• Welcome to the website of the Vincent H.R.D. Owners Club.

    Should you have any questions relating to the Vincent H.R.D. Owners Club, or Vincent H.R.D. motorcycles in general, please contact Graham Smith, Hon. Editor and Webmaster by calling 07977 001 025 or please CLICK HERE.

    You are unrecognised, and therefore, only have VERY restricted access to the many features of this website.

    If you have previously registered to use this forum, you should log in now. CLICK HERE.

    If you have never registered to use this website before, please CLICK HERE.

E: Engine Big End Replacement

Cyborg

Well Known and Active Website User
VOC Member
Now that the B twin is more or less in one lump after more than 40 years in boxes..... I need to start organizing things for the next project. So... I have most of a Comet engine, but it needs a new big end bearing. There aren't many shops around this area that I would feel comfortable handing over a crank to. I'm thinking of taking a stab at doing it myself. Haven't started yet, so need to clean things up and start measuring to determine if I actually have something to work with. I have a press that should be sufficient for reassembly, dial gauges etc. Also have a lathe, but I'm thinking knife edge rollers would be better for checking runout.
Has anyone on here been through this process before? Advice?
 

Cyborg

Well Known and Active Website User
VOC Member
It’s an Inter crank and looks like steel. I recently broke down and bought a TIG and it seems like it it would be relatively easy to run a very thin bead around in there. There are a couple of holes in the flywheels that look like they could be used to pin the two wheels together, but will have to confirm that. With the timing side in the quill and the drive side in a chuck bolted to the mill bed, I can align the two half’s. Then a boring head would get it close to size and I could finish it with another sliding mandre come lapping tool, or actually break down and buy a proper lap. For a hole that size, they aren’t that expensive (just under $150 usd), plus it’s a size that I would likely use again.
 
Last edited:

david bowen

Well Known and Active Website User
Non-VOC Member
At the Vincent Factory, the flywheels were not paired just pick up from the bin and assembled, Con rods and big end pins were colour coded and there was a chart on the wall showing the coding and correct size needle rollers to use, same bench set of centres,and on the floor a block of lead ! which we use to tap the flywheels onto to get the correct read, ( Bob Culver still has that block or lead for the same purpose. ) the lead block about once a month the lead block was cut up put into a cast iron saucepan and cooked to get to shape back. that was 69 years back so whats changed,
 

Cyborg

Well Known and Active Website User
VOC Member
Another good trick is to drill and fit a small roller, Half in the flywheel and half in the main shaft, So the shaft can't turn. Cheers Bill.

Too bad this crank didn't have the roller you mention. If a roller had been installed, the fellow could have use a socket to tighten the new crankpin nut instead of a Milwaukee Speed Wrench!

Crank Speed wrench.jpg
 

Cyborg

Well Known and Active Website User
VOC Member
Sidetracked again Bill....Actually it had a key which became two keys. Strange.... the M/S was a snug fit and the nut was so tight, I couldn't break it lose with a 2 ft breaker. Had to use a 1/2" impact gun. Guess it tightened itself a 1/4 turn when the key broke.

Inter mainshaft key.jpg
 

Cyborg

Well Known and Active Website User
VOC Member
Thought I would dredge up this thread because I’m going to try my luck with a twin crank.
Question #1 is why use Lanolin when pressing in shafts and pins? Yes to prevent galling, but what makes lanolin better than some random petroleum product like vaseline?
Job 1 is to press in a new timing side mainshaft, so hopefully it goes in straight.
 

Bill Thomas

Well Known and Active Website User
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.
 

Cyborg

Well Known and Active Website User
VOC Member
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

Well Known and Active Website User
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.
 

oexing

Well Known and Active Website User
VOC Member
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

Well Known and Active Website User
VOC Member
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

Well Known and Active Website User
VOC Member
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

Well Known and Active Website User
VOC Member
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

Well Known and Active Website User
VOC Member
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

Well Known and Active Website User
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.
 

Latest Forum Threads

List of Forum Categories

Can't Find What You Need?

Buyer Beware: Fake or Real?

Top