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ET: Engine (Twin) Primary side main bearings

Albervin

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I am now into the rebuild of the Shadow engine. I have heard there is a mod. for fitting two tapered roller bearings, back to back on the primary side. Has anyone done this? Details please.
 

greg brillus

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I've just done it to my race Comet engine, it is a great mod.......not the easiest thing to carry out as the distance spacers between the bearings are critical. It does rely much more on the clamping affect of the crankshaft nut being done up very tight to keep the bearings in place. I'm not sure for a stock road engine if it would be worth the extra effort over just replacing all the stock bearings with new ones.
 

Robert Watson

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How much crush did you give the bearings?

I have to say I have replaced the bearings whenever I have taken it apart because they are so cheap why wouldn't you? Nice for assembly as well. Crank in the timing side first and then just drop the drive side on and cinch it up, no fussing about trying to get the rollers to go in the outer race.

Mine was done by the previous owner, I think the bearings got changed about 60 or 70K miles a go, winter of '99- 2000.
 

greg brillus

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No crush on the bearings, they have a tiny amount of float, difficult to measure.......John Trease here in australia told me to shim it up then do the crank nut up very tight, then you should be able to wiggle the timing side shaft just the smallest amount, so just a small amount of play in the bearings. They do not need any crush , because they are back to back, there is no expansion between the two, not like a Velocette or a bevel Ducati crank that do expand. I did not modify the bearing races either, I used the center stock circlip which I de -burred first to remove any protruding edges, then I modified an old ET 19 alloy spacer to get the inner bearing located where I wanted to locate the crank as best I could, the outer bearing cup up against the outer side of the circlip. Then made up several spacers to go between the two center races, and fine tune to get the shimming correct........this takes many goes to get right. The tension of the crank nut is especially important, if it comes loose then the bearings separate and the crank would become quite noisy I would imagine. Like I said, it's a great mod but takes some setting up to get correct.........This is the same bearing set up that Neal and Rodney used on the new series"A" twins, I would say from advice given by John Trease who did all the machining on the new twin engines.......sadly no longer with us.
 

Robert Watson

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Mine is a new steel housing that held in place by a flange with several c/sunk screws going into the cases. it has a shoulder near the midpoint and the outer races go tight up against that. The cups then go face to face and are held apart by a hardened spacer. Put it together with a spacer that is close and tighten it all up. Then measure the end float. If you end up at 20 thou, the spacer is ground to reduce the float to .003 less than zero (in the sample stated .023 reduction) and voila. It been that way a loooooong time! It also has a seal housing which screws LH thread into the outer end to seal the whole plot.

Sorry no pictures, as I said I haven't seen it in close to 20 years.
 

MartynG

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VOC Member
This drawing was passed on to me a while back. Sorry about the quality as I do not have access to an original, only a photocopy received second hand. It author is Dr Doug from Australia. and here are some of his words.


========================
Vincent Main Bearings. Almost from their inception the Series B and C machines have had the drive side inner main bearing move in the crankcase and thence the bearing cup move in toward the crankpin.

Some riders seem insensitive to the “Clonk, Clonk” as the very hard bearing “Machines” a groove in the crankpin nut that delivers “Shrapnel” to the sump to be pumped through the entire lubrication system causing inevitable havoc. The original “OEM Mains” were supplied by Ransome and Marles and were of high precision and quality. The R&M bearings were selected from THREE possible “Fits” that were available at the time. The “Fit” was achieved by the internal clearance within the bearing. The bearings selected were of the type that allowed for a Tight fit in the crankcase and a tight fit on the mainshaft. The machines were produced many years before the advent of “Loctite”.

The method of fitment was to heat the crankcase to 200 Deg C preferably in an oven, the coefficient of expansion of the aluminium used (DTD 424) was 0.000022 per Deg C. The correct “Crush” on the bearing O.D is 0.002 Thou in TOTAL.. This was obviously not enough. When the housing was originally machined at the factory the level of precision required would be doubtful with the machinery available at the time on a “production line basis”. (ie) Bearing O.D. – 2.500 Dead, housing 2.498. The actual machining marks (turned” would have allowed “Bed Down” and in due course the bearing Rotates in the housing and results in an “under-sizes fit.

Further, ham fisted subsequent Re-fitting of mains WITHOUT a guide mandrel caused more damage as the bearing is entered into the crankcase. Many owners would not have the facilities to get the cases evenly heated and or hot enough without suitable pyrometers and adequate heating gear. Over the years the original mains have been not only in short supply but “extinct”. Some owners have fitted the wrong type of “Clearance Bearing” resulting in very rapid bearing wear. Many bearing supply houses are not even aware of what the “Right Bearing” is. The fact that the bearing I.D, O.D and width are the same has nothing to do with the INTERNAL clearance of the “Correct FIT”.

What Then is the Answer? Tapered Rollers are the answer.

I first heard of the fitment of same by Gordon Colquhoun of Moto Vincent fame. I wrote to him and he was most generous with his information. The “Moto Vincent” was a formidable machine ridden by Charlie Rouse.

