Crankshaft shims a10 preunit

[fido]

Yes, that hex head nut looks like a useful modification.  It will still be scary to remove and difficult to refit because of having to compress the spring before the threads meet but not as crude as the original 

[RichardL]

Fido, et al,

I don't recall, from the first time I put the engine together, that I had to pre-compress the spring to get the nut on. Hopefully, it won't be that long before I am reminded. I believe the geometry of the nut is, fundamentally, the same except there is no dished-out portion where the cotter pin fits in. SRM advises to make it so tight that it will never loosen. Regardless, I will also use some Loctite.

With regard to the nearly immeasurable end play, I ended up doing what I threatened, rather than buying a dial indicator. That is, I took 20 readings in each direction while using the digital caliper. I stabilized my measurement approach, always measuring to the same spot on the right-side journal face and keeping my hands as stable as possible while measuring to a precision-machined guide block laid across the oil-pump landing zone and the side opposite. Averaging the readings rendered a result of 0.0016" end play with a standard deviation around 0.0006". To me this was indication, enough, that I have it about right.

With regard to the tightness of the bearing to the crank, I have decided to leave it in place without adding Loctite. I had heated the bearing before fitting it to the crank in a cold garage. Though it wasn't extremely tight going on, it still had to be driven home. I don't expect the heating of the engine to result in the bearing becoming loose (due to expansion of the bearing race), as the crank will be at the same temperature, or nearly so, and crank and bearing race have the same coeeficient of expansion.

I suppose this is a lot of elementary mechanics to some of you and, as always, I appreciate more epert advice and opinions. Also, though it is a lot of chatter, it is more interesting, to me, than the next thing I must do. Work.

Richard

   

[RichardL]

Hey Guys,

Now that I've split the cases and see what's going on, I decided to change topics from "How bad is this!?! **UPDATE**" to this one here, since it closely fits what I want to show and, oddly enough, has a lot a discussion from my last shimming and bearing-fitting attempt.

Looking at the video linked below, you will see that the inner race is juuuust a tiny bit loose. This measures out to be right around 0.0012" oversized. I think it's too much to trust to Loctite, but would love to hear that I am so wrong, because that would make the fix so much easier.

As far as the cush nut goes, I was a bit surprised that it was not harder to remove (not dead loose, but not seeming like 65 ft/lb). The nut was still hard up against the sliding cush piece with the spring compressed, so I don't think the looseness was the result of hammering. As I mentioned in a previous post, the inner race did not go on easy

  http://www.youtube.com/watch?v=OqDcQTP9xmg&feature=youtu.be

[muskrat]

 G'day Richard.
I'm sure Loctite 641 will handle that bearing clearance. Get yourself a SRM nut and is tightened to the 65 ft/lb, all should be good. I use 263 on the thread.
A tip is to assemble all the s/a parts on the crank (bar the spring) to measure the end float. Then again when you have inserted the shims and used the Loctite on the shaft and bearing so the shims are clamped while the Loctite goes off (say overnight). Then you can throw it all together.
Cheers
ps good to drag out old posts if they are to do with a current problem.

[chaterlea25]

HI All,
Richard
I'm presuming that your shim stack is still going to be around the 0.037/8in  ??
Once a shim was lost from the stack then the pressure lessens on the cush drive nut
With that thickness of shims I would go and have one solid shim machined to fit
Years of experience at working in a power station taught me that one properly sized shim will out last a stack of thin ones by a huge factor

If there is wear on the crank splines the drive and deceleration thrust will force relative movement between the drive sleeve and crank, along with between crank spacer/bearing /shim/crank face, and at the the cush drive nut

Nearly all the A10 engines that I have worked on were worn on the splines and on the bearing seating

HTH
John

[coater87]

 I dont really know if this is a possibility or not, but we had something similar happening at work on some very large equipment a couple years back. These shafts spin at 5000+ RPMs and weigh nearly a ton. They were fine for years and years until the shaft bearings wore.

 After our millwrights replaced the bearings and shims, a few weeks later the shims disintegrated. The machines cannot be run like that, and its a major two day job to redo the shims.

 The poor guy who did the original job was thought to have done it incorrectly.

