Hey y'all, I've got a 1985 Trans Am WS6 and I'm not anticipating the day I get a new engine, as opposed to the current 305. I found one on Facebook, it's a 355, 2 bolt, comes complete, yet in parts with one piston pulled, as it was "bad" according to the owner. He said the motor ran but then lost power and he said all it would need was a new piston (and assuming rings too?). I'm 16 and not a guru when it comes to motors, but financial reasons forced me to learn as much as I can about these engines. I really like the idea of a 350 bored .30 over and yet the piston looks kinda rough. It's a hypereuretic piston, p/n sum-17350-30. He sent pictures of the bad piston which I will post here.


I am assuming this is ring failure? Any reasons why this wouldn't happen again?



Inner ring looks messed up



This looks like maybe mechanical damage, this is what scares me



Ugly chip visible


Also he was asking $200 but said he could let go of it for $150. I'm not sure if this means it wasn't worth the hassle for him or if it's a waste.

 

Pass. You can find a good 350 for $500.

 

Looks like someone used NOS with low octane pump gas or did a really crappy slap together rebuild. What's it worth? I wouldn't give more than $100 just for the core value.

As mentioned above, find another engine. No sense spending money on an unknown engine which will need a lot more money. You're basically going to be buying a core which will need a complete rebuild.

Technically, it can be a whole lot cheaper to buy a prebuilt crate street replacement engine from some engine builder. It might seem like a lot more at first but there's a lot of small things you can never account for plus the prebuilt engine will normally also have a warranty.

 

The only reason I'm considering this is its maybe a couple hundred for new gaskets, and not too much for new piston and rings, then put it together. It's hoping to work on this long term and tinker with it for the next 6 months-year, maybe try to learn to port and polish the heads, swap the cam, cause everything is already apart for a freshening up. Anywho, I'm gonna sleep on it before I do anything dumb.

 

Their is no cheap fix for that motor. If you pay $200 for it you will have more into it than a running $400-500 motor.

 

so, obviously the piston and rings are shot. But most likely the head, the intake, the valvetrain, the carb and maybe a couple other things are fine. This motor is already bored .030 over and I could get it for 150. It's 13 bucks for a new piston from summit racing. Is the block still good? clearly that piston is gacked but he said the only the ring and piston was bad. Is there any reason why I should steer clear? I'm not trying to be stubborn but I just want to understand why y'all recommend that I stay away. Would the block need to be bored out? He said nothing about the bores being bad, I know you can go .040 and .060 over but I figured I could keep the block, heads, intake, and carb and whatnot. Thanks for the advice.

 

Buying a new piston is easy. Is the bore sized properly for it to fit, probably not. Slapping an engine together like that may work but don't expect it to last long. There's a big difference between assembling an engine and building an engine.

You also have no guarantee the block is any good. I threw out a $3000 Dart block and bought another because it got a crack in the casting above the mains from a couple of engine failures.

If you buy that engine, it would be more economical to buy 8 new larger pistons and have the block bored out again providing there's no cylinder wall damage from the bad piston/ring. Cost of new pistons, cost of machine shop work etc, etc all adds up. Eventually, you'll be up to or over the cost of a new replacement engine. Don't kid yourself. Building an engine properly isn't easy or cheap.

As already said, buy a running engine and drop it in.

 

This. Hes showing you the piston but whats the rest of it look like, and where did that chunk go? I dont even know if i would pay $100 for it. Summit brand parts scare me - Its all made in china stuff.

 

Not all 350 blocks can take a .040 over bore. I had one that sonic checked too thin for .040 over.

Get a running engine to work with not one that's already grenades. I would have zero confidence in using that motor unless it was torn apart and rebuilt if that's possible in this case.

 

Since I know realise you're actually trying to learn I'd like to explain a little more to you.

You should never replace just one piston; perhaps if you had an identical brand/style piston and it was very similar in weight it would work fine but chances of that aren't too good. Next, if you replace all 8 that's good but you'd need to pay to have the crank/rods/pistons rebalanced.

I suppose you could slap a new piston in that motor and try your luck but I don't think the end result would be anything good.

 

Okay, thank you very much. The pistons that are in it are the same as the one I was looking at. I do not think I will be going with this motor after reading all of the bits and pieces that'll need to be throughly checked. A couple guys near me have 350 blocks, some bare, some just a bottom end. It'll probably make sense for me to throw some 906 heads on a shortblock rather than dump money that I don't have into this. Theoretically, if you had the exact same piston from the same manufacturer, would it work?

 

If you are looking to "build" a motor but have no mechanical experience, I'd suggest you buy a running $500 350. Start with the basics, intake manifold, headers, full exhaust, etc.

Building a motor (even just freshening up the motor and stabbing a cam in it) will cost much more than you think. Don't forget to factor in all the tools you probably do not have at this point (torque wrench, valve spring compressor, ring filer, and all your tools to check tolerances; although on a low revving performance motor, plastigage will probably be fine).


Nobody is trying to take you out of building a motor but we want you to know what you are going to invest into this. Even just buying a running motor and putting a cam in it will cost you about a grand.