Can these pistons be salvaged?

by Sleddogg Sat Sep 01, 2012 10:51 pm

Good evening,

A few days back I picked up Pontiac 400. The seller had the rocker covers and the valley pan cover off for inspection...everything that I could see was super clean. I could tell that at some time in it's life, it received either a rebuild or gasket set as aftermarket gaskets were everywhere. The seller did not have much info on the motor...he got it along with about 38 other engines in some sort of buy-out of a body shop a number of years ago (as a side note, I have NEVER seen so many big block chevy motors in one place, this guy as a TON of 396's) but he did offer my money back if it wasn't rebuild able, So, took it home and pulled the heads and noticed that a portion of the cylinder head on #1 had small little divots in head, not on the valves or the "dome"...but above where the valves sit. The picture will explain it better than I can. There were also about 20 small dents, divots, impact marks.....on the piston itself in the corresponding area. #1 has about 20, #7 has about 12, and #4 has a few as well, with #1 being the worst. They are very small...some have thread impressions and they are not very deep. Obviously something foreign entered this motor, but, I suspect, it happened at startup with just the starter turning the motor or it was shut down immediately when whoever noticed something amiss, as the damage is not nearly as bad as it could have been and the pistons are not completely chewed. The cylinders are perfect...not a scratch anywhere...no gouges nothing. I haven't pulled the pistons out yet to see if the ring lands are compressed...but wondering if this is something anyone else has any experience with? I don't mind buying new pistons..but could these be salvaged or is it end of the road for these guys?

Thanks gang,

Jesse

[img] Can these pistons be salvaged? Piston10

[/img]

[img] Can these pistons be salvaged? Head110

[/img]

by ant7377 Sat Sep 01, 2012 11:42 pm

Ive never seen that before. It kinda looks like some kind of damage from detonation. Maybe pull it out and take it to a machine shop.

by Sleddogg Sat Sep 01, 2012 11:57 pm

That was my first thought as well, that it was detonation damage. But on one of the pistons you can actually see small indentations of threads...kind of like a grub screw...but I know that a screw wouldn't travel from cylinder to cylinder and if it did, seems to me it would damage the bore as well. These are clean bores...very slight lip, but no damage at all. Weird.

by Sleddogg Sun Sep 02, 2012 12:01 am

Oh and my suspicion of rebuild was confirmed. These are .030 over Speed Pro forged aluminum pieces according to the part number stamped on them. This is the only thing amiss with this motor everything else is beautiful..bearings, cam, lifters, crank, rods all look real clean...even has new rod bolts. Can't vouch for the rings yet, but this is very strange scenario.

by BlackChevelleSS Sun Sep 02, 2012 3:05 am

yes a screw or any other object can travel from cylinder to cylinder. It can hang valves open too.....Dont ask how I know

by Joe73 Sun Sep 02, 2012 9:00 am

Lots of questions with that block. Rotate the assembly and look at the cylinder walls. if theres a good "nick" in one of them your looking at another bore job. Your 30 over already. If the walls look good then I'd bring the block, rods and crank to the machine shop. Let him check it out. You may luck out with no bent rods or crank. Then you would be talking a set of pistons and you should be good. With some luck.
Or if you find a good nick bring it back to the guy and show him. Tell him the shop says its not rebuildable and get your money back.

by 1973 454 MONTE Sun Sep 02, 2012 9:32 am

Back in 86 i needed a motor for my 75 monte. I bought one from a trusted yard. Got it home, cleaned it up and put it in. Hooked it up turned the key and and here a tink tink kinda sound. All of a sudden BANG.
There was a one inch piece of screwdriver shoved through the spark plug tip and out the threads into the head. Needless to say i took it back and got money back.

by Sleddogg Sun Sep 02, 2012 2:13 pm

Definitely gonna take it down and have it looked at...probably Tuesday. Joe73, I have found no nicks, gouges or anything in the cylinder walls...they really are in good shape. I am gonna have the machine shop have the final say on this one Smile

Thanks

by BlackChevelleSS Sun Sep 02, 2012 2:35 pm

Id sand the top of the pistons down a little and run it, wouldnt hurt anything. I had a valve guide come apart on my 454 with 1000 miles on it, Piston looked worse than yours, ran 12.39 @111mph before it came apart on street tires. Now has about 5000 miles on it and I ran 12.42 @113 mph last month.

by jerry46765 Sun Sep 02, 2012 6:12 pm

If you have some deadline to meet, put it back together.

If not, a replacement piston is $50.
Why not replace it while you have it apart?

Thanks -

by Joe73 Sun Sep 02, 2012 6:34 pm

I like that idea. Let the machine shop have the final say on the block. But I'd also let them check the rods in case one is bent from trying to compress and unknown object in there. Better safe than sorry.

by pila Sun Sep 02, 2012 8:34 pm

I've repaired a few marine engines, which were Chrysler 360 types, that had piston nicks from screws etc that fell into the carb/intake. The nicks in those pictures are minor. It takes a fairly large/hard object to damage the edge of a piston enough the cave in the top ring groove, and that piston and head looks like superficial damage to me. If it were me, I would pull that piston, inspect it, and like you did , inspect the cylinder wall. New rings might be a good idea, depending on wear etc. And if bearings etc look good, run it, after lubing the cam & lifters with break-in/assembly lube.

by Sleddogg Sun Sep 02, 2012 10:18 pm

I finished tearing it down this evening. All the piston rings looked great with the exception of #4. That piston had the least amount of "screw marks" or whatever it was...however the top ring was completely stuck in the groove near one of the impact sites.