 After the job was redone a second time, and the shims lasted 4 days- much investigation was done.

 It was found the original shims were a very tight fit (inside diameter) to the shaft journals, and the replacements were a loose fit. Shims were custom made in house that needed to be driven onto the shaft with a custom mandrel- end of problem.

 The thought was the loose shims might not have been spinning at the same RPMs at a given moment they were needed to do there job. Maybe many times an hour and this could have been the reason they did not last.

 Its a theory- right or wrong. Either way, they seem to be lasting like the originals.

Lee

[RichardL]

Musky and John,

Yep,  I've had the SRM nut for some time,  cinched to 65 ft lb. So,  why 641 insted of 638, each of which appear to require 250 C.  for disassemmbly (the 638 filling biggger gaps) .  I've not used either,  so curiosty based on data-sheet info. The machined shim seems a good idea but I think I'd want about three,  to go +/- 0.001 either side of the calculared size.  Then,  theres's the whole issue of assembling with Loctite on the chance that you might miss the target once or twice.

As for fabricating the shims,  how?  I would be guessing grinding.

Richard L.

[bsa-bill]

The thought was the loose shims might not have been spinning at the same RPMs at a given moment

AHA something that's not been mentioned before, inertia, sounds maybe a bit far fetched but could the shims be loose enough to rotate on the crank during acceleration / DE-acceleration
 

[muskrat]

Not if they are clamped between the web and the bearing by the nut, Bill.
I just had to correct my last post. 263 on the thread.
The 641 has enough gap filling properties for your 1-1/2 thou and can be disassembled. The bearings with the plastic cage are easy to get off once the rollers are popped out. A solid shim would be easy to make with a surface grinder and magnetic chuck/vice.
Cheers

[chaterlea25]

HI Richard ans All,
Do you have access to somewhere that will do one off machining to make the shim ?
and or a local engine repair shop who will have a shim grinder
I would not loctite the bearing in place until you are sure the clearance is finalised so as it will be easier to undo for correction.
You should be able to arrive at the correct thickness if you have loose shims to trial assemble then have the solid one made the required thickness

Regards
John

[bsa-bill]

Not if they are clamped between the web and the bearing by the nut

of course

[RichardL]

Hey guys,

What should be the maximum allowed shim stack thickness? The machine shop I used did not dress down the PB bushing shoulder when they installed and honed the bushing I provided. The  shoulder was thicker than the previous composite bushing and the crank wouldn't turn. They've now machined it.down to what is supposed to be the original thickness, but the play feels like 0.050" now, vs 0.037" previous. I suppose it's my fault for not actually specifying the play to them. Haven't actually measured it yet, as I am sitting at lunch on the way home from the shop.

Richard L.

[trevinoz]

Richard,
                    At that thickness I would be inclined to machine a solid spacer to almost that dimension and go from there.
That seems an excessive amount of end float. Has the drive side been machined?.
Was the engine running with 0.037" float previously? That's excessive also.

Trev.

[RichardL]

Trev,

Thank you. As they say, "on further review" (and a full stomach) it appears that the non-shimmed float is about 0.037" or 0.038". I've yet to try to be real exact with it, but this measurement makes sense, since the machinist took the bush down to the height of the previous part. I'm guessing that an 0.035" or 0.036" stack behind a bearing fixed with Loctite will be secure. Correct me if you think me wrong.  I had a thought about adding the same type of Loctite between the shims to create a quasi-solid piece, but decided that it would be hard to estimate the effect of the Loctite on thickness and too late to do anything about it once applied.

I made a mistake by not telling the machinist to just shave the bush (it's accurate tech talk, don't blame me) by about 0.015" to require a shorter stack.

Richard L.

[muskrat]

G'day Richard. I've never had to use more than about 10 thou of shims. I'd say others have had more, but I'd be checking the rods are central in the bores. The thrust face of the bush is from memory 125 thou thick and this is the datum point. If it has been skimmed thinner the rods will be offset in the bores by that amount. To rectify shims would need to be placed under the bush.
I'd be interested in hearing how much shim was needed after a bush replacement by others here. I've probably only ever done a dozen or so.
Cheers