KC John

I had a severe blow-by problem so I pulled my ZZ3 engine apart yesterday and found my problem. The lands on 4 cylinders were broken all on the same bank (1,3,5 and 7) Thankfully there is no damage to the cylinder walls. I'm pretty sure this was caused by detonation, but I don't know why it only affected one bank. The broken pieces as well as the piston itself are rounded over as though this has been happening for a while.

Not sure what to do at this point. Can the bearings be reused? Should I align bore, hone, leave the crank alone and just fix the pistons. Not sure what to do. The engine probably only has 25k-30k on it, but doing too much to bring it back might cost more than a new crate motor. I do see a few marks on the bearings, but I don't know enough to determine if they should or could be used again. The only reason I would use them again is so I know everything is exactly like it was without any geometry problems.

What do you feel is the minimum I can do to this engine and not regret it? This motor will eventually have a centrifugal blower on it with only 4-5 lbs. of boost. I'd like to put forged pistons back on these rods and put it back together with a new set of heads to lower the compression ratio. This is being done mostly for looks and an occasional rip for fun.

Here are some pics and a short video.





Video for a better look:



Are these hot spots or damage to the bearing itself. I'm certainly a novice when it comes to the inside of an engine.


This is the back side of the bearing and rod, does this look normal?
They have scratches that make them look like they have spun, although I know that can't happen.

jimh_1962

Well thats not good! How does the crank look?

I would tear it down and replace all of the bearings.

Replace the one piston maybe check the rest and make sure you did not damage anything else. Replace the piston rings. Get the crank polished probably...

You already have it torn down enough to finish the job. New gaskets and put it all back together. Not sure what was done before with the engine has over bored???? Make sure the cylinder walls are good to go. Then again does not answer why it happened...

Randy G.

What does the top of the piston look like? The rod half of the rod bearing looks like it's been taking a beating. If it turns out it was caused by detonation I would spend the money to replace all the pistons because there may be breaks or cracks you can't see. I would also have the crank checked, and everything measured by someone who knows how to do it (cylinders, mains, pins, both ends of the rods, etc.). Detonation is hard on everything.



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427Hotrod

Yes...you've got good 'ole fashioned detonation damage. When that happens the upper rod bearing shell and the lower main bearings get hammered. I can't tell if the tangs are still on the rod shells, but if they are it didn't spin.

Since this is destined to be supercharged:

I'd tear it all the way down. All that metal bounced around in there. If the main bearings look OK...might not need to have line honed...but I'd have it checked. Ck rods for out of round after the abuse...easy for machine shop to ck and correct...but don't spend a fortune on them. Aftermarket rods are often cheaper than fixing stockers if you upgrade bolts etc. Definitely go with forged pistons. Hypereutectics like you have will do that again. I'd have cylinders bored and honed with a torque plate since I was buying new pistons anyway and it's got some miles on it. You "might" be able to torque plate hone them round and keep std bore...but I doubt it.

Of course now you may be down to new pistons and rods...how much more for a crank to make a 383???

JIM

GTOguy

I concur with the above posts. Bearings/pistons have severe detonation damage, and it needs a thorough going over, blower or not. And the cause of the detonation needs to be determined to avoid an encore performance...........

KC John

I guess I'll need to get some prices from a machine shop. I plan on going with forged pistons anyway, but like I said with machine shop prices so high I might just go with a crate engine.

I find it hard to believe that having all but pistons, rings, bearings and gaskets could cost as much as a crate, but I guess I'll find out soon enough.

domenic tallarita

I agree with all and there is another SLIM possibility that the pistons are off set and were installed backwards on that bank. I found engines with off set pistons pressed on some rods by the re builder.

Dom

427Hotrod

Remember...the average crate is just like you have. Cheap parts put together cheaply. Works fine for low HP stuff...but if you want to make power and have it live....you're going to need better parts and better machine work.


JIM

69ttop502

I would listen to Jim on this one. When I had my engine built, the shop had a crate motor from a well known source there with very low miles on it. It was a mess. Told me he gets them all the time. Good machine work is the key on these things. Never know what you have with a crate and the warranties are useless. Now you will know exactly what you have when rebuilt.

karkrafter

Cast hypereutectic aluminum pistons, better than old cast pistons but still really light duty, blower...FORGED pistons.

Use better fuel and knock the timing back a bit.

KC John

The pistons are sooty, but they don't look like they have any damage.

colo63sw

Years ago some buddies and I helped a fellow forum member with a new crate motor; it had lousy compression right out of the box, big piston to bore clearances. It was a mess.

cv67

another vote for Jim....To many crates with name brand stuff but crappy machining what good is that.
May as well work with what you have, x3 on thos bearings getting hammered bad good thing you took it apart when you did.

427425

Jim is absolutely correct about crate engines. A good daily driver at best, if you don't lean on it, too much. I agree with everyones assessment of detonation. The back of the bearings appear to have had some moisture on between the bearing shell and the rod. Most likely condensation. The #1 piston has something going on...the lower piston top has either kissed the head, or oil/water has removed the carbon from this area on the piston. I would remove the head gasket from the block and make sure you do not have a crack from a head bolt hole into the edge of the cylinder. If the block is ok, I would consider a rotating assembly with better crank, rods and pistons. The labor is going to be basically the same for machine work and rebuild. This way you know what you have and can be more assured that the engine can withstand your plan for boost.
I have blueprinted and balanced many of the dirt track crate engines, and many, many NHRA/IHRA stocker engines, and they are all far from stock factory parts. No one that races the crate motor classes run these motors as purchased. I hope this helps with your decision.

Westlotorn

Certainly detonated to death. Since the damage is limited to one bank I suspect you had a vacuum leak on that side leaning it out. Study the underside of your piston heads.
Lean burn will leave a temperature mark on the piston under the piston head.
Gold color shows they were really hot, black shows they were even hotter. Study all eight and see what you learn.
I understand there are some good crate builders out there but I fully agree a lot of them are way less than high quality even direct from GM and Ford.
I trust word of mouth supported local shops.

Westlotorn

I looked at your pictures once again tonight. I can tell you the cylinder finish is less than good.
Your second piston rings are a tapered face ring. At 35,000 miles the taper should be about 20% of the ring face. Yours are about 60-70% worn. This is shown by the face being silver, the part not yet worn is still black. A good cyl finish will show less wear on the second ring which allows the second ring to scrape oil better and gives better oil control. Good cyl finish lets the rings work better. Used rings tell a lot.

cardo0

Ya know if you are really trying to do a budget blower motor if it were me I would look for a good used block. The late '70s L82's and early 80s L83's had forged entire assemblies and low compression heads with large chambers that flow pretty darn good for stock iron heads.

I did a C3 forum parts search using justL82 engine and found at '77 L82 17k mi motor right at the top. Didn't even have to try for a a L83! You should install q better cam for a blower though.

Hope this can help and maybe save you $$$$ for a more serious effort with all costly machine work.

John BX NY

GM geniune parts engines come with a 3 year, 100k mile warranty. Performance engines come with a 2 yr, 50k warranty.
It's getting hard to justify rebuilding that 350 that's been under the workbench for years. The shops that did a lot of machine work back in the day are long gone in these parts.

vetteman64

I love the smell of blow by, in moderation. My wife thinks I am crazy and hates the smell. Won't find it in most anything on the road made after the 1980's.
C Ya, Joseph Rock
Frankenstein 59

69ttop502

But check the terms of those warranties. Not a great deal when you consider the pain of removing the engine and hauling it here and there and all the hassle involved. I would still rather deal with someone local and get known, high quality machine work. My GM crate that was in my car when I bought it left a lot to be desired.