Timkins take BOTH radial and axial Thrust and are fitted in pairs BACK to BACK and therefore CANNOT move inwards as the original ball and roller set up did. They can also handle more RPM than a Vincent could ever rev to. Some precision machining is required but it’s not rocket science.

Drive Side Rollers 006.jpg
 

vibrac

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VOC Member
I must admit I have not heard of this mod it sounds an excellent wheeze my only caveat is that I am supprised that this mod has not been offered by maughns or other engine gurus over the years I wonder why?
 

Bill Thomas

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Is it only me who likes the Lipped outer race for the inner main bearing ?.
Our "A" Man told us about many years ago,
They can't walk out !!.
Like all Mod's it needs some playing around, I helped fit them to Big Bill Telfer's a long time ago and
Have a set for my new Comet.
 

passenger0_0

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VOC Member
Interesting idea Bill to use lipped bearings.

My view is that main bearings walk out due to three causes.
1. Misaligned flywheels.
2. Misaligned main bearing bores.
3. Crank flex (too many revs using standard crank).
My view is that loose or walking main bearings are a symptom not the cause of a problem. A good indicator things are not good.

I can't help but wonder how much as been written on this subject?
 

Bill Thomas

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I agree David, But we have to do the best with what we have.
To me it's a Miracle our Bikes are still going well.
For me it was a mistake to change from the "A" type Mains.
I got fed up with Bodging mine with Loctite, Which didn't work !,
I was Sprinting and Road Racing for 10 years, So I was a bit hard on Poor Old Girl !.
So I took the cases to a Top Man, Another Mistake !!.
We took a Comet Engine apart some time ago, I don't think the Comet has as bad a problem as the twin's,
Because the Crank is more narrow.
But we could not get the outer main out !!, No matter how hot we got the cases.
Turned out the owner before, Ground some "Huge" flats on the outer track and bashed the alloy over them !.
 

BigEd

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VOC Member
VOC Forum Moderator
Is it only me who likes the Lipped outer race for the inner main bearing ?.
Our "A" Man told us about many years ago,
They can't walk out !!.
Like all Mod's it needs some playing around, I helped fit them to Big Bill Telfer's a long time ago and
Have a set for my new Comet.
I am pretty certain that when I had a new big-end in my Rapide the drive side mains were fitted with the lipped mod so that they can't move. I'm not planning on having a look any time soon. (Fingers firmly crossed.)
 

Bill Thomas

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VOC Member
I think you can only get the bearings "Full width " ?,
So have to get the outer ring ground more narrow for the Vin',
The grinding may make the track "Magnetic ", So that has to be reversed or it could cause problems ?.
I can't remember if both the bearings should be narrow or just the drive side where the alloy spacer and oil scroll goes ?.
 

roy the mechanic

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VOC Member
Timken main bearings are not a new idea. H-D have been fitting them since at least 1936. They are fit and forget. A well known vin racer(name witheld) has used them with 100% satisfaction. When asked he said"Ihave to use them as I run oversized mainshafts". I am yet to be convinced about the clearance as H-D manuals give 3-4 thou nip. Like in a car differential pinion bearings.
 

ray vinmad

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VOC Member
Even if your flywheels are running dead true, don't forget that any vibration you feel is transferred from the counterbalanced flywheels to the rest of the machine via the main bearings.
Ray
 

Bill Thomas

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VOC Member
So with the taper bearings, You can't use the scroll and alloy bit,
Does that mean we have to fit a seal ?
 

roy the mechanic

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I figure the scroll would be the start of the spacer, main seal makes sense, watch out, I bought the seal and motor sprocket from the same supplier, had to machine a bit from the inside of the sprocket to stop it binding on the fixing screw heads|
 

Robert Watson

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VOC Member
20180122_142403_HDR.jpg

These main bearing outer races don't move. That's on top of .002 interference.

Also I meant to mention in my recent post about tapered roller mains. They were in the engine when I assembled the rest of the machine. After startup it went 100 miles and had a catastrophic failure. The bearings were made by Bower and the steel cages which separate the rollers were defective, they were cut 95% through at one end. One got caught by the bearing and rolled the whole cage up into the rollers. We only know this because the other one had not failed and is to this day sitting on my bench to remind me to check parts you get from even the most reliable sources. It was then i did a lot of research on fitting them with .003 crush. I talked with bearing suppliers, manufacturers reps and a lot of experienced people. Answers ran the whole gamut from "no wonder your bearings disintegrated" to .003 is not enough. In the end I settled on .003. That was some 120,000 miles ago. I don't worry about it any more.
 

Cyborg

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VOC Member
I think you can only get the bearings "Full width " ?,
So have to get the outer ring ground more narrow for the Vin',
The grinding may make the track "Magnetic ", So that has to be reversed or it could cause problems ?.
I can't remember if both the bearings should be narrow or just the drive side where the alloy spacer and oil scroll goes ?.
You can still get the narrow bearings or you can use the wider ones with a narrow ET77 and ET19 or you can take the wider bearing race and just chuck it in the lathe. Leaves a nice finish.

Bearing narrowing.jpg
 

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