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LT1-LT4 Modifications
1993-97 Gen II Small Block V8

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Old 05-09-2013, 06:43 AM   #1
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Default Rod bearing clearance between .0015 and .002 too tight?

I am building a 385 with forged Eagle crank, Scat 6" rods and Clevite H bearings, I am checking the rod clearance with plastigage and the first time I oiled the bearings with 15w40 and got pretty consistent .0015" clearance with plastigage, tried again after cleaning bearings and crank and got between the .0015" and .002" mark. Is this too tight or is it ok? The crank turns perfectly by finger (machine shop setup the crank clearance when filing my rings) and when putting rods/pistons on without rings it turns just as easily. I tried using a digital micrometer to measure the rod journal vs rods/bearings and got .002 although I know that's not as accurate as a dial bore gauge. Should this be ok with clearance or do I need more? It's a street/autox/RR car, cam makes power to about 6700.

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Old 05-09-2013, 07:41 AM   #2
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That is not an accurate way to do it, but if is correct I would call that too tight for a high RPM engine. On a big journal crank I use .025" for the rods, and ,003" for the mains.
I don't like the way a dial bore gauge marks my bearings. I have, for close to 50 years, used inside & outside mics. I use the inside mic for a gauge in the bearings, and measure it and the crank with the outside mic. Of course, the difference is your oil clearance. You can probably pick up a set of mics at a pawn shop. "Wiped out" bearings are most always caused right here.
Hope this helps.
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Old 05-09-2013, 08:40 AM   #3
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Quote:
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That is not an accurate way to do it, but if is correct I would call that too tight for a high RPM engine. On a big journal crank I use .025" for the rods, and ,003" for the mains.
I don't like the way a dial bore gauge marks my bearings. I have, for close to 50 years, used inside & outside mics. I use the inside mic for a gauge in the bearings, and measure it and the crank with the outside mic. Of course, the difference is your oil clearance. You can probably pick up a set of mics at a pawn shop. "Wiped out" bearings are most always caused right here.
Hope this helps.

Sounds too tight to me and I would never trust platigage on a performance motor. At the very least, get some telescoping guages and a micrometer which would bu under $75 at a discount tool store.

I would reccomend you take the short-block to a good engine builder and simply have him assemble the short block then you can finish it up. The short-block needs to be right the first time.
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Old 05-09-2013, 08:44 AM   #4
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Should I order a half set of CB663HXN bearings (-.001) and mix with my std CB663HN bearings to gain another .0005 to be safe?
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Old 05-09-2013, 09:25 AM   #5
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I have no problem assembling the rest myself as the machine shop setup the crank and rings already for me. I just want to get .002-.0025 clearance to be on the safe side.
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Old 05-09-2013, 05:16 PM   #6
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i would see if some one is local that can come check it the right way. and yes you can go to a hx bearing if needed. that's what i run.
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Old 05-09-2013, 07:31 PM   #7
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I have no problem assembling the rest myself as the machine shop setup the crank and rings already for me. I just want to get .002-.0025 clearance to be on the safe side.
Have you checked your mains yet? The machine shop that "set up your crank" may not do a lot of performance work and have your mains too tight too. Next time you have a crank ground tell them you want it on the low side. If they don't know what that means take it with you & find another shop. Too many guys appear to think all machine shops are equal. Not so. Standard rebuilds & performance & race engines are not the same. Avoid the shops that don't know the difference.
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9.91, 136.51, 1.38 60' (Spinning, usually 1.31), 1329' DA, foot braking it, NA 383" LT1, 4L60E, 3280 lbs, LT4 heads & intake, street legal.
Now 350" NHRA/IHRA SS/JA. Well, maybe it's not the SLOWEST on the planet: 9.88 @ 134.10, 1.260 60' (11.00 NHRA Index) But still not fast enough.
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Old 05-09-2013, 09:06 PM   #8
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It's a new crank, all parts are new actually, block was align honed, bored, decked, intake and heads setup, etc. The machine shop actually only does racing engines, Jeff Taylor Performance. When I installed the crank with std HN bearings at home it was hard to turn, so when I took the block and rings to have them gapped, i asked them to check my crank main clearance, and they ended up swapping out to HXN bearings because the std bearings were too tight, however I just forgot to ask them to measure my rod clearances as well when I picked everything up. The crank is setup great now, I can spin it with 3 fingers, and when I put a pair of rods and pistons torqued fully with oil on a journal, it turns just as freely, practicall no additional resistance than without the rods. They said I should setup the rods for .002-.0025 clearance, which is why I was asking about the plastigauge reading between .0015 and .002 when I measured dry.
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Old 05-10-2013, 05:04 AM   #9
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Quote:
Originally Posted by kgkern01 View Post
It's a new crank, all parts are new actually, block was align honed, bored, decked, intake and heads setup, etc. The machine shop actually only does racing engines, Jeff Taylor Performance. When I installed the crank with std HN bearings at home it was hard to turn, so when I took the block and rings to have them gapped, i asked them to check my crank main clearance, and they ended up swapping out to HXN bearings because the std bearings were too tight, however I just forgot to ask them to measure my rod clearances as well when I picked everything up. The crank is setup great now, I can spin it with 3 fingers, and when I put a pair of rods and pistons torqued fully with oil on a journal, it turns just as freely, practicall no additional resistance than without the rods. They said I should setup the rods for .002-.0025 clearance, which is why I was asking about the plastigauge reading between .0015 and .002 when I measured dry.
platigauge is like throwing a hotdog down a hall way in terms of accuracy. i would not use the "it spins freely buy hand so it must be ok" method.
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Old 05-10-2013, 07:05 AM   #10
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Quote:
Originally Posted by kgkern01 View Post
It's a new crank, all parts are new actually, block was align honed, bored, decked, intake and heads setup, etc. The machine shop actually only does racing engines, Jeff Taylor Performance. When I installed the crank with std HN bearings at home it was hard to turn, so when I took the block and rings to have them gapped, i asked them to check my crank main clearance, and they ended up swapping out to HXN bearings because the std bearings were too tight, however I just forgot to ask them to measure my rod clearances as well when I picked everything up. The crank is setup great now, I can spin it with 3 fingers, and when I put a pair of rods and pistons torqued fully with oil on a journal, it turns just as freely, practicall no additional resistance than without the rods. They said I should setup the rods for .002-.0025 clearance, which is why I was asking about the plastigauge reading between .0015 and .002 when I measured dry.
Well, you won't find a better machine shop! They build some very fast stuff!
It would be nice if you could get somebody to measure the rod bearing clearance properly.
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9.91, 136.51, 1.38 60' (Spinning, usually 1.31), 1329' DA, foot braking it, NA 383" LT1, 4L60E, 3280 lbs, LT4 heads & intake, street legal.
Now 350" NHRA/IHRA SS/JA. Well, maybe it's not the SLOWEST on the planet: 9.88 @ 134.10, 1.260 60' (11.00 NHRA Index) But still not fast enough.
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Old 05-10-2013, 07:49 AM   #11
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I run the numbers ed said on street/strip motors......
.025 rods and .030 mains.......for a street motor .0015 to .0020 isn't the end of the world its on the tight side but not horrible its within gm spec