So, to answer my own question, I am not salvaging these slugs...it's going to the machine shop on Tuesday..hopefully it doesn't need any boring...it's already .030 over. I am crossing my fingers for just a hone. The crank and rods were standard sized. The crank hasn't even been turned...bearings were sweet too,but it's already apart and I am gonna just do it right. I will probably spring for new rods too. There really is no deadline on this engine other than my own self-imposed one Smile

My 350 is still in the car and just need to button up a few things and it should run for a while until this 400 is good.

I will let you guys know what the machine shop says about all of this craziness.

Take care,

Jesse

by pila Mon Sep 03, 2012 8:06 pm

Forged pistons aren't cheap. Maybe the machine shop can give you an opinion on them.
If you aren't going to hammer on this engine, the KB hypereutectic pistons would be fine. Don't know why you mentioned rods...but they can be checked also. I haven't ever used forged pistons, and I beat the hell out of my engines. Full race is a different game of course...

by Sleddogg Tue Sep 04, 2012 12:27 am

Thanks for the feedback guys. I meant to say that I might spring for new rods...i typed that I probably would, I didn't notice that until now. It all depends on what the shop says. Gonna carry the whole mess down tomorrow to the shop, hopefully they can give me some good news. Here is a few more pics.

This is one of they cylinders...can't remember which, I think #4. Pictures of cylinder bores are kinda sketchy...they are smooth, but awfully shiny.

[img] Can these pistons be salvaged? Bore10

[/img]

This is the #7, this is not a flat spot on the side of the piston..it is an illusion of the camera. It is a real clean spot, and this is the point that the ring is trapped. Will not move or expand. The ring wasn't broken but I am sure compression on this cylinder was garbage.

[img] Can these pistons be salvaged? Piston11

[/img]

Again, thanks for all the feedback! I really do appreciate it.

Thanks,

Jesse

by pila Tue Sep 04, 2012 1:46 am

The cylinder walls indicate quite a few miles, as well as the scuffing of the piston in the picture. Maybe not unusual for a forged piston (?) Any ridge at the top of the bores ?

by Sleddogg Tue Sep 04, 2012 11:18 am

There is a bit of a ridge...enough to catch a fingernail on. Some of it is carbon build up, but enough of it is metal to be noticeable.

by dragons_lair59 Tue Sep 04, 2012 7:34 pm

should be able to hone it out then but machine shop would tell ya for sure

by pila Wed Sep 05, 2012 1:09 am

You can always go to .040" over on the bore too, with new pistons. I had to do that on my 400 SBC because a broken ring left a score in the bore. That's only a .010 cut on the bore, beyond the .030. which still leaves good thickness in the cylinder walls, and ends up at 408 Cu IN. .040 pistons are not common, but Summit had them.

by Sleddogg Wed Sep 05, 2012 1:50 am

Today I took the block, crank and rods down to the shop (heads are another story for another time Smile

).

I have been dealing with this shop for a couple years on some other projects (non engine related) and trust that he does good work and respect his opinion. He mic'ed the bores and said that they were within specification to live with a hone, and the crankshaft was still standard. He recommended a hone on the cylinders and polishing the crank. I showed him the pistons and he honestly wasn't that impressed with the damage. We talked about what this motor was gonna be used for (basic driver, some showin' off, maybe a trip or 5 to the track a year). He recommended that I knock off the high spots of the hits, and run 'em. He said that those pistons are plenty strong and as longs as there are no cracks after cleaning, dress them up a bit and run with them. I expressed my concerns with possibly a bent rod on those pistons, he said that he will check them, but he doesn't think the impact was enough to damage them. I will check them to be safe. So, I guess I take a chance and run the pistons....maybe a few years down the road, when I (hopefully) will be working again, I can revisit the pistons and replace...but I think I am just gonna run em.
I did consider a .040 overbore on this gig, but I think I might save the pennies at the moment. Thanks for all the help!

Thanks for all the feedback

Jesse

by 1973 454 MONTE Fri Sep 21, 2012 4:55 pm

1973 454 MONTE wrote:Back in 86 i needed a motor for my 75 monte. I bought one from a trusted yard. Got it home, cleaned it up and put it in. Hooked it up turned the key and and here a tink tink kinda sound. All of a sudden BANG.
There was a one inch piece of screwdriver shoved through the spark plug tip and out the threads into the head. Needless to say i took it back and got money back.

and here it is......lol
Can these pistons be salvaged? Img_1010

by 77mali Fri Sep 21, 2012 8:39 pm

Holy F****** Turd

^^^^^^^^^^^

How much to polish the crank & clean the components? And engine build can get expensive fast. Your plan sounds good- hopefully nothing is bent or cracked but the place your talking to sounds trustworthy from your post. Good luck.

by Sleddogg Fri Jan 25, 2013 3:22 am

Hey guys,

Bringing up an old thread, but wanted to apologize for just dropping off the face of the earth Smile

Amazing how babies can monopolize your time Smile

Update on the 400, it's done and back running in the car...runs good and strong. I was able to re-use those pistons, after a lot of cleaning and love. So, the GP is running around again. Next project is running some new exhaust and (Much) later, swapping out some higher compression heads.

Take care!

Jesse

by 77mali Fri Jan 25, 2013 8:06 am

Congrats on the baby & also the motor!

by Biomedtech Mon May 06, 2013 10:33 pm

1973 454 MONTE wrote:
1973 454 MONTE wrote:Back in 86 i needed a motor for my 75 monte. I bought one from a trusted yard. Got it home, cleaned it up and put it in. Hooked it up turned the key and and here a tink tink kinda sound. All of a sudden BANG.
There was a one inch piece of screwdriver shoved through the spark plug tip and out the threads into the head. Needless to say i took it back and got money back.

and here it is......lol

LOL That'll teach someone to put motorcrap parts in a chevy motor! Glad you got your money back!

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