I had a 1995 z28 with 110,000 miles. The heads warped and my son removed them, had them resurfaced and reinstalled them at his autoshop class. When we started the car, it had rod knock. I gave him the car for his birthday.

He pulled the engine out and found several spun crank shaft bearings. The crank is badly grooved, but oddly there are no burn marks, no scoring. It is shiny and new looking only with grooves. We have no idea what caused this. The spun bearings were all rod bearings.

He thought maybe the oil pump had failed, took it apart and found it was fine. Not the cause.

The oil pan screen had a lot of long thin metal shavings in it. Compression was fine though. No scoring on the cylinders.

Before he re-did the heads, the oil pressure woldl drop almost to zero when the car warmed up and then come up a bit when the car was under load. We took it to several mechanics including a dealer and they all said it was a bad oil pressure sensor - apparently they were all wrong. It ran that way for over a year.

I told him as part his gift I would help him within reason to pay for parts. I was anticipating a few hundred dollars, but we can come up with more.

Our options seem to be:

Turn the crank and buy oversized bearings. (Will we need to replace the rods?), put it back together and see if it will run.

Buy a used crank and new bearings (and rods?). The crank is $200 - $250 used. We have not priced bearings.

Replace the crank and bearings, rods caps etc. with stock new parts about $700 for parts it seems

Buy a "stroker kit" and install new crank, rods, bearings, pistons, rings, etc. This will convert the engine to a 383. I have read this is not a good upgrade, but if we have to replace the crank anyway, maybe it is a good idea. $900

Buy a used engine about $1500.

Buy a rebuilt engine $2500

Buy a 1994 Corvette LT1 with low miles $3000.

We also found a "rotating block" for $225. One cylinder is scratched. I think we would just transfer the parts we need to our block, but i would still put new bearings in it. .

We want to stay under $1000 if possible, since he is going to engineering school next year and it is expensive, but we do not want to do something stupid.

I have rebuild a couple of 4 cylinder engines and one rotary engine, but that was years ago. He has the knowledge he has gained from HS autotech class (1.5 years). Between us we probably know enough to really mess things up. However he has an experienced mechanic helping him at times (the shop teacher) but he is not an expert in LT1 engines and available options and he is overseeing 30 kids, teaching them and trying to help them with their various projects. He is spread thin.

The car has nostalgic value to us because I bought it just before he was born, so he has been in that car his whole life. We want to make it usable again if practical, but we cannot spend a ton of money.

Suggestions?

Thank you

 

Hard to say what would cause grooves, could have been a piece of bearing that broke and got caught between the two surfaces or just contact from oil starvation.

Before you make any decision take everything to a competent machinist and have him check everything. The crank and rods may be reusable with a slight turn or they may be junk. He may also have a useable rotating assembly he could make you a deal on as many machinists keep parts on hand for that reason. He may also be able to get you a good deal on a replacement.

Personally I wouldn't do a "budget" stroker kit for something like this. You're likely looking at a Scat or Eagle cast crank which are less than desirable pieces. Stick with a factory crank and rods with new bolts.

 

Thank you. We were looking at Scat and Eagle. I guess we will not look at those. We do not want cast. Is there a forged stroker crank that is not insanely expensive?

Fortunately we have a really good machine shop nearby. Their pricing is a bit odd, but it seems cheaper than many other places. Everything they do is in increments of $24. Resurface the heads $24 each, Valve seals $24 to install a set. I forget what all else we have had done, but everything is $24 or $48.

Is there any particular brand to type of bearings we should use?

The groves are the width of the beatings.

Any ideas on what might cause the oil shortage? Oil pump is fine. I did not let it run low on oil and it did not use much except right before we re-did the heads.

There is a rotating assembly on Ebay for $225 or $250 but on cylinder has a scratch in the liner. I do not want to risk that, but is it practical to take the parts out of it and use them in our block?

 

Your engine probably didn't have any oil pressure because the rod bearings were shot. My advice is to have the crank turned and polished and get the oversize bearings. Have the rods resized. Have the bores and pistons checked for the possibility that you could just have it honed then do new rings (tight budget) or bore it larger and get new pistons (which would be my choice at 110k miles). I like the 383 - there is nothing wrong with it. But it is extra cost to you, and you don't really have the budget for the new cam or the head work to make that a good choice (mo money), so I would leave it as a 350 or 353 and save some money for gaskets, oil pump, water pump, head bolts, and distributor if it is needed.. The machine shop will assemble the engine for you for about $350 or so, or your shop instructor should be able to help with the shortblock, since it is similar to a SBC, which he should certainly know how to do.

 

Not really. For what you seem to be planning a stock displacement build with the stock crank should be fine. Figure a good 4340 crank alone will run you $600+.

King or Clevite would be my choice. I have Clevite in my 383 and King in my 408. If you have a few extra bucks I would splurge for the coated bearings but they aren't a necessity. Just a little insurance.

If you check the pick up it's probably clogged with metal shavings along with the insides of the pump and possibly the first inch of the block passage. The shavings from the rod bearings generally get stuck in the screen and cause the pump to cavitate which kills your oil pressure and everything else.

$250 + freight + tear down + machining and that's assuming it's not garbage. Have your machinist inspect your parts before you buy new or used pieces which may require more time and money. If the crank is unusable ask the shop if they have a 1 piece late model SBC crank for sale and go from there.