96 TA

I hear that for the LT1 the most common problem of internal issues are spun bearings. What causes this to happen and how could one avoid it. Is there a certain weight of oil to use?

Another thing to, I heard a person is most likely to spin a bearing after a cam swap, why is this? What happens as a result of driving around with a spun bearing?

Thanks.

1racerdude

Metal to metal contact will cause it and also the rod deforming with to many RPM's after a cam change.
Ya don't want to go with the TRICK of the week 0/20 oil either,don't care who made it or where it's made.
If ya got high mileage the a 20/40 or 50 should do. I would also consult the OWNERS MANUAL for oil spects.

The results is a BIG hole in the block and it no run so good at all.

96 TA

So is there a way to avoid it?

I know using the correct oil is possibly one way, from your post is sounds like proper break in after a cam swap is another.

1racerdude

On a stock bottom end there are some that have no trouble and others that don't make it a week. Now that's not with a rebuild but an engine with 50-60-70,000 miles on it. I think it is the quality of bearings put in different runs of engines from the factory.
There is really no way to stop it except rebuild and build it for it's intended use.

Joe B

Most ALL of the guys that Iv'e seen spin bearings in their stock bottom end LT1's have been twisting them "OVER" 6500-6600 RPM's where their chosen cams make the most power being shifted........(not that It dosn't ever happen)but I personally haven't seen anyone spin a bearing below that RPM range......so my answer to this concern(while my other bottom end is going together SLOWLY) was to stay a little smaller on cam, so that I could shift between a max of 6300-6400RPM's without giving up much power(especially average horsepower)......no problems so far...........Joe

96 TA

Thanks for the info guys,

Is it possible to spin the bearing WHILE installing a cam?

The Engineer

The actual cause of LT1 rod bearings spinning is due to "weak" factory rod bolts. Under heavy load and high RPM, the rod bolts stretch a few thousands and the rod bearings spin. The powder metal factory rods are great, just the rod bolts are the problem. If you install ARP rod bolts in the factory bottom end, you should be able to prevent spinning a bearing. And, low mileage bottom ends are not excluded from this problem.

http://www.cardomain.com/ride/2189634

shoebox

Wouldn't everyone running high RPMs spin a bearing if that was the case? It might be a part of it, but I don't think it is a cure-all.

The Engineer

Not everyone that smokes (I don't) ends-up with lung cancer, and not everyone that doesn't smoke is cancer free. All you can do is manage the variables that you can control and hope for the best. I believe I said, "the ARP bolts should prevent spun bearings." The word "should" is not absolute.

Most of the machine shops I've worked with around OKC agree the weak factory LT1 rod bolts are the problem.

1racerdude

Weak rod bolts = rod end distortion and it is with the metal too. Not ALL LT1's have powder rods. I have seen pressed powder rods break too from to many RPM's. In fact I have a LS1 here from a customer that has a BIG window in the block from a broken rod from too many RPM's.

shoebox

Lol, then the rod bolts are the problem. Oh, well.

Variables were mentioned. There are more than just rod bolts.

Oiling seems to be an issue as a lot of people lose bearings at the front of the engine (albeit, they are probably higher mileage engines).

Dave88LX

I have a video somewhere.

String

I had a similar problem with the rod bolts. Instead of spinning the bearing, the bolt broke, and then took out the rod, and 2 pistons. I was turning about 6000 rpm at the time on an autocross course. Interestingly enough, the broken parts went through the pan and saved the block. I still have it, but went with a new short block from Scoggin Dickey. So, 6 weeks and $10 grand later, I have a new 383 running to 6600 and pushing 420 at the wheels.

96 TA

Thanks for the info guys, ill look in to getting better rod bolts and bearings in the near future on my 355 rebuild. In the mean time ill hold from spinning the engine past 4500rpm and use some good quality oil.

Dave88LX

Don't waste your money on better rod bolts. By the time you buy new rod bolts, pay someone to press out the old ones, install the new ones, and then resize the big rod end, you could have bought a nice aftermarket set of rods...no biggie since you're going 355, so you'll be getting pistons/balance anyways.