitted the guides, if a car guy he will have given too much clearance for the valve stem
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It was a car guy who fitted them but if that was the issue would it not have smoked from the start . ??
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Hi Yozzer, just a thought but is it worth putting a few more miles on it before stripping?, it won't harm anything other than getting a bit of carbon build up perhaps, and you could get lucky and find that it's the rings that need further bedding in, that said it does look like a valve stem/seal issue but giving it another 100 miles of varied revs wouldn't take long, (that's if it will keep running without fouling the plugs of course), I'm just thinking that Pete said his smoked a lot until it bedded in.
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If its simply a valve guide, could you not use a compressor connected to the plug hole to hold the valve up, and do the job with the engine in with head on. Or the rope trick.
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If its simply a valve guide, could you not use a compressor connected to the plug hole to hold the valve up, and do the job with the engine in with head on. Or the rope trick.
I have done the rope trick before, certainly worth it just to check if the stem seals are on correctly.
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not if the valve guide has been reamed out too much, it would mean another replacement job
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Plus if the frame has not been modified the rocker cover cannot be removed with the engine in place.
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I keep seeing references to "the rope trick", to be honest I had no idea what it was so I've googled it, cmon guys how the heck is this going to help? 🙁
(http://i1269.photobucket.com/albums/jj582/POR1983/IMG_0582.png) (http://s1269.photobucket.com/user/POR1983/media/IMG_0582.png.html)
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It involves putting the cylinders you are working on to just before top dead centre, the stuffing rope through the spark plug hole, as much as you can get in, then turn the engine to top dead centre to crush the rope, then when you remove the valve springs the valves don't fall down as the top holds them up.
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Sorry, auto correct sucks, the ROPE holds them up
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It is possible to have the guides fitted with inserts instead of new guides but still needs the head off. SEP and The Cylinder Head Shop both do this. The diameter reamed should be 6.6mm I think. From experience car guys generally don't have the right gear. My local engineering shop will not touch valve guides on Japanese bike heads as they just don't have the right equipment and refuse to do a second rate job for some one.
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the rope trick only works on indians...
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Ha, excellent 😄
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Started taking engine out today after I had been out for a ride . Bike dropped on to 3 cylinders . When I got home took plug out of number one which was cold . Was caked in oil cleaned it up fired on all four again . I've got pipes off and carbs and I've had my fingers on valve guides and I'm sure I can turn them . ?? Will find out tomz my mate who was following me was also covered in oil lol
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That's a strip down then Yozzer, bad luck but hey it's all part of motorcycling!
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Well that's the engine out and stripped no obvious signs that I can see . I've taken barreles and head to machine shop to be measured and valves
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If there is any wobble between valve stem and guide the clearance is too big
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With how much oil it was chucking out yesterday I thought I would have found something
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Here's a thought .. are the breather pipes from the cases and rocker box all free of kinks etc and connected correctly.
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I haven't got the breathers connected .but I did put one of those k&n types on the breather from the head . And that's when my problems started so I removed it . But it carried on smoking .
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I've got one of those on mine, it looks horrible I keep meaning to remove it and fit a pipe that runs into a small catcher on the tail fairing, that said I've never know any oil to spit out, I take it you've checked the breather outlet is clear, million to one you introduced a blockage then you fitted the KN?, not very likely I know.
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Yeah checked it no blockage the breather that comes out of crank case should go to oil tank yes . I've just had a pipe coming off it there is quiet a bit of oil comes out of it is that normal ??
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Yeah checked it no blockage the breather that comes out of crank case should go to oil tank yes
that should be the gearbox breather (the thin pipe) . i can safely assume you have left the top engine breather and the oil tank breather to just hang down behind the battery(these are the thicker pipes} I have seen cases that people have mistakenly joined the engine breather to the oil tank that thens pressurizes the oil tank ? forcing oil out on to the back wheel very naughty ;)
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First F2 I had to do was doing 350 miles to the pint of oil with just the stem to guide clearance excessive that went to 150 miles per pint when 1 stem seal failed(all on the exhaust side!)
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Just got off phone with machine shop he says my bores are .75 over size he thinks I have the wrong size rings in can you get rings .75 over size he says looks like it's been rebored to that size ??
