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E: Engine Main bearings


Bill Thomas

Well Known and Active Website User
VOC Member
Does Martyn tell you to grind the centre out of the old bearing a nats, So it will slide on and off easy.
Good Luck. Bill.
When you get your new puller, Try and grind the middle edge of the tool to as thin as you can,
To get behind the bearing.
 

MartynG

Well Known and Active Website User
VOC Member
Bill,

here is just part of the article I wrote in OVR #18
"
Using whatever means at your disposal, dismantle the old bearings then open up the internal diameter of the inner race so that they are an easy slide fit on the main shafts and Vola! You have a set of spacers. You may need some professional assistance to open up the ID but once you have done so – you have a spacer set for life.
"

Martyn
 

davidd

Well Known and Active Website User
VOC Member
The Comet flywheels are easy to fit, but with the twins I have seen the pins and the nuts are all too wide to fit in a Vincent. I believe that is what Steveo is worrying about in the near future. What do the twin builders do when the big end pin hits the bearing race?
Vin_crank_bearing_installation_006.jpg
This is a Maughan flywheel a friend received. All the Comets are close to flush and the Comet and twin flywheels Terry builds are near flush as they have no nut.

David
 

greg brillus

Well Known and Active Website User
VOC Member
Bearings are dead easy to remove if you use a heat gun like I suggested earlier in this post..........Just heat the bearing up some and it will slide off with a pair of screw driver blades diagonally behind. The end of the pin sticking out from the nuts, just grind it away, sometimes even need to grind some of the nut as well, you only need a small gap to clear everything. Sometimes the ET 77 spacer can be different widths, so this does not help at times........Unfortunately when cases have been reclaimed in some area's there is little room for everything.
 

stu spalding

Well Known and Active Website User
VOC Member
As regards removal of bearings from shafts, with a pressed steel cage it is possible to get a small screwdriver behind the rollers and pop them out of the cage. It is then relatively easy to get a puller on the inner track. Afterwards the rollers are replaced and the cage dressed back to its original shape. Tony Maughan taught me this one so it must be OK. Cheers, Stu.
 

Chris Launders

Well Known and Active Website User
VOC Member
I don't know if this would apply but when building my JAP engine on which I had machined the casings myself from castings I made some accurate replica bearings from engineering plastic with fractionally more inner and outer clearances so they were a light push on the shafts and in the housings so the crank could be fitted and clearances measured and adjusted without any force or doing damage to anything.
 

Bill Thomas

Well Known and Active Website User
VOC Member
As Greg says, after all these years anything could have been done,
There was a bit some years ago, Where the Crankcase faces were ground/reclaimed, And nothing fitted because the Cases were now too narrow.
I had a problem with my L/ning, After the gearbox was welded at the top, The top face was all over the place,
But I just use silicone, Which won't do any harm, It's only the gearbox.
They were scrap from Africa, So I had nothing to lose.
 

SteveO

Well Known and Active Website User
VOC Member
Bill, does the bearing have to go on a certain way round then? There is a thin side and a wider side? I hadn't noticed this, I put them on with the engraving facing out, is this wrong?
 

Bill Thomas

Well Known and Active Website User
VOC Member
In does not matter, But as per Greg's photo, The steel cage is bigger one side and might get damaged
Trying to pull it off, The old brass cage type was the same both sides.
Try Greg's way of heating the bearing with a hot air gun or hair dryer ?, Sounds good to me, but I have not tried it.
 

greg brillus

Well Known and Active Website User
VOC Member
Learn't to use a heat gun all the time when I worked in aviation, as many bolts and pins are a very neat fit into holes in alloy brackets or similar and you can't use a naked flame. The heat guns will get things very hot if you apply it for a length of time, but the bearings come off without too much trouble, even though the shaft absorbs some of this heat. There are many ways of doing things, but some are just easier and much faster.
 

Tony Wilkinson

Active Website User
VOC Member
Bill, yes I thought the oil scroll was going to fix the problem. As I said above, my engine actually lacked this part. But it's made no difference. I appreciate that I need to centralise the rods, but there seemed little point in moving on to this before I got the crank turning without banging into something! I have had a mail conversation with Davidd on here and he suggests a cheap bearing seperator, ground to fit, to start the bearing off the shaft, so that is my next purchase. My thinking now is that since I probably need to shim the bearing to get clearance anyway, I am going to have to go with whatever that takes and hope the rods line up. I have to get the drive side free turning, as that is the side that is tightened up against pulling the crank over, not the timing side. I don't like the fitting on the main much myself, it is horrible, but I'm stuck with it unless I either scrap the case for a modern replacement or undertake major machining work that I can't do myself. I do have some F1 contacts and an engineer friend who told me that TZ750 Yamahas were raced in the Island with the bearings glued in with Loctite. I dont intend to use the bike THAT hard! In the meantime here are some photos of the crank. I am starting to wonder where this build is going as every time I fix one problem another crops up; it's beginning to get me down if the truth be told...
It is true that main bearings in TZ Yamahas were (are) often put in using Loctite to stop them spinning in the cases. I used to do it with mine as well. The difference being, TZ's are revved to well over 10000 RPM.
 

oexing

Well Known and Active Website User
VOC Member
Actually the bigger difference is the horizontally split engine case - no ? In that case you cannot easily have a good shrink fit when assembling the engine so in consequence you see walking races after some higher mileages. Unless there are features preventing races to spin like keys or pins so no spinning is possible.
Good engineering really cares for light shrink fit gripping races well enough till a bit higher than operating temperatures. I go for sizes that free races at about 120 degrees C so no big problems with spinning races and no factor in internal play in the bearings when hot.

Vic
 

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