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Tech / General EngineIs your car making a strange sound or won't start? Thinking of adding power with a new combination? Need other technical information or engine specific advice? Don't see another board for your problem? Post it here!
Hi. This is my first post ok thirdgen.org
i bought a 1986 camaro last year, 305 and t5 transmission
I have bought a 1970 4bolt 350 that im going to build for the car. Today i was taking off the pistons and crank to change cam bearings and inspect main and rod bearings.
Long story short. When i was inspecting one of the rod bearings i fumbled and dropped it. The piston hit the floor and cracked a bit of the skirt off
I Want to just replace the one piston since i already have spent a lot off mony on the car and engine. I dont think i can afford going for a set of new forged rods and Pistons.
The number inside the piston is 3892673. Do anybody know what piston will have the same specs as the OEM? The block isn't bored up and the cylinders look ok. Going to hone them since im already there. I assume the standard size is what to go for. Oversized will probably create some issues i believe
There’s a set of used ones on eBay, pretty sure there 6cc pistons.
might be worth getting a set of silv o light or similar if your compression and quinch works out to run those pistons.
That piston was already destroyed before that happened. Look at the scoured-away place on the top ring land, right above the broken-off piece of the top ring. Looks like detonation from crappy fuel, causing that damage right below the spark plug from the explosions. That cyl wall is probably also damaged, meaning that cyl needs to be bored, meaning the other 7 will as well.
If that's any indication of the overall condition of this engine, you need a full set of pistons and rings, after some machine work. Otherwise you'll have what we affectionately refer to as a "Krylon rebuild"... a fresh coat of paint slathered onto on a worthless oil-burning smoking short-lived pile of used-up worn-out GARBAGE parts.
Show us the rest of the pistons, and the #6 cyl wall on the side toward the outside of the block, and maybe we can help you judge whether that's the case.
Note that this doesn't necessarily require a new set of rods; unless those also turn out to be damaged somehow. Other than the factory's unbelievably crappy "quality control" (wherein they NEVER let their "quality" rise to a level that might be considered "out of control"), which may equally turn out to be true of the block, rods generally don't "wear out", as such.
The engine was taken out from the 70 camaro because it startet to run poorly. One of the cam lobes was worn down. (I still have the old cam) Why they sold the engine is not known to me. I bought it from another person that bought it from the guy that owned the 70 camaro. Reason to why he who i bought it from sold it was because he had a car that was not legal to change according to the state
(in Norway its called "verneverdig". It is when someone registers a veteran car as it. It is possible to get it registered as a normal car again but it is a whole process)
Getting the cylinders bored is not possible around here. If im going to do that i need to borrow a pickup and find someone that can do it for me. Not so easy. I can take more pictures tomorrow
Forgot so write this. Im going to use heads from a 88 Corvette. (113 heads) they have 58cc so the compression is going to go up a bit. 10.8:1 i believe with flat top with 4 valve release pistons
Since i most likely can't get just the one piston i was wondering if the summit brand pistons is usable for my build. Link under
It's too bad that you don't have a salvage yard near by and your could go grab a piston for a few bucks. Getting one piston around here would be a piece of cake.
I don't see why those Summit pistons wouldn't work. They will work. I don't know that you'll have a "100,000 mile motor" on you hands w/a hone job and pistons, but it'll work pretty good for a while.
Might consider something like this instead https://www.ebay.com/itm/35305167920...mis&media=COPY
how far are the pistons in the block ? What cam are you using?
hard to recommend parts of your just slapping it together and expecting the best. Btw have you selected a flywheel yet ?
I have a luk standard flywheel for pre 86. I want to use pistons that are the same design as the OEM. (flat top with 4 valve releases) as long as the compression wont get to high. I see rock auto sell silv-o-lite flat top with 4 valve release. Are they any better then summit. Looks similar
OK, so we know it has at least ONE of the well-known 70s "quality control" problems; The Lifter Bore Problem. That's the situation wherein the lifter bores weren't machined properly at the factory, such that the lifters aren't properly aligned to the cam, which makes it EAT that (those) cam lobe(s) and lifter(s). Seems to be concentrated mostly at the pass side rear of the blocks that have it; cyls 6 & 8; although sometimes it affects others. But, usually toward the rear of the block.
That's why it was sold.
Lesson #1 in buying used old classic car parts that "should be" EXTREMELY valuable: if the price seems affordable, the part is JUNK, and the seller KNOWS IT. All he wants is, to get rid of it, for as much money as possible.
Getting the cyls bored is not a problem ANYWHERE in the 1st world. People do it all the time to Sabb, M-B, BMW, Citroen, whatever. It's all the same. Engines ALL wear out in the same ways (or get destroyed, like yours did) and need to be renewed. Only thing that's different among ANY of them is, the bore diameter. You don't need a "specialist" to do that, except if you're building something "high performance", in which case you'll want for the final steps to be performed by someone with a "torque plate" that they can bolt down onto the block to simulate the distortions that bolting up actual heads will cause.
