Author Topic: Crankshaft Shim Question  (Read 126 times)

Offline Happyhenry

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Crankshaft Shim Question
« on: 17.11. 2020 17:26 »
Hello,

I'm in the process of rebuilding a 1948-ish bottom end from a "complete" engine, two dismantled part-engines and several more bits...

When I dismantled the "complete" engine I found a small stack of shims between the drive-side ball bearing and the crank web, but also a shim with a much larger outer diameter between the bearing and the crankcase. i.e. outside the bearing.

As these engines have no oil seal between crankcase and primary drive I assume that this larger 'shim' acts as a seal to prevent crankcase pressure fully evacuating into the primary drive void through the bearing.
 
However, I can't find this part on any of the parts diagrams or lists.

Am I imagining things, or should it not be there?

Cheers
H
"Every time he put his key in the door he wondered what he was letting himself in for." - Spike Milligan - Puckoon.

Offline Swarfcut

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Re: Crankshaft Shim Question
« Reply #1 on: 17.11. 2020 17:58 »
  Hi Henry. You are correct, it should be there. It is trapped between the crank and drive sleeve, and rotates with the crank.
         From your description you have an early Longstroke engine, later developed so called shortstroke design has a roller bearing. The shim you describe is part 67 389 *and although listed as a shim, is more of an oil slinger. It was also used on the later engine until the advent of the oilseal design change, and so can be seen in 1949-53 parts lists. These earlier engines don't have an oilseal, but the drive sleeve has a grooved periphery to act as a scroll to hold back the oil. Having said that, many engines are found with a smooth edge drive sleeve, identical to that used with the seal. Your hole in the case where the drive sleeve goes should be a close fit to the sleeve edge.

 Out of interest, did the ball race stay on the crank or in the case? The later design is certainly easier to pull apart, but having a ball race avoids the usual hassle of setting the crank end float to the fine limit required on the later engine.

 Plenty about this shim on the Forum, just a case of going back thro' previous posts. Parts catalogues are also listed in the Literature Section of the Forum.

 Swarfy


 * Typo Error  Should be 67-349

Offline Happyhenry

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Re: Crankshaft Shim Question
« Reply #2 on: 18.11. 2020 08:22 »
Thanks Swarfy,

The part shown in the books (1949-1953) that I have is shown as 81... 67-349 "Bearing Shim (Drive Side)" followed by 82... 67-2056/7/8 "Engine Sprocket Distance Piece".
I can't find 67-0389.

It's hard to tell from the exploded view, but I guess that the "Bearing Shim" is the slinger inside the cases between the bearing and the case, and the "Engine Sprocket Distance Piece" is outside the case.

The bearing stayed on the crankshaft when I dismantled the engine and was a swine to get off. I also have a couple of dismantled engines and one has the bearing in the case, the other is on the crankshaft.

What fills me with dread as to how I'm going shim the crank for end play if I have to risk destroying a bearing every time I have to remove it to add a shim. There must be a better way...

H
"Every time he put his key in the door he wondered what he was letting himself in for." - Spike Milligan - Puckoon.

Offline Happyhenry

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Re: Crankshaft Shim Question
« Reply #3 on: 18.11. 2020 08:50 »
I have just found the 'shim thread' "A7 46-50 Long Stroke / Bearing Shim Drive Shift A7 1948" and my shim, that is outboard the bearing but inside the crank case, is the same plain shim as in Trevinoz's photograph in the thread. I'll have to check whether I have a scrolled cushdrive bearing in my boxes of bits.

My shim is not the same as the slotted shim 67-349 in the parts book.

I've saved my old shim, but it's a little wobbly. Perhaps I'll make another out of shim stock as they are obviously now unobtainable.
"Every time he put his key in the door he wondered what he was letting himself in for." - Spike Milligan - Puckoon.

Online KiwiGF

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Re: Crankshaft Shim Question
« Reply #4 on: 18.11. 2020 09:05 »
Thanks Swarfy,

The part shown in the books (1949-1953) that I have is shown as 81... 67-349 "Bearing Shim (Drive Side)" followed by 82... 67-2056/7/8 "Engine Sprocket Distance Piece".
I can't find 67-0389.

It's hard to tell from the exploded view, but I guess that the "Bearing Shim" is the slinger inside the cases between the bearing and the case, and the "Engine Sprocket Distance Piece" is outside the case.

The bearing stayed on the crankshaft when I dismantled the engine and was a swine to get off. I also have a couple of dismantled engines and one has the bearing in the case, the other is on the crankshaft.

What fills me with dread as to how I'm going shim the crank for end play if I have to risk destroying a bearing every time I have to remove it to add a shim. There must be a better way...

H

Have you read about modifying the old bearing to fit easily on the shaft and to use that to get the shims right?
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Offline Happyhenry

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Re: Crankshaft Shim Question
« Reply #5 on: 18.11. 2020 13:12 »
Have you read about modifying the old bearing to fit easily on the shaft and to use that to get the shims right?[/quote]

No, not read anything, but it's something I have thought about as I have three old bearings. Just need to ensure that one is the same width, or a known difference, to the new one.

The cases are away being vapour blasted and the crank is ready for a regrind to the big ends (-30) and the timing-side bearing journal (-10), but I want to make sure that I have the new shells and journal bearing first.

Draganfly's site says that the ball and the roller bearings are interchangeable, but I've also been told that they are not.  *dunno*
"Every time he put his key in the door he wondered what he was letting himself in for." - Spike Milligan - Puckoon.

Offline Swarfcut

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Re: Crankshaft Shim Question
« Reply #6 on: 18.11. 2020 14:02 »
 Henry.
      Apologies, the slinger shim part is item  81 in the book, 67- 349, I miss - typed and failed to review prepost closely enough.  You are correct in your interpretation of the diagram. So you have the remains of something, whether an original part or someone else's codge.
 
 The bearing sizes are different, Longstroke is an Imperial size, later engine is a Metric size. The ball race design ensures there is no float when everything is tightened up, but the crank needs a few thou for expansion. The only way this could be accurately estimated is with a feeler gauge between crank and timing bush face, well nigh impossible, or the inner race being a sliding fit on the crank, being a more sensible solution for easy re-assembly.  All this is already detailed on the Forum.

 Swarfy.