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ET: Engine (Twin) Installing ET92 Inner Roller Set on Mainshaft

craig

Well Known and Active Forum Website User
VOC Member
What is the best method of installing these inner roller bearing sets ET92 on the mainshaft?
I appears to be a 0.0015 interference fit.
MO32bearingset.jpg
 

Robert Watson

Well Known and Active Forum Website User
VOC Member
That sounds a bit tight

warm them in the oven, slide a tube on top of them that contacts the inner race, beat it like a circus strongman bell! Where is my tongue-in-cheek emoji

Oh - make sure you have C3 fit bearings or lap the ID of the outer race so the correct clearance is there
 

greg brillus

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VOC Member
I just hang them off a rod in the vice and heat up with an electric heat gun........Then they just slide on no problem........of course before you do this, you should make sure the crank/rods are centered as best you can and this often takes a shim between the bearing and the flange on the outer flywheel face.........use an old center of a E 91 bearing and dremel the center out until it slides freely over the main shaft.........Just cover the bearing with a rag and smash off the outer race, cage and ball bearings. Often too the shim will not sit flat against the flange due to the center hole of the shim being to exact a fit, so again with the dremel, chamfer a radius on the inner of the shim until everything sits nice and flat against the flange.........Good luck with it all.........Cheers.........Finally something worth discussing on this forum again without everyone getting upset.
 

oexing

Well Known and Active Forum Website User
VOC Member
Actually 1.5 thou press fit of inner race on mainshaft is a LOT ! No wonder people had to "lap" components of bearings for more play. But this press fit is not so easy to measure up so are you sure it is that much ? I want 0.005 - 0.01 mm light press fit for inner races anywhere - or less than half thou in your money.
In recent years I have gone to have plastic dummy bearings for checking all fits in engines. The POM dummies got min. 2 thou play in all diameters but exact same width as real bearings. So with these you can test assemble gearbox or crank components without having a need to take out bearings again because you got some shims not quite right - often frustrating to do with all new bearings in place.

Vic
 

Chris Launders

Well Known and Active Forum Website User
VOC Member
Vic
I made plastic bearings with a light fit when building my JAP engines from scratch to enable me to set everything up without having to knock bearings/shafts in and out several times.
 

greg brillus

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VOC Member
The bearing tolerances can be all over the place too, the ID and OD's can vary by a thou or so depending on the manufacturer. The bearing that gives the most trouble I've found is the small timing side roller ET 94 the thin outer ring collapses once the case cools and then the inner race is too tight a fit........this is very common and often left that way which is not good........ I take the case half in to my engine reco shop where we hone the bore to give the correct running clearance.........This is also a common problem for people installing a new big end assembly to their crank.........often the clearances are too tight. A descent hone is the only way to correct these issues........well if you want the engine to survive with some piece of mind.
 

Bill Thomas

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VOC Member
I have never seen this before , But a set of Comet cases, I have just bought,
Had a flywheel assy in it , And one of the Big inner bearings was so tight,
It would rather come off the shaft than out of it's outer !,
He's hammered all round the outside of the outer, Don't know why,
Will be interesting trying to sort it ?.
Also the big end has no side play and does not want to turn much !,
Can't think it ever ran like this ?.
Cheers Bill.
 

Bill Thomas

Well Known and Active Forum Website User
VOC Member
As a matter of interest, How thick is the case hardening on a big end or Main bearing ?,
How much can you take out before messing up ?.
Cheers Bill.
 

oexing

Well Known and Active Forum Website User
VOC Member
Bearing steels are not case hardened, these are through hardening steels with high carbon and a bit of chrome. So you can take out a lot of material , like for different size of needles , and still correct hardness .
Tight big end bearings are a safe way to cathastrophe as nil clearance will not get better with a warm engine - all steel, same heat growth.
A different situation with bearings sitting in the alu cases: I do my calculations for shrink fits with target of outer races getting loose at around 100 degrees C so in normal use races stay put and no relevant reduction of running clearance at operating condition will be seen. I don´t mind having some minor drag in the bearing while the cases are cold. You don´t run a bike with cold cases for long time so I don´t see why one should mess up a new bearing by questionable "lapping" stunts - provided all sizes in engine cases and shaft diameters are within specs. A small amount of "preload" in the cold bearing sitting in the alu case is not a big deal , think of Velocettes or maybe HDs with taper roller bearings for crank main bearings: These require a certain preload of some thou in cold engine as the hot case will expand and when not setting preloads before you´d end with excessive play in a hot engine.
So check sizes in case and shafts for correct dimensions. Well, you should be prepared to find all sorts of defects in ancient engines with unknown history so no simple job here . . .

Vic
 

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