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Yozzer you should have took the engine to Steve he would have sorted it out properly..... Hopefully you will make it to CMC this year..... :o 8)
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I'm in contact with Steve he's helping me out with things on engine cheers
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I'm in contact with Steve he's helping me out with things on engine cheers
Nice one Yozzer, he is shit hot with that motor....
Ive not seen Steve for a while...remember me to him when you next speak
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I'm in contact with Steve he's helping me out with things on engine cheers
Nice one Yozzer, he is shit hot with that motor....
Ive not seen Steve for a while...remember me to him when you next speak
Is that Steve at Rotherham classics !
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It is yes
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Well found a few things out today when I rebuilt the engine I bought standard size rings as there were no markings on top of the pistons to say they were over size .they are also Honda pistons they have the number 410 on the side which I'm told is for f2 engine . But what I didn't notice was the number 75 on the side of pistons . In black ink which knowing what I know now means .75 over size so now I need to find some rings to fit the pistons anyone got any ideas were I could get some from David silvers hasn't got any [attachimg=1][attachimg=2][attachimg=3]
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Try Cruzinimage on ebay Yozzer
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Cheers Phil I will give them a try but I think I've tried them before for F2 they didn't have them
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Is that a crack i can see in the piston on photo No 3?
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It does look like that on pic. but it's not ;D
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Phew, that's good ;D ;D
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It does look like that on pic. but it's not ;D
Yozza try IMD pistons, I have had. Few bits from him.
Imd pistons.com
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Thanks I've sent them a email
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Thanks I've sent them a email
Yozza just seen these on eBay, any good item No 292063073922
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Thanks I've sent them a email
Yozza just seen these on eBay, any good item No 292063073922
K and F2 units have different pistons and rings ;)
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Any ideas trigger were I could get some cmsl have 3 sets in stock
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Any ideas trigger were I could get some cmsl have 3 sets in stock
If you can lay your hands on three sets 0+75, you can buy one set of 1.00 and grind them to spec. You must know what you are doing, to do this type of ring grind.
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Yeah the bloke at machine shop told me that . But he wasn't too sure about the oil rings
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Yeah the bloke at machine shop told me that . But he wasn't too sure about the oil rings
The oil rings just take longer to grind. Sometimes its the only way.
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Cheers good to know if I can't find another set
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Well I've managed to get three sets from cmsl and David silvers had just one set . David silvers said that the F2 had two different part numbers for the rings on the F2 so didn't know which pistons mine had does anyone know if the pistons are different or they just changed the part number .??
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This company does pistons and rings up to +4mm
http://www.scheuerlein-motorentechnik.de/motorrad/Honda/700-799-ccm-h7/cb750four-modelle/cb750f1/
Excellent quality, I used them on my F2, (they have them for Ks and F1s as well) I had the same oil burning problems went through 2 over size steps new guides etc, still burning, the cause eventuall found the machine shop boring he Barrells made the clearances too big, I did lots of research and consulted Hondaman (and his book) I insisted on this clearance, the shop said it would seize, and wrote a disclaimer. I got the clearance I needed, the bike ran perfectly, and never used as to of oil, oh and it didn't seize.!1
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Heres a similar link refererence 'Hondaman' info -
http://forums.sohc4.net/index.php?topic=89779.msg1005284#msg1005284
I used the recommended smaller clearance on my 836 cruzinimage big bore kit - 850 miles and so far so good. I am not sure what clearance the guy who bored my barrels used on my CR750 current build - he may have used the standard tolerences (I am now doubting myself whether I insisted on the smaaler clearance as I did on the last build) - time will tell when I start it up!
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This company does pistons and rings up to +4mm
http://www.scheuerlein-motorentechnik.de/motorrad/Honda/700-799-ccm-h7/cb750four-modelle/cb750f1/ (http://www.scheuerlein-motorentechnik.de/motorrad/Honda/700-799-ccm-h7/cb750four-modelle/cb750f1/)
Excellent quality, I used them on my F2, (they have them for Ks and F1s as well) I had the same oil burning problems went through 2 over size steps new guides etc, still burning, the cause eventuall found the machine shop boring he Barrells made the clearances too big, I did lots of research and consulted Hondaman (and his book) I insisted on this clearance, the shop said it would seize, and wrote a disclaimer. I got the clearance I needed, the bike ran perfectly, and never used as to of oil, oh and it didn't seize.!1
I agree. My 350F was left to the engineer to fix the boring size, just left him the barrels and 4 new pistons. Although he did a good job I am now thinking its going to need boring again. Smoking on two cylinders and using oil. I'm pretty sure he's bored it to a standard clearance as he's more used to doing British iron and that has about 5 thou clearance. What is the recommended clearance on a 350F, Hondaman recommends .0010" to .0012" but that's for the 750?
