E: Engine Big End Replacement

Bill Thomas

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Are you going to pin the shaft ?, Well worth doing I think,
Not the mills pin , That is just a soft pin, Some of us drill the end and fit a small short roller ,
Half in the shaft and half in the flywheel,
And bash the end over to stop the roller coming out !.
Cheers Bill.
 

Cyborg

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Check your big end bores in the wheels first, and the pin diameter to make sure you will have enough interference fit before installing the mainshafts........
That certainly will bring the project to a quick halt. I think I’m ok in that department, but time will tell. The crank suffered a broken crankpin and the pin appears to be the original crowded roller variety. It took quite a bit of force to press it out the remains... that was encouraging. The new pin is +.003, so should be ok, but still have to do final measurements. If the math doesn’t work out, Robert will gleefully come to my rescue with a 1.250 pin, but that’s additional time and complexity that I would like to avoid. The new timing side mainshaft is +.005, so think I’m ok there. Just have to double check measurements and press it in straight.
 

Cyborg

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VOC Member
Are you going to pin the shaft ?, Well worth doing I think,
Not the mills pin , That is just a soft pin, Some of us drill the end and fit a small short roller ,
Half in the shaft and half in the flywheel,
And bash the end over to stop the roller coming out !.
Cheers Bill.
The drive side has already been pinned with a roller, so ok there. The shaft itself appears ok and bearings will still be a snug fit on the shaft. I chucked the drive side shaft in the lathe to make sure the shaft and flywheel were still straight after the explosion. Everything seems fine, but the timing side didn’t survive unscathed. I held the timing side in the lathe and it wobbled around. Normally I would have put it between centres, but one of the centres was completely knackered.... could have fixed it, but was easier just to press out the shaft, which was obviously bent. I installed the timing side flywheel on a 1” stub arbor and it appears to be straight. When the new shaft is installed, I can then put it between centres and confirm it’s ok. At this point, I don’t think I’ll bother installing a roller in the timing side shaft.... hopefully nothing arises that will change my opinion on that and I can achieve enough of an interference fit with the +.005 shaft. If it doesn’t go well, I’ll have a nice new +.003 bigend bearing assembly for sale.
 

Bill Thomas

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The holes on my 560 don't look good , So I shall pin both, If I can get my Backside in the garage !,
Really must have a go.
 

oexing

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I wonder how you can pin drill the mainshaft in the crank web, both would have to be "soft" . That is no good combination for a good press fit as you can wait for a seizure while having it on the press. And then, how do you ever disassemble that crank, you´d have to get the roller out - how so ? By spark eroder ?? The shear cross section of that roller is not so impressive anyway so my choice would be a parallel key with decent size to go with a nice press fit.

Vic
 

Bill Thomas

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I have said before, I hand sawed a mainshaft in half a few years ago,
And didn't know they were THAT soft !,
It's an old Race mod', Well known,
As for pressing out, The roller just slips out as you press, No problem.
It's drilled from the flange end.
 

Nigel Spaxman

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A friend of mine used to build two stroke racing engines for go kart racing. He had a high reputation for building winning engines. These 100cc Yamaha engines revved to over 15,000 RPM. He knew how to get all the clearances right. , what beaings to use, and how to adjust the ports to get the best timing for racing. People would pay a lot of money for one of his engines. He showed me how he trued cranks. The amazing thing is he did it by eye. If you use a piece of white paper against a black background as a straight edge and then rotate the crank on bearings when you look down over the crankshaft, you can see movement that measures as little as .0001" He had dial indicators as well but he prefered to use his eye.
 

Cyborg

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In post 183 above, David mentions “At the Vincent Factory, the flywheels were not paired just pick up from the bin and assembled”.
This is of interest because I have an extra orphan drive side flywheel with mainshaft. It looks perfect except for some minor surface corrosion. Nothing that would cause any concerns. It is quite possibly new old stock, but haven’t looked at it under magnification.

Anyone have any thoughts on using Vincent flywheels that didn’t leave the factory together?

Also any thoughts on using Loctite 232 instead of lanolin. 232 takes quit a bit of heat to break it free, so that might be a show stopper if one was to worry about future disassembly? Prevents galling and adds something to the stiction.

 

Chris Launders

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Someone may know more than me but I cant see any manufacturer machining flywheels in matched pairs, the cost and time would be far too much, maybe for factory race engines but I severely doubt it for normal use. Thinking about photo's I have seen of various factories there were just columns of flywheels stacked together.
 

Bill Thomas

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VOC Member
My late Brother in law, Who used to do machine work on Triumph 3 s,
Told me of a chap who stroked a pair of wheels, One at a time,
And it was a Disaster !!.
Maybe just get the 2 you want and do some tests ?, Maybe lucky ?.
Cheers Bill.
 
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