Topic: Need Crank Bearing Advice

[bunghole]

I hate to be a pest, but I would really appreciate some advice.  I'm planning on replacing the crank bearings with 5 new sets of green.  Here is a copy of the original post:

I spent tonight on the crankshaft bearings.  This is completely new territory for me, so I could use help and input.

My first step was to try and decipher the chicken scratch on the crankshaft ("chicken make lousy housepet").  Here is what it looked like to me:

"OKAAAAA   V44-S4"

On the case, it was easy to read and is "BBBBB"

According to the Clymer, the stock crank bearing should have been all green.

Next step was to measure the journals with a dial caliper (in mm):

1: 35.941
2: 35.992
3: 35.966
4: 35.941
5: 35.941

So for fun, I broke out the mics and measured again:

1: 35.994
2: 36.010 (not likely)
3: 35.989
4: 35.987
5: 35.989

Final step was to use the plasticgauge (clearances in mm).  Pics first and then measurements:

Virgin Plasticgauge waiting to be squished:



Squashed!!!:



1: 0.076
2: 0.102
3: 0.152
4: 0.127
5: 0.076



I should note that I didn't install of the crankcase bolts both top and bottom.  Most of them, especially near the crank, but not all the little ones.  Will that throw off my results?

If not, please divine what I need as far as replacement bearing inserts.  Clymer states that max clearance is 0.08 mm, so I according to that I need to replace 2,3, and 4 inserts.

[goon 1492]

I would go ahead an replace 1 and 5 too, even though they are not out they are .004 away from it, and .004 is the thickness of a sheet of notebook paper.

[bunghole]

Thanks Goon.  That's what I'm planning on doing.

So should I buy the green (that I believe were what was on there originally) under the assumption that the bearings are worn down and then plastigauge the new ones?  Or should I go the next size down (up?).

[scondon]

Thanks Goon.  That's what I'm planning on doing.

So should I buy the green (that I believe were what was on there originally) under the assumption that the bearings are worn down and then plastigauge the new ones?  Or should I go the next size down (up?).

  No way to know until you plastigauge the new ones Bwaller lent me two sets of new bearings and I swapped them into the 5 locations for measuring(measure 1/5, swap/retorque,measure 2/4, swap/retorque, measure#3). You can buy the three greens and measure all five spots with them.

I should note that I didn't install of the crankcase bolts both top and bottom.  Most of them, especially near the crank, but not all the little ones.  Will that throw off my results?

  Just the large bolts that hold the crank need to be torqued for measuring. 10 or 12 of 'em, I can't remember.

[markjenn]

Good for you for attempting this repair.  I've never done it, so take everything below with this in mind.

I'd be extremely conservative and replace any bearing insert that is not within new spec.  According to the shop manual, new spec is .02-.046mm.  I'd also put in all the bolts covered in the manual and do the proper sequence during the test fittings - it appears you're supposed to do the central 8mm first in sequence, then do the 6mm outside ones where the sequence doesn't appear to be important.

Are you going to use any gasket sealer or the "thread trick" to better seal the case halves?  I've heard conflicting reports about what's best here and I wonder if a dry assembly vs. a wet assembly would affect the plastiguage results.

Funny you can't better get a better match with the chicken scratching.  It's supposed to be JL-XXXXX for the crankshaft journals (X is A, B, or C) and PL-NNNN for the crankpins (N is 1, 2, 3, 4, 5).   The L indicates from the left or right, but I don't know if they're all L or not.  The J and P fixed characters are circled, it appears.  If your crankcase are B's, then your only worry appears to be if the crankshaft is a C which requires a brown rather than green bearing.

I can scan the official shop manual pages for you if you're worried about Clymer accuracy.

Good luck!

- Mark

[scondon]

I'd be extremely conservative and replace any bearing insert that is not within new spec.  According to the shop manual, new spec is .02-.046mm.  I'd also put in all the bolts covered in the manual and do the proper sequence during the test fittings - it appears you're supposed to do the central 8mm first in sequence, then do the 6mm outside ones where the sequence doesn't appear to be important.

 This is for re-assembly. For measuring, only the 8mm are necessary but ALL bolts can be torqued down if it makes one feel better about the job.

Are you going to use any gasket sealer or the "thread trick" to better seal the case halves?  I've heard conflicting reports about what's best here and I wonder if a dry assembly vs. a wet assembly would affect the plastiguage results.

 Measure VERY dry or plastigauge won't stick. Assemble "wet".



   When installing the crank I got back from APE I used Black shells(thickest available) and some of the gaps were still at the Honda wear limit and none were at the new bearing spec(ended up with .05 -.08 clearances). Something to do with the "micro polishing" of the crank journals when the crank work was done, i guess. 15,000 hard miles and nothings gone sloppy on me yet. I'd go with getting as "perfect" as possible, just posting this in case "perfect" is not attainable.

[markjenn]

Measure VERY dry or plastigauge won't stick. Assemble "wet".

Sorry, didn't make the question clear.  What I meant was whether you applied any gasket sealer between the case halves when you did the plastigauge measurement.  I would assume you wouldn't, but then if you used sealer in the final assembly, could this change the bearing clearances?

Also, a long time ago, I heard that the hot ticket for ensure a leak-free case-halve seal was to lay a fine thread down the parting seam as a last defense against any case imperfections.  Again, I wonder if that would affect the plastiguage accuracy.  Perhaps this is not done anymore.

- Mark

[scondon]

Measure VERY dry or plastigauge won't stick. Assemble "wet".