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0.0008-.0010 anything more then it will burn oil (that's what he recommends for the 750 and worked perfectly for me. I don't know the 350
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I had similar experience but the opposite way round, I had a Triumph Daytona (cast iron block) bored to fit new high compression Hepolite pistons, the borer did Jap bike tolerance of two thou when I'd asked for 5 thou, the engine seized!!.
A good borer will ask what clearance you want, the last bore job I had done was by Lancaster Engines, brilliant old school engineers.
http://www.lancasterengines.co.uk/classic-car-vintage-engine-reconditioning-services-in-lancaster/
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I had similar experience but the opposite way round, I had a Triumph Daytona (cast iron block) bored to fit new high compression Hepolite pistons, the borer did Jap bike tolerance of two thou when I'd asked for 5 thou, the engine seized!!.
A good borer will ask what clearance you want, the last bore job I had done was by Lancaster Engines, brilliant old school engineers.
http://www.lancasterengines.co.uk/classic-car-vintage-engine-reconditioning-services-in-lancaster/ (http://www.lancasterengines.co.uk/classic-car-vintage-engine-reconditioning-services-in-lancaster/)
I assume these guys are not the ones responsible for the seizure.
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Lancaster Engines, brilliant old school engineers.
Lancaster Engines are superb, no I have no connection to them before anyone asks. ;D They were extremely helpful when trying find oversize liners for my CB72/CL77 project racer.
I was a Toolmaker for 18 years and now a Mech Tech at a well known Pharmaceutical site for 18 years so appreciate proper engineers, which they are. The tight bore was done by a local motorcycle shop, in fairness it was an Ok job and probably would have worked well on a Jap engine but was not what I asked for. The Triumph engine nipped up within the first 1/2 mile of very gentle running, stripped and honed more by me and ran very gently for a long run in period, never nipping again.
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Thanks Tomb will give them a go. Quite handy really as I am only in Thornton-Cleveleys. Will pick a nice day and have a run over on the bike. Cheers.
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I'm in contact with Steve he's helping me out with things on engine cheers
Yozzer
I was over at Steve's place yesterday he said you had called a couple of times to asking for his help & advice, from what you told him about the work you had done, his thoughts were those who had done the rebore could have took too much out of the barrels, so he offered to try & get you a set of Barrels, which are hard to find, but he has now got a set, he spent some time sourcing them for you, but he tells me you have not been in touch since.
it made me feel a bit awkward because I put you in touch with him.
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No he told me he had some in shop that he's had for a few years and I could have a look if I needed them . I haven't had a rebore on my set of barreles so don't no why he would think that . We must have got our wires crossed .
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No he told me he had some in shop that he's had for a few years and I could have a look if I needed them . I haven't had a rebore on my set of barreles so don't no why he would think that . We must have got our wires crossed .
Yozzzer
I did think I had heard the story right but might have heard it slightly wrong its amazing how stories can vary though... :o
No worries on my part I was just trying to help in the first place thats why I put you onto Steve, I think in future I will keep my Nose out. :-[
I hope you get it sorted.
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Got engine back together and running https://youtu.be/zM9FyFWerNE
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sounds sweet
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Love it. Well done mate. Sounds superb. Is that a Yamiya Yoshi pipe?
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No James it's from carpys in the USA.
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Well done Yozzer! Back to normal now so 'on yer bike' this weekend - sounds great by the way
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Hope so Phil if weather picks up went out for a quick test ride tonight freezing
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Well done Yozzer, ready for the summer now.
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Looking and sounding good Yozzer.
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Sounds sweet :D
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Nice one dude.
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That's a really nice sound, good job
Cheers
Dennis