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Discussion Starter #21
mr.pete said:
Loctite won't prevent thermal expansion.It's useless in this case,and the bearing will still roll around in the crankcase when the engine heats up.
Even with 0.0025" interference,they still do some rolling around,even when Loctited.At 0.0025",it doesn't create much of a problem.

You probably need to get the outside of the bearing hard-chromed or nickel-plated,to make it bigger.Maximum recommended interference fit is 0.003".If it's tighter than that,the bearing may not turn freely,even with a C3 clearance bearing (which you should be using on the T/S).
Thanks for the reply.
I don't have an inside micrometer with which to measure the case bore but I have a friend that probably does. I'll try to get some good measurements before I proceed.
-- alonzo
I took my case and new bearing to Jerry's Triumph in Little Rock today. He held the bearing up to the case bore and said "no problem." When I explained how the bearing had been loose in the bore even after it had cooled quite a bit he just said that he had never had a problem with one and generally didn't even use LocTite. (had only used LocTite in the very worst of fit.)

So. Answers to my question have been all over the place and I'll now have to make some decision about how to proceed. My machinist friend measured the case bore and the bearing OD and came up with the bearing being only about .0005" to maybe .001" larger than the bore. i.e., not too snug!

Hard chroming the bearing is not very feasible for me but maybe other plating options are (e.g., zinc plating.) Does the plating material really matter here? Would .001" of zinc be as good as .001" of hard chrome?
Better than trying to shim it I think and electrolysis shouldn't be an issue here.

Thanks for any info.

-- alonzo
 

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Spin a main bearing in the case, and the fix will be rather expensive and possibly invove needing a new case half.

YOU MUST HAVE A SNUG FRICTION / LIGHT PRESS FIT when cool. If you follow the other shop's advice that it's okay to fit without loctite and it's already loose in the bore, make sure he's willing to pay his share of the repair cost when it goes.
 

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Discussion Starter #23
Spin a main bearing in the case, and the fix will be rather expensive and possibly invove needing a new case half.

YOU MUST HAVE A SNUG FRICTION / LIGHT PRESS FIT when cool. If you follow the other shop's advice that it's okay to fit without loctite and it's already loose in the bore, make sure he's willing to pay his share of the repair cost when it goes.
Thanks GPZ.

The bearing was not loose in the bore when everything reached room temp. What bothered me was that the bearing was loose when the case had cooled enough to be touchable (not where you could really keep your fingers on it) and the bearing had warmed up considerably.
I'm guessing that the bearing would be snug any time that it and the case were the same temperature. But, I'm also "guessing" that the case would warm up faster than the bearing therefore creating a condition where the bearing outer race "could possibably" spin.

The new bearing is the same OD as the old one and there is no evidence that the old bearing had ever spun in the case bore.

BTW: have you ever seen where a mainbearing had spun in the case on a unit Triumph? And, if so, did it really wallow out the case?

-- a
 

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Yes, the cases get badly damaged if the event happens at any significant speed, load and/or continued use.

If the bearings are not a light press fit when the cases are thoroughly heated, they will surely spin when the bike gets up to operating temps and certainly when run hard.

It gives me a good deal of concern when main bearings can be removed or installed by hand without heating the cases up in an oven.
 

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Hope you don't mind me butting in GPZ, but this is of interest to a lot of people on here I should think:- so are you saying that using Loctite (one of the 'Bearing Fit' grades) should be ok in the situation Alonzo's describing, ie: not enough interference but not yet actually spinning & causing damage? I ask because I thought this was precisely the sort of application Loctite Bearing Fit was intended for, and it's a bit disconcerting to think maybe it's useless.
 

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Loctite is useless in this application.It won't prevent thermal expansion,and the case becomes loose on the bearing.
Even when the bearings are a tight fit,Loctite does not prevent them rotating.They still roll around in the case when the engine is hot,but they should not be skidding.

There was some discussion on this at the Norton forum on Britbike,within the last year.

Chrome or nickel plating would be better than zinc.The bearing would need to be sealed with wax,or otherwise sealed,before plating the outside.
 

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Discussion Starter #27
Loctite is useless in this application.It won't prevent thermal expansion,and the case becomes loose on the bearing.
Even when the bearings are a tight fit,Loctite does not prevent them rotating.They still roll around in the case when the engine is hot,but they should not be skidding.

There was some discussion on this at the Norton forum on Britbike,within the last year.

Chrome or nickel plating would be better than zinc.The bearing would need to be sealed with wax,or otherwise sealed,before plating the outside.
The advantage, to me, of using zinc is that I can do it myself. I've made some tests and have some fair idea of plating thickness vs. time and feel that I can add .0010" to .0015" to the diameter of the bearing pretty easily.
I was planning to make a "sandwitch" to enclose and seal off the bearing's working parts (think Oreo cookie) but hadn't thought of using wax. I'll definitely give that some consideration.

