2.1 The Combat Crankshaft.

Date: Wed, 7 Aug 1996 17:29:30 -0700 (PDT)
From: Ralph Merwin

S. Moseley writes:
> On Wed, 7 Aug 1996, b.a. schalke wrote:
> > I recently had my '72 Combat motor apart when I replaced the original crank
> > bearings with "Superblends" - good thing I did, because the timing side
> > bearing was just starting to go. Strangely enough, the drive side bearing,
> > which should see more load, looked perfect.
>
> Ditto, except when I got mine apart the timing side was well on its way
> out, the inner race being really gouged. I started hearing the awful noise
> at the U.S. border on a trip back from Vancouver, but rode it home to
> Bremerton anyhow. The drive side was perfect.

Almost ditto on my race bike (750 Commando). The drive side is fine. The timing side feels rough. Both are FAG Superblends. The local Brit-bike shop, DJ's Cycle Shoppe, says that the "hot setup" is to use a Superblend on the drive side to handle the stress, and a high quality ball bearing on the timing side. He says that roller bearings don't like spinning fast and tend to skip if not under load, as on the timing side. The ball bearing will handle the fast spin, light-load application great (I know that even the timing side has quite a load - we're talking relative terms here). So, that's what the 750's getting...

Ralph

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2.2 Alpha Bearings and Bigend Bearing Replacement.

Date: Wed, 16 Oct 1996 21:45:10 -0400
From: Gregg Kricorissian.

Hi Doug,

Sorry about the delay in replying to your query about Alpha big end assemblies: I'm still extremely busy at my "real" job. Though I also haven't been able to follow Brit Iron lately, I'm copying this note to the list, since it may be of interest to other list members.

At 02:19 PM 10/12/96 -0700, you wrote:
>.... regarding Alpha for the B50. I was curious as to others' experiences with
>them durability-wise. From the posts/responses I have received so far, I
>probably would not use one. There has been much said about them
>machining too much material, removing the hardening, poor/no radiuses,
>short lives, etc.

I've heard a lot of good and bad about Alpha bearings, and have personally seen bad ones. However, before we say too much about it, we should recognize that making a "good" big end is a demanding undertaking. It's very easy for a job-shop manufacturer (like Alpha must be these days) to "lose the recipe" because of the precision work required in procuring, machining, heat treating and finish grinding high grade steels. It can't be too easy to maintain control over all those individual hand operations in fabricating the assembly ... especially if you're making a wide variety of them, but only a few at a time.

In the good old days, Alpha had the economy of scale to keep the recipe in check. Now a days, quality may be more variable. Given the choice, I prefer to polish and refurbish and calibrate a used-but-excellent big end rather than take a crap shoot on an aftermarket one. However, on older machines, you don't often have much choice.

Also, I'll bet many of the horror stories we've heard stem from the mechanic's poor workmanship .... replacing a big end "properly" is a lot more involved that the simple process oft described in how-to books. An earlier posting from Ken Bell implied that Vincents were the only ones that required special fitting; not so, they all do. Something to keep in mind is that most roller big ends were built at the factory by "selective assembly" process ... the outer track was fitted to the rod, honed round, and roller (graded by 1/10 thou steps) were selected to give a fitted big end clearance of 9/10 to 1 thou. Not something to be taken lightly! Read on ...

My latest escapade with an Alpha bearing was the one from my friend Neville's pre war Tiger 80. He'd sent the rod to the UK (Serco, as I recall) to be re-furbished, and then brought it to me for checking and assembly into his flywheels. Big end ovality is the most common problem you'll find, chiefly because so many owners slog the engines around long after the original bearing has developed too much clearance. This Tiger was no exception! Unfortunately, the person who did the work in the UK did not bother to check the rod, literally slapped the big end race into place and assembled the rollers. This ovality must be corrected before any other work is done.

With the Tiger, my first hint of problem was a bit of drag in the bearing as I rotated the rod, alternating with loose spots. I decided to check the eye of the rod, but when I went to press out the big end race, I found that it was not much more than a finger-press in the rod!! Bottom line: the rod was oval, and the Alpha big end race was a bit undersize. Nothing much could be done for it, except return the rod and bearing assembly to Alpha .... who made good and then returned the assembly to Nev.

