A new weird problem.

An acquaintance of mine bought a titled partial 850 about 20 years ago, and left it in his barn. The guy who sold it to him was frustrated that he couldn't make it run. Last year, I bought it. I have no time to restore it, but I needed a head and cylinders for another project so I took the engine apart. The head was ugly but fine. It's all restored now. Today I started inspecting the cylinders to see which overbore it needed. To my shock, there is NO taper and it's dead on a standard bore. I got out the pistons to check the skirt clearance when I found the problem. The rings were hard stuck in the slots and the gap was maybe .002" - no way to measure since the rings were all the way in the slots and I didn't get any of the compression rings out in one piece. So, I did some measuring. The top ring in both pistons was .0632" thick and the middle was .0625" thick. A stack of feeler gauges (checked with a micrometer) that was .0630" thick would go 90% into the slots and a stack .0640" would only go halfway into the slot. The pistons are marked AE inside (I think that means original Hepolite), but the rings appear to be Hasting (3-piece oil ring). Even the oil ring was very difficult to get out of the slot!

I'm guessing that the cylinders were changed, the rings were oversized and not properly gapped, but I can't figure why they was no clearance in the slots. I measured the slots of a bunch of old Hepolie pistons and they were consistently Edit: .065 to .066 wide without being cleaned up and the rings that came off them were tight in these pistons. The pistons are marked ID66 on top.

None of this really matters because I will use new pistons and rings, but I'm wondering if someone has an answer.

We call those ring grooves.

With the ring grooves narrowing, I am guessing the pistons were used and the flexing of the rings during travel wore the outer section of the ring lands... if you use a section of the ring, can it rock up and down when in the groove? Wondering what the piston measurements are... worn at the skirts? were the pistons tight in the bores?
For your measurements, you note the rings at, "top ring in both pistons was .0632" thick and the middle was .0625" thick.", and, " I measured the slots of a bunch of old Hepolie pistons and they were consistently .0350 to .0360 wide"... should that be 0.063"?
How are the groove depths compared to the depth of the rings?
I'm thinking you are right with new cylinders and old used worn pistons.
I see the HEPOLITE RING PACK NO: R26730 compression rings are
WIDTH: 1/16" (1.588MM)
RADIAL THICKNESS: .124" (3.140MM)

concours said:

We call those ring grooves.

Click to expand...

Any useful feedback? Yes, I generally call them grooves except when I don't.

Groove: a long, narrow cut or depression, especially one made to guide motion or receive a corresponding ridge.
Slot: a long, narrow aperture or slit in a machine for something to be inserted

YukoNorton said:

With the ring grooves narrowing, I am guessing the pistons were used and the flexing of the rings during travel wore the outer section of the ring lands... if you use a section of the ring, can it rock up and down when in the groove? Wondering what the piston measurements are... worn at the skirts? were the pistons tight in the bores?
For your measurements, you note the rings at, "top ring in both pistons was .0632" thick and the middle was .0625" thick.", and, " I measured the slots of a bunch of old Hepolie pistons and they were consistently .0350 to .0360 wide"... should that be 0.063"?
How are the groove depths compared to the depth of the rings?
I'm thnking you are right with new cylinders and old used worn pistons.

Click to expand...

Yes - typo, edited, thanks.

The problem put more simply: The groove is slightly narrower than the ring which is why they were hard jammed into the grooves.

The piston skirts show no wear, tiny bit of carbon on the tops. The skirt clearance is ~.0035" with the original pistons. A .003 feeler gauge slides in easily, a .004" is a very tight fit. Haven't tried it with new pistons yet.

This is a weird problem that does however have a simple solution.

I know you want to know what happened, but sincerely, in this case, knowing won't improve your next build.

You have an excellent set of donor barrels, look after them, they are expensive to replace.

You have a useless set of pistons, introduce them to the scrap metal bin. Go have a beer!

SteveA said:

This is a weird problem that does however have a simple solution.

I know you want to know what happened, but sincerely, in this case, knowing won't improve your next build.

You have an excellent set of donor barrels, look after them, they are expensive to replace.

You have a useless set of pistons, introduce them to the scrap metal bin. Go have a beer!

Click to expand...

Mostly already done (don't drink) - just interesting (at least to me).

Theyre LANDS actually ! .

Id be rather loath to dispose of O.E.M. pistons . Inspect them under a strong light with a eye glass .

If theyre virtually unmarked - Dont Loose Them .

Sitting for 20 years unlubed , theyre bound to be stuck . Castor Oil'd stick em real good .

Matt Spencer said:

Theyre LANDS actually ! .

Id be rather loath to dispose of O.E.M. pistons . Inspect them under a strong light with a eye glass .

If theyre virtually unmarked - Dont Loose Them .

Sitting for 20 years unlubed , theyre bound to be stuck . Castor Oil'd stick em real good .

Click to expand...

Nope.


The land is only one feature of the ring groove. Thanks for playing though!

That would be a double nope! The land is the area between the grooves!

Here's was AI says about it: "Piston ring lands are the areas of the piston between the piston rings. The overall diameter of the ring land in a common piston is smaller than the overall diameter of the piston, and in many cases, there is a small vertical taper. The reason for this size differential is that once the piston reaches top dead center, it rocks in the bore. If the piston ring land were the same diameter as the skirt, the rings would be required to handle the thrust load. The job of handling thrust loads is best left up to the piston skirt" So, it's got to be true!

Come on, we need more than three to play!

BTW, if I include the normal smiley faces the post doesn't save so...

Hi Greg, I included a smiley face and it seems to work.

another test

This is fixed.