I will test with the old bearing before I try the new one.
Please let me know if I'm about to do something really stupid.

-- a
 

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I'm keen to get to the bottom of this question because I have come across bearings that have been turning either on the shafts or in their housings several times over the years. Today I emailed Loctite's technical help team to ask for their opinion. I used this particular main bearing situation as my example, and stated that the proper interference fit should be between .0015" and .003", but in this instance the interference appeared to be only .0005". I specifically asked whether any Loctite compound would be effective in locating such a bearing, the application being a 750 Triumph with typical case hardened steel bearing outer race in sand cast aluminium crankcases, and with the full operating temperature of such a bearing/housing in mind. Here is the response I received:

"It is correct that the bearing needs a higher interference when press-fitted. However, this is without any Loctite, in which case the fit relies upon the 20-30% contact area that is typically achieved with press-fitted parts. The Loctite spreads the load over 100% of the bearing face, allowing it to carry more load. The coefficient of expansion of the product in the c70% of the contact area is higher than that of the aluminium, so full contact is maintained at running temperatures. Use Loctite 648 or Loctite 270, these are both designed for this type of application. It is important to apply the product over both surfaces when assembling a press-fit, to ensure that it has filled all the voids. Loctite 648 is a higher strength, so heat will be needed to remove the bearing at a later date. Best regards, Peter Martin-Flaven, Application Engineer, Loctite/Henken"
 

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Interesting about the 648 Loctite. I would be tempted to try it, if I could not plate the bearing.
It would surprise me if you would be able to get shim material around the bearing.
 

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I'm keen to get to the bottom of this question

"The Loctite spreads the load over 100% of the bearing face, allowing it to carry more load. The coefficient of expansion of the product in the c70% of the contact area is higher than that of the aluminium, so full contact is maintained at running temperatures.

Best regards, Peter Martin-Flaven, Application Engineer, Loctite/Henken"
At 90C./195F. (not the highest possible crankcase temperature),the bearing has expanded more than 0.002".The crankcase housing has expanded more than 0.004",and that's on approx 2.8" diameter.

Loctite must have an astronomical expansion rate,if a thin film 0.0001" or so thickness can manage to expand more than 0.001" on either side of the bearing.The crankcase expands less than 0.2%,but the Loctite expands 1000 %?

Loctite do make good products,but I think this is just too optimistic.

The real-life results just don't agree.The bearings will still roll in the housings with 0.0025" interference AND Loctite (admittedly,it might be 620 but that still has good temperature resistance).

It could be something to do with the piston pushing a force around 5000 lbs on the bearing and housing.Even with some interference,that's enough to stretch the housing so one side of the bearing isn't even touching.The lower side of the bearing will be pushed hard against the housing,but it can still roll.

Loctite is better suited to electric motors,where these harsh conditions don't exist.
 

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Discussion Starter #34
The Results

Well, the bearings are in. I zinc plated the TS bearing up to about .0025" interference and it went in with just a couple or three taps and snugged up in the case bore within a few seconds.

The DS bearing was zinc plated up to about a .003" interference and it went into the case with 4-5 taps.

In both insistence's the case was heated to ~100 Deg. C (spit sizzlin` hot) and the bearing frozen to ~-10 Deg. C.. No LocTite was used.

I did attempt to use bearing retainer (Permatex (64000) High Strength Sleeve Retainer) the first time I attempted to install the TS bearing but the bearing only went in about 1/3rd the way. I put the Permatex on both the bore and the bearing surface (per Permatex instructions.)
Also, I did spread the Permatex over the entire outer race contact surface (unlike Hughie Hancox who just dribbled it down the center of the bearing race. (in his video))

Second attempt at the TS bearing I only put the Permatex on the outer race of the bearing but it still would not go in more than about half way.

Third attempt at the TS bearing (and first attempt at the DS bearing) I used NO Retainer Compound and things went smoothly.

What I found here (and through some experimenting on hot aluminum scrap) is the the "anaerobic" sleeve/bearing retainer starts to "kick" as soon as it touches hot aluminum. I don't know how Hughie gets it to work. Maybe a different retainer compound than what I used???

Anyway, I'm pretty happy with the results.
How will the zinc plating hold up? Have I made things better or worse than before... I don't know. Pure zinc is softer than most aluminum alloys and I'm guessing that if the bearings do turn in the bores is that the zinc will go first (hey, we all want a little zinc in our oil!) I'm tempted to put a mark on the bearing races and on the cases so that if I ever have to do an autopsy on this engine I'll be able to see if the races did, in fact, spin in the case bores.

Thanks again to everyone who gave input on this.

-- alonzo

BTW: here's a photo of the bearing "sandwich" prior to plating:

I used 1/4" tempered hardboard (Masonite) with additional 2 coats of lacquer (to waterproof).
 
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