I’m assembling my 396cc engine at the moment and have found a few things that are out of tolerance. This short block has previously run 8k miles and was built by Nu-Tek, but all parts look okay except the Cola main crank journals are slightly below what is allowed (journals to small) 2.4480".

How much rod side clearance is allowed?
In the repair manual it say .006”--.014”
Mine is using 6” Eagle H-beam rods and Cola 3.875” crank .022--.026”
Is this still okay and if not, how can I correct this???

I also measured the crank main bearing clearance and it’s way more than allowed; it's about at .0033". max. allowed .0028".
Does anybody know of any shop that purposely uses that much clearance for some reason??

I ordered a set of .001” undersize bearing, these should bring the clearance down to a normal range.

For any info I would be very grateful.
Arnold

 

Make sure you're measuring things but otherwise you are doing the right thing Arnold. Set bearing clearance and measure with the 1 bearings to close it up some and the rod side clrance is alright at .025 or so. They are usually arouns .020 to .026 anyway with those parts. If the cranks has been turned the journals might have been slightly widened but I am assuming you're still at normal size. Also check you're line hone and main cap torgue to make sure they didn't open up the housings excessively too?

 

I'm going to see if I can get the main clearance set to about .0023-.0027 by using only the upper half or both halfs of the undersize bearings. I've done this before on my 350cc 400 hp engine for all bearings and it works great, 15k miles so far. We do this at where I work, the largest engine plant in the world, on all engines. We have 4 different sizes for rod and main bearings and mix these accordingly.

The main bearings I used for measuring were new Federal Mogul std. 7081 CHBL / 522T.

The rod bearings are new Clevite 77 CB-663 H / 03C12CD1

Arnold

 

Yes we do that all the time on real race engines and street engines. I till work great.

 

Between the journal and bearing landing should be oil when operating. It's much better to have .003 than .0015 clearance (being a bit tight could be unforgiving). The two surfaces should never normally meet. Crank journals are ground then highly polished, burr-free and hardened in several ways. I cylindrically ground for years...it's all good....

 

Unfortunately, without swapping parts, you are pretty well stuck with the clearances you end up with. On a street engine, I prefer something closer to the manual recommendations. The larger the clearance, the greater the burden, that is put on the oil rings.

 

It took me some time to get all this info together. I asked the engineers of all of these manufacturers to give me information pertaining their main bearing clearance, rod bearing clearance and rod side clearance.
Here are the tolerances measured at 68°F and also the remark that enlarging the bearing clearances will bring you nothing but LESS hydrodynamic pressure and more oil spraying all over the place!!!!!!

Main b. clear./Rod b. clear./Rod side clear.
Volkswagen .......0009-.0017//.0009-.0017//.008-.016
Volkswag.Diesel..0010-.0020//.0010-.0020//.022-.026
Audi.....................0009-.0017//.0009-.0017//.008-.016
Bentley...............0009-.0017//.0009-.0017//.008-.016
Bugatti................0009-.0017//.0009-.0017//.008-.016
GM.......................0008-.0020//.0013-.0035//.006-.014

All engines except the diesel have their max. Hp at or over 6000 rpm
Volkswagen up to 450 Hp
Volkswagen Diesel 330 Hp
Audi up to 450 Hp
Bentley 560 Hp
Bugatti 1001 Hp

Arnold