Oil pressure issue / motor rebuild

[royhall]

Thanks guys that's two contacts to keep.

Sent from my Nexus 6 using Tapatalk

[MCTID]

A long shot folks.........and I'm sorry that it's not about my venerable old Honda.

I have two Triumph 1970 650 Twin Crankshafts which I need to refurbish. Each has a cast Flywheel which is heated and shrunk on to the Crankshaft and held in place with 3 bolts. I think each Flywheel is cracked which makes them junk..........unless I can obtain the unobtanium - and find new Flywheels (hahahaha) - or I can find a Foundry who can cast some new Flywheels (using the old Flywheels as patterns) and a machine Shop who can make them fit.

Do any of you fine upstanding people know of a Company who might be able to assist me? I live in Lytham St Annes but TBH distance is no object (as long as its in the UK).

[Trigger]

Always check the rods because once they start knocking, it can oval the con rods.

[Trigger]

There is a company in Kent, Dial Patterns that could make the pattern for a foundry to fill. Don't mention my name as I still owe them funds

[MrDavo]

Thanks for the contacts, I'm not counting any chickens until I get her apart, but Trigger's firm in Bedford could be the way to go, I've had a look at their website, and I'm off to the Silverstone Classic in 2 weeks, so I could maybe drop the crank off on the way.

I still don't see why a big end would be intermittent, surely they clank all the time when they are shot? Maybe that thick 20/50 oil works better than I give it credit for.

I still have to find out why, and what the mystery sudden pressure loss is all about, or I'll be doing it all over again next year. Tomorrow the car will be banished outside so I can use the garage space and I'll start dismantling. The oil feed line feels a little squashed around the kickstart boss and footrest, I'm going to drain the oil by disconnecting the line at the oil pump end, and see what happens when I drain the tank while the oil is cold.

Edit:

Tell me more about the oil pressure relief valve, I see it mentioned in the similar thread by Yozzer74 - I now realise the one I checked and cleaned was in fact the leak stopper valve, also I checked the the sprung valve in the oil filter. Looking at this page:

http://cb750k2.honda4.nl/lubrication-system/lubrication-system.html

It seems there is another third valve which I haven't checked, and sticking can result in poor oil pressure. Worth checking first, or too late now?

[K2-K6]

You've a very unusual set of circumstances that look to be a possible cause.

If you think about "traditional" low oil pressure, that would be the engine bearings worn enough to allow the oil feed to leak out faster than the pump can put it in to fill the gaps.

What you appear to have is "within reason" a relatively unworn bearing set (unless further running totals it)but a restricted supply so the leak out is normal but refilling the bearings is not happening fast enough. The con rod upper shell is effectively prevented from getting much oil into the area during the power stroke and relies on the non compressive part of the stroke to replenish the oil that separates the shell from the crank. If you restrict the supply, that replenishment won't complete in the time available so the next power stroke gives you a clonking as the shell hits the crank pin.

The mains have nothing like the percussive load inflicted on them so as previously posted they'll generally not give the same sort of noise.

There is no real restriction going to the pump in a dry sump system but a collapsing feed hose would definitely make one that the pump could not overcome.

That's very informative from Bryan (hat off to him for remembering that) as it could be key to your problem. There's not many forum with that in depth level of knowledge available.

[Bryanj]

I remember it because my one time boss, Neal Frazer, who owns Frazers of Gloucester bought a K? from Skellerns of Worcester with all the goodies (Tank. bars, sidepanels,etc) removed and had the frame and swingarm nickel plated then built a "New" Dunstal. Two weeks later it started knocking and he had to take just the engine to Skellerns who took over a month to fit new crank, rods and shells also supplying the new oil hose. It may even be in the bulletin list--not sure

[MrDavo]

I have the hoses off, although I cannot be certain we've found the problem until I fit new hoses and refill with 10/40, the supply hose has a kink (not terrible but still a kink) where it bends 90 degrees, a simple but messy experiment pouring oil into the tank and watching it come out of the motor end saw oil coming out faster when the hose was straightened.



