68 327 Piston and ring question

[Happy_dan]

Doesn't seem to be much activity in the engine forum, so I thought I would post a link here. This is about reusing pistons with new rings.

http://www.67-72chevytrucks.com/vboa...d.php?t=815691

[Steeveedee]

If you don't have a bad ring ridge or too much cylinder taper, you can hone the cylinders and put new rings on the old pistons. It isn't ideal, but it works.

[Happy_dan]

There is very little to no ridge and very little taper. As I mentioned, I measured all 8 bores in 3 places and both front to back and side to side. Not much differences.
I am not looking to be really cheap, but cost is always an issue. On the other hand, I don't want to do all this work and skip something that I really should do.

I just want a reliable driver. Not racing, towing or anything extreme. I will measure all bores again after I hone them.

[kwmech]

I've done it before a couple of times without any problems

[hamjet]

At minimum I would rent or borrow a ridge reamer,( about $50.00 new), break the cylinders with hone stones, and use cast iron rings which will seat and break in faster than moly rings. I used to do that in my younger years. (any kind of ridge can possibly break your new top rings.)

[Happy_dan]

Thanks for all the advice. I will continue to work on it.

[special-K]

It's called an overhaul vs a rebuild. Not uncommon and many miles can be had out of a proper overhaul. If they sizes are within tolerance...

I also recommend cast iron rings vs moly for better wear-in.

[Happy_dan]

Absolutely, the plan is cast iron rings for sure.
I will take all measurement. I have already measured all bores and will measure them again after honing just to deglaze. It seems all cylinders are worn slightly more on the bottom as expected but none seem crazy. I can post all those numbers if anyone cares. I used a telescoping bore gauge and a digital caliper. May not be the most accurate as the bore gauge ends cannot sit flat on a round surface, but it's consistent.

[i82much]

I did this with a fairly high dollar aftermarket block Pontiac engine. Had some issues with the first build, lost a lifter at 1500 miles and the rod bearings looked bad. Took it to a new shop and they were able to reuse the pistons without issue.

Of course, the engine only had 1500 miles on it, but I think the fact that the engine builder was willing to do this with an engine with forged crank, rods, and pistons, roller cam, ported aluminum heads, aftermarket block, etc. tells you that it is a legitimate procedure if the measurements are ok. I am pretty sure we went back with moly rings but can see why iron makes sense for your situation, more wear presumably.

[Happy_dan]

I think the idea of iron rings is the bore is not exactly round so they are softer and break into the slight taper or oblong shape better.

[i82much]

Originally Posted by Happy_dan

I think the idea of iron rings is the bore is not exactly round so they are softer and break into the slight taper or oblong shape better.

i have an old 396 in my 72 K10. Will follow this thread with interest to see if it works out, I can definitely see myself trying this out on the 396 if the measurements indicate it is ok. It leaks pretty bad and has a consistent tick in the vacuum gauge, but has great oil pressure and runs pretty well. Seems like a good candidate for an overhaul instead of a rebuild as described here.

[Happy_dan]

I will be sure to update as I move forward. Will take a while as heads and crank are at machine shop and I have been buying some of the tools I need as I can.

[i82much]

this is why it’s a hobby, right? probably more fun to do this than just buy a crate engine. and if you screw it up, it’s not the end of the world! you havea couple of other options in your sig to get you back and forth to work ...

[Happy_dan]

Exactly. I have put less than 1K miles on it since I got it and hopefully I can use it much more often this coming year. It is a nice day only, run around for errands truck! The body and frame are in amazing condition and I really just want it to be close to like it was in 1968.

No drive to work anymore! Forced to work from home and looks like it will remain that way. I have to get a battery tender for my daily! LOL.

The ZL1 is for trips and that is the one I put the miles on. Wouldn't want to think about taking that all apart!

The 68 is simple and doable and time in the garage in the winter here is more like therapy than something that I HAVE to get done.

I have nothing against a crate engine except this truck has so much originality, I would like to keep it that way if at all possible.

[i82much]

Sounds like a fun project. Looking forward to hearing how it turns out.

[Carl Spangler]

Originally Posted by Happy_dan

Doesn't seem to be much activity in the engine forum, so I thought I would post a link here. This is about reusing pistons with new rings.

http://www.67-72chevytrucks.com/vboa...d.php?t=815691

I heartily applaud you for trying to keep the parts as original as possible. The old pistons will likely be fine to “reuse”.

You might also investigate the nearly lost art of piston knurling.

[Happy_dan]

I have started to read about piston knurling. Interesting. I can't tell you all how much it means to have the expertise on this board to help and old man learn some new tricks.

[72c20customcamper]

Used to do this a lot in my youth. Figured it it lasted 20k I was ahead , last one I did something like this was on my daughter's Ford escort she dropped a valve seat wiped out a piston and head . I had a parts car so I took the head and piston from it and put it in hers.Car ran great and she put 25k on it and sold it to a friend who had it for a couple more years.

I didnt even change the rings just used the old ones. This was the era of Mazda engines in fords

[BigBird05]

Since you have the ability to measure the cylinders, then mic the piston skirts to make sure none of them have collapsed. Also check the ring groove to see that they are still square. If not they can be squared up by you, and a ring spacer can be installed along with the new rings to bring the new oversized ring groove back into spec.

[57taskforce]

Good advice here, I would also make sure the wrist pin bores In the piston and rod are still in spec. Mic the big end of the rod also and make sure it hasn’t spun a bearing at some point. Would suck to get it back together and have a knock. I’ve reused pistons lots of times before with good results.

[Happy_dan]

I will check all those things! Thank you for the input!

[incoma]

I worked in a machine shop for a year or two. We reused pistons regularly. No problem. Key is to get your cast rings to seat properly on startup and breakin. Definitely use a good hone for this. I’d be curious how much clearance you have from piston to cylinder wall. We would hone in a clearance of .003 -.005. If i recall I think you can buy slightly oversized rings too, but I may be thinking of something else.
Posted via Mobile Device

[Happy_dan]

Just a quick update. I bought a ridge reamer and knocked the ridge down and honed the cylinders. I need to measure all bores again and I see some scratches in the walls of some cylinders. I may just just send it to machine shop and have it bored .30 over and get new pistons but I have a mechanic friend that will take a look for me and advise. In the meantime, heard from machine shop on heads. Some valves had been replaced and have oversized stems. Some seats need replacing. I am going to have them replace odd sized valves, replace bad seats and all exhaust valve seats. They are also working on the crankshaft. I’ll update as I go. Probably not until after holidays.

[BigBird05]

My 2 cents worth is, with all of the work you are doing and low cost of .030 over pistons for a small block Chevy, you should go ahead and bore it oversized. I would be a shame to go thru all of that work and have it use oil.

[Happy_dan]

Your two cents is worth a lot to me!! I am definitely leaning that way and a cam and bearings too. Thanks so much for all the replies. Typical project!!