Here's the big end replacement process I recommend:
 

  1. 1. Find as many good rods as you can.
    1. - Remove the big end races.
    2. - Measure their big end eye diameters.
    3. - if you have only one rod, keep yours fingers crossed
  3. 2. Choose the best rod, the one that:
    1. - has the smallest eye ID, consistent with being round,
    2. - and the shank being dead straight.
  5. 3. Measure the bearing components ...
    1. - pin OD, roller diameter to 1/10 thou, the outer race OD and ID.
  7. 4. Determine how much the outer race ID has to shrink when fitted to the rod
    1. - aim for, say 0.001" fitted clearance on the rollers and pin dia.
  9. 5. If the ID of the unfitted rod race is 0.003" oversize, it will have to shrink by 0.002".
  11. 6. "Shrink" requires properly setting up the interference fit of the race in the eye of the rod.
  13. 7. This is the most important step:
    1. - determine the dimension of maximum ovality in the rod's eye.
    2. - that will be the *minimum* dia the rod eye *must* be honed to make it round again
    3. - With luck, this dia will be smaller than the OD of the new outer race
  15. 8. Determine how much the rod's eye will have to be honed out to give the right ID clearance
    1. - If you need 0.002" shrink, the race will need to be 0.004" interference in the eye
  17. 9. It's best to leave a little more shrink than you need on the race OD, then...
    1. - fit the race to the rod
    2. - ensure the race ID is *dead* round after it's fitted
    3. - hone the race ID to final size to give 0.001" clearance
  19. 10. Polish the race ID to a mirror finish
There you have it, a not a job for the faint of heart, and a darn sight more complex than using the new race to press out the old one in a vice! This brings about the final words on tools: When I refer to "pressing", I mean use a good hydraulic or arbor press. When I say "hone", I mean use a good Sunnen precison pin hone. Find yourself a good automotive machine shop that has the equipment, and the people who still know how to use them!

Having fitted the big end to the rod, then you can turn your attention to fitting that assembly to the flywheels, and truing to within 0.001 on the mainshafts ... but as they say "it's another story".

Hope this helps,
...Gregg

Date: Thu, 17 Oct 1996 20:55:42 -0400
From: Gregg Kricorissian

In my earlier note on roller bearing big ends, I detailed some of the pitfalls to watch for with rod eye ovality when rebuilding an engine. For the sake of completeness, I thought I should also draw attention the second most common problem you'll run into with thhe roller big end bearing: the condition of the crankpin.

You'll have to split the crank and pull the big end apart to check it, but many an engine will pass the time-honored "up-and-down" test on the rod while assembled, but will need renovation because of a marginal crankpin. Two problems frequently occur in the pin of a roller big end:

  1. 1. Pitting of the bearing surface due to corrosion
  3. 2. Spauling of the bearing surface, for any of several reasons.
Either of the two conditions usually spells sufficient cause for replacement, though light pitting may be polished out and may be passable in a lightly used engine. However, a spauling surface is a disaster waiting to get worse, and in *no* account should it ever be used in an engine.

Replacement with a NOS pin is the best course, if you can get the parts. Phil Irving, in "Tuning for Speed" describes another option which involves grinding the pin down, to take a hardened steel sleeve that replaces the original track, and brings the pin OD back to standard. The mod is completed by grinding the shoulders of the fitted sleeve square ... in many ways this can be an improvement to the crank's rigidity.

Of course, precision work of this sort comes at a cost, and can be entrusted to what seems to be a decreasing number of craftsmen. Fabrication of a suitably-hardened sleeve is not to be taken lightly.

Now for the Royal Enfield angle: some of you might know the Enfield's went to a plain bearing "floating bush" big end in its singles during WWII. At the cost of needing greater oil flow, and an efficient oil filter, the floating bush gave longer life and freedom from pitting and spauling of the pin. This development was based on testing done during the mid 30's, and became a feature of the Enfield singles right to the end of production.

Perhaps because the floating bush was made for Enfield's by Glacier, Alpha never made replacement big ends in this style, but rather supplied a roller bearing assembly through the aftermarket.

Hope this helps,
...Gregg

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