Topic: Question about rod and main bearings.

[Artfrombama]

Reading the charts, bearings are sized by the bore of the case or rod and the crank journal diameter.

My dilemma is the dimensions and the markings don't jive... For instance the rods are marked "2" but when I measure they actually are a "1".
Same with the crank, etching on the crankshaft is measured 4444 but when I measure it's actually 5555.

Gettin ready to order bearings and don't know which ones to order. Order by actual size or by factory markings?
Has anyone else run into this and WTF did you do?

[Tim2005]

Go by the actual sizes, imo the best bet is to plastiguage every bearing.

[Jerry Rxman Griffin aka MuthaF'er]

+1 and Plastigauge them. Best starting point. Your tools and hands and eyes aren't the same ones that originally measured them. You may need to buy a few more but there's always needy guys here that would take your extras off your hands.

[Artfrombama]

+1 and Plastigauge them. Best starting point. Your tools and hands and eyes aren't the same ones that originally measured them. You may need to buy a few more but there's always needy guys here that would take your extras off your hands.

Yea, but I'm the needy guy!

[mystic_1]

How are you taking your measurements?  i.e. what tools and processes are you using?

Your stated numbers on the rods suggest that the holes are SMALLER than expected, and the journals are LARGER than expected.

You might expect the journals to be SMALLER than marked, due to wear, but they're unlikely to have actually grown and I 've never heard doubts as to the accuracy of the original markings.

The holes in the rods should in theory never change size, since all the wear is taken up by the bearing shell.


mystic_1

[Artfrombama]

How are you taking your measurements?  i.e. what tools and processes are you using?

25-50mm micrometer and telescopic (snap) gauge.

Your stated numbers on the rods suggest that the holes are SMALLER than expected, and the journals are LARGER than expected.

Rods are marked "2" which according to the chart should be 39.008-39.016mm.
When miked the rod bore was actually 39.02-39.03mm which should be marked "1".

Crankshaft is marked "4" which should be 35.995-35.990mm.
Measures 35.98-35.99mm which is indicated in the chart to be "5"

You might expect the journals to be SMALLER than marked, due to wear, but they're unlikely to have actually grown and I 've never heard doubts as to the accuracy of the original markings.

The holes in the rods should in theory never change size, since all the wear is taken up by the bearing shell.


mystic_1

Unless someone has a definite answer I suppose I'll just order two sets (yellow and green) of bearings and open only one set to measure with, then return what I don't need.

[Jerry Rxman Griffin aka MuthaF'er]

Special orders are probably not returnable as no dealer will want these on their shelves.

I may have some unused yellow mains if you want to just start with the greens. $10 each if so.

Best bet is to match the letters/numbers and confirm with Plastigauge.   

[mystic_1]

OK, so the journals are actually _smaller_ than marked, which is at least plausible.

Your measurements indicate that currently you have (39.02 - 35.98) = 3.04 mm difference between the holes.

Yellow inserts (the thinnest) are 1.490 to 1.486  mm thick, average out to 1.488 and multiply by two shells and that gives us 2.976 mm.

Subtract that from your measured clearance and that leaves 0.064 mm

The maximum service limit is 0.08mm, so yellow bearings would put you inside that still, but the standard clearance is 0.02 to 0.046 mm and yellow bearings would put you outside that.



Green inserts are 1.494 to 1.490 thickness, average to 1.492, multiply by two gives us 2.984 mm, leaving 0.056 mm clearance, still too big.

Brown inserts are 1.498 to 1.494, average to 1.496, doubles to 2.992, leaving 0.048mm clearance, just barely outside standard tolerance. 

Black inserts are 1.502 to 1.496, agerage to 1.499, double to 2.998, this would leave 0.042 mm clearance, this would be within standard clearance.



Really given your numbers, any of the above would run, but it looks to me like you should be putting in Black inserts based on the clearances you're observing.

mystic_1

[Artfrombama]

OK, so the journals are actually _smaller_ than marked, which is at least plausible.

Your measurements indicate that currently you have (39.02 - 35.98) = 3.04 mm difference between the holes.

Yellow inserts (the thinnest) are 1.490 to 1.486  mm thick, average out to 1.488 and multiply by two shells and that gives us 2.976 mm.

Subtract that from your measured clearance and that leaves 0.064 mm

The maximum service limit is 0.08mm, so yellow bearings would put you inside that still, but the standard clearance is 0.02 to 0.046 mm and yellow bearings would put you outside that.



Green inserts are 1.494 to 1.490 thickness, average to 1.492, multiply by two gives us 2.984 mm, leaving 0.056 mm clearance, still too big.

Brown inserts are 1.498 to 1.494, average to 1.496, doubles to 2.992, leaving 0.048mm clearance, just barely outside standard tolerance. 

Black inserts are 1.502 to 1.496, agerage to 1.499, double to 2.998, this would leave 0.042 mm clearance, this would be within standard clearance.



Really given your numbers, any of the above would run, but it looks to me like you should be putting in Black inserts based on the clearances you're observing.

mystic_1

Thanks a lot mystic_1, the markings not jiving with the measurement, then my inches brain trying to deal in mm just had my brain twisted.
I re-confirmed your data and have ordered black bearings.

[Artfrombama]

The black rod bearings put the clearance right at .0015". Close enuf!

[mystic_1]

0.0381 mm, not too shabby!

mystic_1