bearings clearence

i have this block that was perfectl fine except one rod was slightly bent witha leaky headgasket...got it apart and got the block cleaned up and im looking for another stock rod thats in good shape so i dont need to get all my rods resized...i got the crank and some standard bearings and put tit ogether plasticgauged it and came up with about .34 on most of the mains and i think the stock specks are .020-.030

i know its close but what are you guys opinion? should i have the crank turned then oversize bearings? id rather not the cars just goana be a cam only car with little nitrous, not really a street car but will see some mileage driving to the track and such

If you are looking to reduce clearances a bit, you can either get another set of .001 over bearings and use half/half to get the clearance you want or you can buy a nice set of coated bearings which tighten up the clearances a few thou.

I t would be fine IMO but you really can't rely on plastigauge......

Like he said you can mix em up and get them right. OR do the coated ones

But if all others are .0030 and one is .0034 I would fix it, but saying its .0034 with plastigauge doesen't say much

There's a problem if you are getting .0034" clearance - stock these motors run .0012" - .0024" so you have a worn crank. Plastigauge is not the right way to measure clearances.

You need to take your components in to the machine shop and have the measured properly, especially if you are going to race/spray it.

whats wrong with plasticgauge???

and the thing is this motor was running pefrectly fine when it came outa a 94z with 170k on it...we pulled it to refresh it and put it back together...i would think with new bearings it woulda tightened it up more...how else could i get it checked thats "mmore reliable"

a mic. is the only way to get a true measurement

I read an article in Hot Rod or Car Craft Magazine, where they compared plasti-gauge to a micrometer. Plasti-gauge almost always gave a reading of twice the clearance that was ACTUALLY there.

So divide by 2. It has the opposite side pulled up against the journal.



David

LOL! So you think when someone has .0025 clearance that there is .0025 ALL the way around the journal?!




I do wanna know how the thread starter got .0034 with plastigaue! :)

coated bearings.

whoops well the motor in my car now has within spec on plaster gauge it has 35 psi at idle and 80+ at wot its got 15k on it now

it was i think .0022-.0024 on all the rods
think the mains were .0018-0020 and 0024 on #5

if yall are sayin half of this that means the mine were way too tight....


anyways i read some threads about getting undersized or oversized bearings by 0001 and using one half of it to tighten them up some....so would i need -.0001 or + to tighten it up
the crank and rods and mains all came outa the motor fine...im goana get a mic i recheck but if i still need to tighten them up can i just get oversized bearings

It seems odd, but what you want are called undersize bearings, because they are thinner than a standard bearing. If you need to mix bearing sizes, put the more undersized half on the bottom (in the cap). I disagree about Plastigage - it is accurate but not as precise as using instruments. It has an advantage in that you are measuring the clearance of the assembled part. Also, while the ultimate precision is less than using mikes, it is easier to achieve. IOW, mikes are hard to use correctly, Plastigage is easy. Have you calibrated your instruments recently?

Rich

LOL! So you think when someone has .0025 clearance that there is .0025 ALL the way around the journal?!




I do wanna know how the thread starter got .0034 with plastigaue! :)


JUst repeating what I had read. I was mistaken, I am getting old, the clearance was 1/2 of what the Mic said it had.


Here ya go

http://www.carcraft.com/techfaq/116_0701_plastigage_vs_micrometer/index.html


http://www.carcraft.com/techfaq/116_0701_plastigage_vs_micrometer/photo_04.html
David

A problem that I had when building my current motor pertaining to plasti-gage, was the rods twisting when I torqued them down, which seemed to give me a "tighter than actual" measurement. I was using an X bearing, which is .001 OVERsized and gives you an extra thousandth of clearance and was still getting ~.018 on the rods. I finally took the feeler gauges that I had used to check side clearance, put them between the rods to hold them straight, and PRESTO... .0022 rod clearance! :)

Probably the same problem they are having on that rod journal in the link you supplied.

A problem that I had when building my current motor pertaining to plasti-gage, was the rods twisting when I torqued them down, which seemed to give me a "tighter than actual" measurement. I was using an X bearing, which is .001 OVERsized and gives you an extra thousandth of clearance and was still getting ~.018 on the rods. I finally took the feeler gauges that I had used to check side clearance, put them between the rods to hold them straight, and PRESTO... .0022 rod clearance! :)

Probably the same problem they are having on that rod journal in the link you supplied.

Good thinking on your part.

I knew something wasn't right and had to keep 'em straight somehow! :)

i double checked it and i hink they will be fine the rods were all about .0014-15

the mains were 1-3 .0015 4.002 5.003

5 is loose but i think it wil be fine....think were goana put it together like this....

Plasti gauge is what we were taught to use in college. Our intructors felt that measing the assembled engine was more important that using micrometers.

rskrause:> Isn't an undersized bearing thicker to make up for the extra clearance. If I am not mistaken the name comes from the fact the crank journals are undersized and not the bearings. Correct me if I am wrong.

Plasti gauge is what we were taught to use in college. Our intructors felt that measing the assembled engine was more important that using micrometers.

rskrause:> Isn't an undersized bearing thicker to make up for the extra clearance. If I am not mistaken the name comes from the fact the crank journals are undersized and not the bearings. Correct me if I am wrong.

Yes, that was what I was trying to say. Sorry. It sounds backwards (my point) which I then proceeded to be caught up by. DOH.

Rich