Sorry, didn't make the question clear.  What I meant was whether you applied any gasket sealer between the case halves when you did the plastigauge measurement.  I would assume you wouldn't, but then if you used sealer in the final assembly, could this change the bearing clearances?

Also, a long time ago, I heard that the hot ticket for ensure a leak-free case-halve seal was to lay a fine thread down the parting seam as a last defense against any case imperfections.  Again, I wonder if that would affect the plastiguage accuracy.  Perhaps this is not done anymore.

- Mark

Gotcha Certainly something to ponder. I would guess that sealant would not affect the inner bearings, since none is applied near them and that any difference liquid sealant would make to the case edges would not be of consequence.

 Quite a few people here lay down a bead of sealant before assembling. Myself included

[754]

Every mating surface on the cases should have thin layer of sealant, if not false reading or the case is being distorted.

 Everyone I took apart (76 or earlier) had sealant from the factory on the mating surfaces.. so yes put it on all the bearing pads.


The sealant I saw on them was a brownish colour, a bit like a coffee stain color...

[scondon]

Every mating surface on the cases should have thinlayer of seal;ant, if not false reading or the case is being distorted.

 Everyone I took apart had sealant from the factory on the mating surfaces.. so yes put it on all the bearing pads.

  What does the factory sealant look like? haven't found any on the '78's I've disassembled.

[harald]

I have assembled 5 engines until now and my advice is replace the crank bearings with the thickest you can get (blacK) and torque the bolts until specs or so the crank turns freely. Keep it simple. I am talking about engines who have gone at least 30000 miles. Less than that I would not replace the bearings unless damaged. The damaged ones would be replaced with the same color (or what I have )

[bunghole]

Every mating surface on the cases should have thinlayer of seal;ant, if not false reading or the case is being distorted.

 Everyone I took apart had sealant from the factory on the mating surfaces.. so yes put it on all the bearing pads.

  What does the factory sealant look like? haven't found any on the '78's I've disassembled.

I don't know if it was factory for sure, but my cases had a rubbery brown sealant in there.

[scondon]

Thanks guys. Going to be rebuilding a '71 motor this fall so want to follow the guidelines of that era

[Big Jay]

I'd be extremely conservative and replace any bearing insert that is not within new spec.  According to the shop manual, new spec is .02-.046mm.  I'd also put in all the bolts covered in the manual and do the proper sequence during the test fittings - it appears you're supposed to do the central 8mm first in sequence, then do the 6mm outside ones where the sequence doesn't appear to be important.

 This is for re-assembly. For measuring, only the 8mm are necessary but ALL bolts can be torqued down if it makes one feel better about the job.

Are you going to use any gasket sealer or the "thread trick" to better seal the case halves?  I've heard conflicting reports about what's best here and I wonder if a dry assembly vs. a wet assembly would affect the plastiguage results.

 Measure VERY dry or plastigauge won't stick. Assemble "wet".



   When installing the crank I got back from APE I used Black shells(thickest available) and some of the gaps were still at the Honda wear limit and none were at the new bearing spec(ended up with .05 -.08 clearances). Something to do with the "micro polishing" of the crank journals when the crank work was done, i guess. 15,000 hard miles and nothings gone sloppy on me yet. I'd go with getting as "perfect" as possible, just posting this in case "perfect" is not attainable.

Micro polishing removes nothing from the journal. People have sent us cranks and asked us to polish them down a bit for more clearance, and we have to explain to them that iot can't be done. If we have to take a few tenths off of a journal, it has to go in the crank grinder.  The reason some of these cranks may be close to being out of spec might have something to do with them being 35 years old

[scondon]

 

I'd be extremely conservative and replace any bearing insert that is not within new spec.  According to the shop manual, new spec is .02-.046mm.  I'd also put in all the bolts covered in the manual and do the proper sequence during the test fittings - it appears you're supposed to do the central 8mm first in sequence, then do the 6mm outside ones where the sequence doesn't appear to be important.

 This is for re-assembly. For measuring, only the 8mm are necessary but ALL bolts can be torqued down if it makes one feel better about the job.

Are you going to use any gasket sealer or the "thread trick" to better seal the case halves?  I've heard conflicting reports about what's best here and I wonder if a dry assembly vs. a wet assembly would affect the plastiguage results.

 Measure VERY dry or plastigauge won't stick. Assemble "wet".



   When installing the crank I got back from APE I used Black shells(thickest available) and some of the gaps were still at the Honda wear limit and none were at the new bearing spec(ended up with .05 -.08 clearances). Something to do with the "micro polishing" of the crank journals when the crank work was done, i guess. 15,000 hard miles and nothings gone sloppy on me yet. I'd go with getting as "perfect" as possible, just posting this in case "perfect" is not attainable.

Micro polishing removes nothing from the journal. People have sent us cranks and asked us to polish them down a bit for more clearance, and we have to explain to them that iot can't be done. If we have to take a few tenths off of a journal, it has to go in the crank grinder.  The reason some of these cranks may be close to being out of spec might have something to do with them being 35 years old

     Certainly just a "guess" on my part Jay. Too many variables to reach any valid conclusions on my part with just one crank. So I sent ya another

 Think it will be done soon? I'm prepared to use Falicons since the "chrome moly" rods don't seem to be panning out at the moment. Maybe by the time my next motor is on the stand

[Big Jay]

All of the Honda 750 cranks in house will be shipping on Thursday the 17th.

Thanks

Jay