Refreshing my ZZ502 short block.
 

I yanked my motor mostly to retrieve the sockets at the bottom of the bilge and decided to give it a check up. I did a leakdown test, and granted it was cold, but was losing over 50% on three holes. At one point I sucked up some sand to get it hot enough to pop the head gasket at the water passage to fill the intake galley with water but the rings between the cylinders were fine, so I had the heads freshened up at that time. But over the few days while it was apart it did get a little surface rust on #4&6 so I took a scotchbrite and wd40 and scrubbed it out in a cross hatch pattern, but oddly enough those are holding ok.

Im hoping to just run a ball hone and new rings this baby but it doesn’t seem that straight forward on a ZZ502 block. I emailed Speedpro, but do you guys have any suggestions on where to go with this? I didn’t measure the depth of the rings but I read these pistons have unusually shallow grooves, otherwise the usuall 1/16,1/16,3/16 set.

The engine has less than 100 hours total and new pistons/machine work would be a season killer.

I have the zz502 but bought block only the stock Merc pistons use total seal rings part number CR5750

I don't know where you are located, but I could get any machine work done in a matter of a couple weeks. No reason to lose a boating season waiting for something like that.

I' thinking he means financially, btw snap your imco plate is going out in the morning.

Its more of a matter between $400 or $4000. I don’t mind yanking it for a full rebuild a few seasons down the road but it’s not in the cards this year. I live in the SF Bay Area where a machine shop can pay $7500mo in rent, so everything here is near double than most places. I spoke with one shop that has a great reputation for its work and fair (relatively) prices and figured about $2500 for just rings and bearings.

Thanks jd

JE makes a set of 502 pistons that are a couple thousands bigger that are reasonable. I have used a couple sets on stock rebuilds. They work well if you have a little cylinder wear. Light hone and drop them in. There is a very good chance with only 100hrs that you won't need pistons though.

http://www.jepistons.com/Products/281916.aspx

That is about the only good thing about living here in the Midwest. Labor is relatively cheap.

Good to know. Most of the info I’ve found is on the Chevelle sites, and it seems unanimous that these are not honed with a torque plate, and honing with a torque plate to make them perfect hogs them out too wide, so those pistons may be a good last resort.

I bet the ring pack is metric, mine were. I bored and honed with Torque Plates because you have more options with standard ring packs. The metric ring packs are to expensive and bad from the start. Used way to much oil also! My 2 cents:D
Your link above was exactly what I used. You have to have the correct honing or the rings will never seat. Pay a good machine shop to do the job correctly!

I finally got home to double check things, and it already has JE700 pistons. :)


Edit in
It May also be worth mentioning that one reason I yanked the motor was to change out the 110lsa cam for a Crane 731. Even with headers there was moisture in the cylinders that may have washed the rings out from reversion.

Moisture from reversion will not wash down cylinder walls, fuel washes down cylinder walls.

True.

I emailed Total Seal and they recommended #T9190 225 cast iron rings with the second ring being gapless. I measured things out and have .003 clearance, fwiw. N/A

https://www.summitracing.com/parts/tsr-t9190-225

I would’ve expected moly rings, and haven’t heard the OSO brain trust being too impressed with the gapless setup.

Any thoughts on this?

.003 is pretty tight. I would personally rather see .005, but if it was running that way with no piston scuffing, it will do so again. As far as the rings, I have used the gapless rings with no issues. I don't think they help performance, but I don't think they will hurt it either. I would trust the ring manufacturer. They know more about it than anyone.

Thanks, Snap.

I measured the pistons at 4.462 1/2” above the bottom and the bore at 4.465, but I was using the T bars to measure the bore and had a heavy thumb on the calipers, so it could easily be the standard 4.466 bore leaving .004 clearance.

I contacted JE for their recommendation on rings, and they said they supply the pistons to GM but not the rings and to pretty much just piss off.

Is this the correct place for the part number?

Attachment 575248

http://www.jepistons.com/TechCorner/HowToIdentify.aspx

I’ve looked all over it for another number but can’t find one. Would you consider this scuffed?

And the bearings are toast. I pulled the #2 main cap off and it has a groove in it. It did have good oil pressure though with 75# at cold idle. It would drop under 20# at idle after a long run and pop back up to 40ish after a moment.

piston looks fine. looks like the crank is going to need polished though.

Earl Johnson said those bearings were too tight from the factory, so hopefully a good polishing will be enough to clean it up and will also help set the clearances. I finally found the very specific rings for this piston, so I’ll drop the crank off for polishing and perhaps get the block honed with a torque plate. They don’t hone with a torque plate at the factory but clearances appear snug so there *may be enough material there to do so.

A quick platiguage check on #2 main and #1 rod show a snug .002. Should be aiming for about .0025 rod and mains and about .003 on the #5 main, yes? Taking the crank in for a polish/check soon.

sounds like a good plan. should be better than new