my suggestion would be grab a set of "X" bearings they will loosen everything up about .001 you can always mix and match half shells to get .0005 if you want too I did this with my motor the last two rebuilds and have never seen any issues at all.....on a race motor like mine im running .0028-.0030 on my rods and .0030-.0033 on my mains and last time I had it apart after 3 years of 8000rpm abuse the bearings looked so good I wanted to re use them lol.... (I didn't ) ........also fyi plastigauge is a "close enough" tool IMO, good for a farm truck but out of place on performance builds
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Old 05-10-2013, 09:22 AM   #12
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I would buy four X bearings and run one X shell in each rod. That is what is in mine right now. If Jeff Taylor tells you a **** aunt will pull a freight train, just start figuring out how to hook that little sucker up. You are lucky to have a shop of that calibre close enough to do your work.
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9.91, 136.51, 1.38 60' (Spinning, usually 1.31), 1329' DA, foot braking it, NA 383" LT1, 4L60E, 3280 lbs, LT4 heads & intake, street legal.
Now 350" NHRA/IHRA SS/JA. Well, maybe it's not the SLOWEST on the planet: 9.88 @ 134.10, 1.260 60' (11.00 NHRA Index) But still not fast enough.
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Old 05-10-2013, 02:21 PM   #13
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Yeah it's a great shop, and only 10 min from my house, his customer service is awesome as well.

So with 4 sets of X bearings, do I still need to install them based on the 'upper' and 'lower' markings, or is installing them all on the cap side ok?
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Old 05-10-2013, 03:27 PM   #14
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People have told me they thought the X shell should go in the top. I have put them in both places and can not tell it makes any difference. I would just put them where they are marked.
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9.91, 136.51, 1.38 60' (Spinning, usually 1.31), 1329' DA, foot braking it, NA 383" LT1, 4L60E, 3280 lbs, LT4 heads & intake, street legal.
Now 350" NHRA/IHRA SS/JA. Well, maybe it's not the SLOWEST on the planet: 9.88 @ 134.10, 1.260 60' (11.00 NHRA Index) But still not fast enough.
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Old 05-15-2013, 10:05 AM   #15
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Installed the HXN bearings, re-plastigaged, and it seemed to give me the slightly over .002 I was looking for. Now I'm ready to assemble this beast!

PS, anyone want to buy 4 new CB663HN bearings? Lol
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Old 05-15-2013, 02:59 PM   #16
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I would hang on to them. If you ever have to go back into it later you already have half a set of rod bearings.
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9.91, 136.51, 1.38 60' (Spinning, usually 1.31), 1329' DA, foot braking it, NA 383" LT1, 4L60E, 3280 lbs, LT4 heads & intake, street legal.
Now 350" NHRA/IHRA SS/JA. Well, maybe it's not the SLOWEST on the planet: 9.88 @ 134.10, 1.260 60' (11.00 NHRA Index) But still not fast enough.
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Old 05-15-2013, 03:00 PM   #17
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Good point.
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Old 05-15-2013, 03:32 PM   #18
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Quote:
Originally Posted by Ed Wright View Post
Have you checked your mains yet? The machine shop that "set up your crank" may not do a lot of performance work and have your mains too tight too. Next time you have a crank ground tell them you want it on the low side. If they don't know what that means take it with you & find another shop. Too many guys appear to think all machine shops are equal. Not so. Standard rebuilds & performance & race engines are not the same. Avoid the shops that don't know the difference.
I had a shop cut the seats into the water jacket and then on another head they milled the heads with the valves on, that took a chunk out of the intake valve.
I asked them if they use BHJ plates or if they have master setting fixture. They said no on one and whats that on the other. I couldn't get out of that shop fast enough.
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Old 05-15-2013, 03:32 PM
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