New OEM hoses are NLA (thanks again Honda), but an eBay search found a man in Germany who does a service exchange service fitting new stainless braided hoses to used fittings, not cheap and priced in Dollars, but the best I'll get.

Even if it doesn't solve my problem and I have to pull the motor I reckon that's what caused it, it will look better and I will have eliminated the poor feed. Interestingly my Haynes manual (I have little faith in these but at least I can take it in the garage unlike my virtual Honda manual) mentions bad oil hoses sometimes causing low pressure, so they must have read the bulletin too. A Google search tells me Honda bulletin 750#35 dated 11/72 was called 'Revised Oil Tank Feed Hose', but no trace of it online anymore, Ash will know, but it seems that the US site bottled it and pulled their online service bulletins - why the hell would Honda sue their loyal customers over copyright on 40 year old bulletins?

While I'm at it, Ive pulled the oil pump again, all looks well and I checked the pressure release valve too. A couple (literally) of metallic flecks on the strainer, also tiny bits of my new clutch friction plates but nothing scary.

[Green1]

That kink looks pretty severe to me.
If that was a rad hose you would bin it.

[MrDavo]

Well the good news is that the oil hoses arrived from Germany, and very nice they look too:



They were a struggle to fit, as they are not a millimeter longer than they have to be, and very stiff - it took a few attempts with each hose until I found the correct sequence of assembly so they would fit. I thought of spraying the stainless braiding black, but decided against it as they'd just look scruffy when the paint starred to flake off.

Anyway, that's the least of my worries, after I fitted a new filter and some new 10/40, I went for a test ride. From this picture, taken later in the day, you can guess how that went:



Fine until it got hot, then the knock was back. I limped home slowly, and dropped the oil. This time, because it was new and clean, I could see the dreaded 'glitter' in it, no question. Although I've fixed the cause, the crank is already goosed, and isn't going to fix itself. B*gger!

I've wondered about a second hand crank, DK have one, and I know a guy in Stockport with a load of used CB750 stuff. However what you don't know is why the bikes they came from were stripped / scrapped in the first place. Unless I go with a micrometer, measure every journal and compare it to the spec sheets, I could easily buy a whole load of more trouble. What do you think?

The motor is nearly ready to come out, I'm stupid busy this week though, so it may not get pulled and stripped straight away.   I am keen to see how bad it is though.

The contact in Kegworth seems promising, if only because its a lot nearer than Bedford, however there's always the post. How feasible is it to post a CB750 crank though? What would I have to pack it in? Probably not a Jiffy bag.

[K2-K6]

Hoses look good but a shame it's too far gone to get it going, I was hoping for you that you may have got something more positive out of it.

To send the crank, could you wrap it in clingfilm then stand it on end in a strong box on a polystyrene block and use expanding builders foam to in effect create a bespoke cradle to protect it?

[royhall]

I would wait until you strip the engine, before thinking about your course of action, your crank may be okay.

[Bryanj]

Cranks rarely go so a used one should be OK but get one with rods as if its knocking the rod concerned will be toast guaranteed

[MrDavo]

If that's the case then a second hand crank will be the answer - if I have to change a rod then I have to find one with the same weight (there are 3 grades) to match the others or the balance will be out. As Roy says I won't know for sure until I get in there, but there's not much doubt in my mind that a big end is fubar, after combining the knock with the sight of metalflake oil.

Sadly time and the need to reorganise in the garage to do the job means it may be a while, but I'll update you when I know more. I wanted to take the motor out to polish the cam cover anyway. 

[AshimotoK0]

I might have a crank to sell. I do have a collection of rods too but they are a mixed bunch from other cranks. I had both of my cranks miked last year by a top engineering guy who sadly passed away last year and they were both fine. Just need to check that they both are the types that take  M8 down to M6 advance bolts as Trigger told me  me that not all 750 cranks are the same up to the Auto ( I was previously told by a top sandcast restorer that they were interchangeable up to the auto), which has a HyVo chain. I want 25 quid for it if you are interested as long as both have M8 advance bolt tappings. Pretty sure the spare crank came from an F1 and I do still have the engine number somewhere.

I am in East Yorks BTW