318 bearing clearances
- Thread starter FlwSock
- Start date
dvw
Well-Known Member
.001"/ inch of journal diameter. Did it spin a main or a rod? was is line honed or was the rod replaced?
Doug
Doug
FlwSock
Member
It spun a rod bearing. Everything was fresh from the machine shop. We think the problem came from me putting the spiro-locks in the piston. After destroying the bearing, I took it to my machinist and he said that the spiro-locks are not correct for my application, didn't allow the wrist pin the slop it needed, and therefore the rod tried to walk on the crank and therefore spun a bearing.
dvw
Well-Known Member
I do not agree. The pin should not have any slop, spec should be roughly .001". I hope you swapped the rod.
Doug
FlwSock
Member
I think you're misinterpreting what I meant to say. I mean the piston should be able to slide back and forth on the wrist pin. The pin itself isn't josseling around in the piston head or anything like that, but rather the piston is able to now slide on the wrist pin back and forth a little bit. I didn't swap the rod, I had it fixed at the shop.
As a separate question, while installing the new rod bearings, one of the new ones had a slight nick in it, straight out of the packaging. It's probably about 1-2mm long, and is only broke through the first layer of bearing material (you can feel the indent with your finger). Does this warrant me going back to the shop and getting new ones, or will it be fine? I'd hate to have to take this motor out again because the tiny nick messed everything up, but the shop is also an hour from me. If it's not a big deal I'll just leave it in. If it will cause problems, I have no issue taking it out.
miller
Well-Known Member
Worth an hour, to make it right? Nicked 'new' bearing...no good.
Say you had the rod fixed? That depends. Fitting bearings into a split rod, you want two things. First, of course, correct clearance between the bearing and journal. But, especially since that hole has been messed with, all in the same breath, you should get the 'pinch' the bearing halves need to lock in.
I do a dry fit on mine, putting the bearings into the rod, put the cap in place, and just tighten the rod bolts until snug. All you want is for things to seat. Then hold the rod up to the light...bearing halves should be together, but a very slight gap between the rod and cap. If I can see ANY light, and the gap is less than .001, it's good. When the rod bolts are torqued, that gap closes, lightly pinching the bearing halves together, locking the bearing into place in the rod.
If the bearing halves are not locked in...can spin. For what it's worth.
Say you had the rod fixed? That depends. Fitting bearings into a split rod, you want two things. First, of course, correct clearance between the bearing and journal. But, especially since that hole has been messed with, all in the same breath, you should get the 'pinch' the bearing halves need to lock in.
I do a dry fit on mine, putting the bearings into the rod, put the cap in place, and just tighten the rod bolts until snug. All you want is for things to seat. Then hold the rod up to the light...bearing halves should be together, but a very slight gap between the rod and cap. If I can see ANY light, and the gap is less than .001, it's good. When the rod bolts are torqued, that gap closes, lightly pinching the bearing halves together, locking the bearing into place in the rod.
If the bearing halves are not locked in...can spin. For what it's worth.
FlwSock
Member
The rod was slightly machined to get rid of the scarring from the spun bearing and honed out. All of the rods are now fitted with correct sized bearings, and all the crank journals were ground again to keep everything uniform. I'll be going out there in an hour or so to take everything off and completely restart. I'll update with progress tonight. Thank you all for your help so far!
dvw
Well-Known Member
FlwSock
Member
Update:
Yesterday I took the bearing to the machine shop and he said he didn't like the way it was either. I will be getting a new one. After taking out all the brand new rod bearings I had just put in a few days ago, almost half of them were scarred up. I'm not sure how this happened, maybe from smacking them too hard trying to get the caps off? I'm not sure. Regardless, I will now be getting all new rod bearings again. The mains were still good, and all checked out at about .0015in. Some of them were just a hair tighter at ~.0013. That should be ok, shouldn't it? I understand plastiguage isn't perfect, and even if it was, .0002 variance shouldn't cause a problem, right?
Yesterday I took the bearing to the machine shop and he said he didn't like the way it was either. I will be getting a new one. After taking out all the brand new rod bearings I had just put in a few days ago, almost half of them were scarred up. I'm not sure how this happened, maybe from smacking them too hard trying to get the caps off? I'm not sure. Regardless, I will now be getting all new rod bearings again. The mains were still good, and all checked out at about .0015in. Some of them were just a hair tighter at ~.0013. That should be ok, shouldn't it? I understand plastiguage isn't perfect, and even if it was, .0002 variance shouldn't cause a problem, right?
dvw
Well-Known Member
For a performance engine .0015" is pretty tight. Street use would be fine. Damaged bearings are either high spots on the crank, or more likely dirt.
Doug
Doug
miller
Well-Known Member
As long as that .0013-.0015 is in the book limits, it should go. Snug, for my liking, prefer at least .002 (but I'm a BB guy). Just consider that clearance is just over .0005 per side.
Gotta be 'gentle' with those bearings. They get slapped around enough, as it is!
Gotta be 'gentle' with those bearings. They get slapped around enough, as it is!
FlwSock
Member
It is a performance engine that will see the strip very rarely, but will probably be driven hard on the street. Rev limiter will be set at 6100RPM. More of a take off from a dig quick and get going. I just turned 22, so you guys know how it'll be lol. All said, it's a heavily modified street machine.
From what people have told me the main should be .0015 to .0025. Does the .0002 warrant me calling the machine shop and discussing my options, or can it be chucked up to plastiguage just not being perfect and it's probably fine? Like I said before, it'll be driven hard.
For reference, it's an NA engine with:
Extensive headwork done to magnum heads
Bored .3 over
Different springs for the big cam
LA Cam fitted with spacer to work with magnum block with .574intake/.569ext lift
RPM Airgap Intake
Holley 650 double pumper
stock rods
I'm assuming it probably makes ~430hp but that's just a guess.
From what people have told me the main should be .0015 to .0025. Does the .0002 warrant me calling the machine shop and discussing my options, or can it be chucked up to plastiguage just not being perfect and it's probably fine? Like I said before, it'll be driven hard.
For reference, it's an NA engine with:
Extensive headwork done to magnum heads
Bored .3 over
Different springs for the big cam
LA Cam fitted with spacer to work with magnum block with .574intake/.569ext lift
RPM Airgap Intake
Holley 650 double pumper
stock rods
I'm assuming it probably makes ~430hp but that's just a guess.
Last edited:
Hemirunner
Well-Known Member
What assembly lube are you using and how clean is the assembly area? Given the journal size, application and power level, I would prefer .0025 but .0020 will probably be sufficient.
FlwSock
Member
When I did the clearances, I did it with no lube and as clean as I could get it. The crank may have had a thin layer of oil on it yet, but I doubt it. The area was clean to the best of my ability. After I did the clearances I took it all apart, lubed it all up and installed them. I'm using Sta-Lube assembly lube with moly-graphite.
dvw
Well-Known Member
Like stated before. Minimum on a performance motor is generally .001" per inch of pin diameter. That would put you at .0021" rod, .0025" mains. A little looser won't hurt it. If the the rods egg shape at all or oil film gets thin if you're at .0015" it could be trouble. Remember; if you have extra bearing clearance you will know, too little and everyone will know.
Doug
Doug
dvw
Well-Known Member
Is the line bore correct? Rod bore correct? If so .001 rod bearings are available. Also Clevite H series have more clearance than Clevite P series. What bearings do you have now?
Doug
miller
Well-Known Member
What size bearings are you using? Standard...undersize?
Similar threads
- Locked