Show us the cyl walls, especially #6 where that destroyed piston and ring were located, immediately under the spark plug.
Hopefully the block doesn't have any of the other "quality control" problems that plagued GM engines back in those days. I'm not going to type them up again; see this thread from earlier just this week https://www.thirdgen.org/forums/tech...r-general.html see post #2 where I described them in some detail. I used to build LOTS of motors back in the 80s; mostly for lower-level (hobby) race cars, but LOTS of street ones as well. I can't begin to tell you how anguished my customers were when it turned out that some "romantic" and "desirable" block they had somehow miraculously "run across", turned out to have one of these (or other) Problems. Now, you already know your block has one of them, The Lifter Bore Problem; you don't know yet how many OTHERS it also has. To put it in perspective, about 1/3 of all 70s motors were born with The Starter Bolt Hole Problem, because evidently GM had 3 machines that drilled those, and ONE of them was EFFFED, and drilled the starter bolt holes in the wrong place.
I really hate to rain on your parade, but I'm seriously thinking, you got RIPPED OFF when the thief sold you that motor. It's not anywhere near useable as-is, and there's a VERY good chance that no matter how big $$$$$$ you spend on it, it will NEVER be useable. It's just The. Way. It. Is. I hope not, but be forewarned. "Hope" is a notoriously ineffective business plan. Metal doesn't respond to it.
Good points, I’ve seen a lot of posts online with failed lifters wiping cams by not using zinc additives. Hopefully the block isn’t junk. That would suck to wipe another cam and ruin it. Makes me wonder about excessive wear on crank .
Looks like the piston hit the concrete on the headland and the rod swing broke the skirt. Looking at the wear on the rest of the piston side I'd suggest a new complete set. If the bore doesn't have much of a ridge at the top you could get a basic set of cast pistons, get the ridge cut and cylinders honed and run it. I'd guess the cam wear might be normal for a high mileage motor. I have a 400SB tore down with much better looking pistons and the cam in that motor was worn too (and the plastic timing gear was really shot.)
I can feel some of the marks with my fingernail. I assume i need to get it bored up and then need a new set of pistons and rings. Might as well pay the price to get it right. Rather that than to hope for the best and possibly grenade on a roadtrip
I plan on keeping the car more than just a couple of years so i don't want to rebuild a engine every winter. I need to hear around if it is a local place to get it bored. I know of a guy through work that machine's heads. Maybe he also can bore the block
But what are your suggestions on the compression. The heads already have upgraded springs and retainers so retainer to guide clearance is within. Heads was used with a zz4 cam and a procharger in the L98. The cam lobe that was worn down was intake on cyl 1
But if 10.8:1 is to high what pistons should i go for then?
The darker part i can feel with my fingernail
Last edited by Norway-kent; Feb 4, 2024 at 07:11 AM.
OK, so we know it has at least ONE of the well-known 70s "quality control" problems; The Lifter Bore Problem. That's the situation wherein the lifter bores weren't machined properly at the factory, such that the lifters aren't properly aligned to the cam, which makes it EAT that (those) cam lobe(s) and lifter(s). Seems to be concentrated mostly at the pass side rear of the blocks that have it; cyls 6 & 8; although sometimes it affects others. But, usually toward the rear of the block........
Hi Norway-kent,
With all due respect to your enthusiasm toward getting this project done & over with, it appears in your response that you skipped over the most important part of Sofa's post, and have gone right back to worrying about pistons. Were this mine, and had I just learned of a possible problem with the block casting itself, I'd think my FIRST order of business would be to learn how to determine if the block has the lifter problem or not. If you don't have a viable block, it really don't matter what pistons you buy, now does it?
Long time since i have been on this thread now since i lost my interest on sharing here.
The engine build is done and was installed in june. I got the block bored so its now a 355cid. New hypereutectic pistons and polished crank. I have driven it over 1000miles without any problems. A whole lot different to drive now from when it was a slow 305
Good looking rebuild and good to have had it rebored. Did you go with the GM heads? And I'd say it really does outperform that 305! Take it easy on that T5 gearbox though. You into Corvettes too?
Yes i went for the 113 gm heads. They are actually from the corvette in the background. Its my brothers project. He is putting in a LM7 with a big cam. Hopefully it will be ready for the next season
Cool to see old American cars in Norway.
I was there a couple of times long ago and enjoyed seeing them driving around like it was normal.
When I was there I was in Honefoss and Oslo mostly.
We did drive all the way up to Molde to visit my then girlfriends family.
Good times.
