Piston trademark ID?

[Steve Hatfield]

Can anyone positively identify this piston dome marking by factory/source and define the numerical code adjacent to the three vertical lines? And finally, does the number code define angle of squish, 22 or 30 degrees?
Thanks in advance.

[John Brooks]

Paul

I don't have my book in front of me, but that looks like a size mark. The Pistons were measured and the are several versions of the same bore. If I remember right there is 5 sizes, they vary about 0.0005 larger as the marks go up. It's in the spec book and the service manual.

Are they all the same?

[Ron LaDow]

Steve,
The answer to your question will have to come from someone far above my pay grade, but- BUT -*BUT*!!!!
If that is a shot of a piston dome in a running engine, I really want to know WIH you are doing. I don't think I've seen a dome that clean after, say, half-hour break-in run on a dyno.

[Steve Hatfield]

Thanks guys.
John, (I’m Steve not Paul) all four pistons are with the same and all four are stamped 82.94.

Ron, I picked this engine up recently from a fellow registry member who in turn got it from another member several years ago but never ran it.

So before I tear into it I was doing s little NDIA. It appears that the first owner (as documented in the Maestro’s data base) performed some restorative procedures before he buttoned it up and let it go on to the member I from whom I acquired.

All four pots appear to be as new with what I think are first over vintage Mahles and never before run!
The engine, marked as a Normal from ‘63 has some interesting aspects:
- 360 degrees pulley
- steel homemade blanking plate over the fuel pump port
- alloy rocker stands
- very small end float
- lathered in MMO
- Narrow exhaust ports (indicating 22 deg heads)
- S-90 ball vented rocket covers
- entire engine very clean but not show clean as in walnut or soda blasted..,more like race-cleaned
- stamped 010 comp B under the oil cooler (which I’m told indicates line bore by Walt)

I performed leak down with all four at 10% loss (cold, very cold engine)

More to follow...

[Neil Bardsley]

excuse my ignorance but what is

"360 degrees pulley" (Is that a pulley with no holes?)
ndia
mmo
WIH

???

[C J Murray]

We have a couple of guys posting here that use some unusual abbreviations thinking we know what they mean. We don't. I will guess...

mmo= Marvil Mystry Oil

360 pulley= marked in degrees all the way around

[C J Murray]

WIH="what in hell" (maybe?)

ndia= (wants to spellcheck to India but I doubt that is correct)

[Steve Hatfield]

Two outa three - not bad CJ
Non-Destructive Inveatigative Analysis

Sorry, I’ll try to be more expressive in the future

What about my question re piston markings?

[Dick Weiss]

Steve,

I looked at a set of 82,93/82,95 pistons and found no such mark on them; Yours look like it's the letter M for Mahle. But a circle #?
Are the cylinders cast iron, full aluminum, S90 Ferrals w/fully machined fins, or Birals w/cast-on aluminum fins?
Make a 22 and/or 30 degree template to verify the piston crown--same for checking the head chamber(s).

Dick

[Steve Hatfield]

Hi Dick,
I mis quoted the size. They are 82.94. The cylinders are cast iron.
The M like stamp also has 3 above the M and the number 116 beneath the M figure.

I have since pulled one head owing to nearly zero compression after rechecking the valve clearances.
So definitely 22 deg heads and pistons but with a heavily worn bore. Maybe needs just rings after measuring all. the heads looking very nice, once I inspect/overhaul the valves, I’ll probably be in the market for a set of Leonard’s 22 deg/86mm p’s and c’s or maybe AAs.
Haven’t decided if I’ll pull it down all the way but I’m very curious to witness the results of the alleged line bore by Walt Watson at Competition.

I’ll report.

[Dick Weiss]

OK Steve,

Your pistons are in between the + 1 & -1 dimensions listed in the spec book.
Heavily worn cylinders? Do they have the usual wear (+ .003-.006") @ the top 1/4" caused by the top ring reversal in heat?
They won't hone out for the cylinder to be straight & round which will increase the clearance to the piston skirts and "rocking pistons" won't allow the rings to seal properly plus having larger gaps.

The real necessities are the equal heights of the cylinders to be w/in .001" (better w/in and equally w/the cylinder-seat depths and
NOT exceeding .385" deep; A 22 degree chamber angle can be flycut to 30 degrees but it'll be limited by the edge of the exhaust valve seat-ring. Also the chamber edge diameter should be near the diameter of the cylinder bore as best as possible and checking the chamber cc's after new or refinished valves are installed; Hopefully, they'll be equal w/a cc or 2.

Dick

[Ron LaDow]

[...] Also the chamber edge diameter should be near the diameter of the cylinder bore as best as possible [...]
Dick

Dick is correct; this is key to avoiding detonation and piston failure.
(AFAIK)It is nearly impossible to measure the edge of the conical chamber cut match the cylinder bore closer than +/- .01". But if you ignore the issue or miss by .08" or so, you cannot build a successful engine with a C/R even as low as the factory numbers; it will rattle on opening the throttle at low RPM (with a street cam).
Matching those dims as closely as possible, and doing careful C/R volume measurements allows 9.5:1 in a single-plug 616 on pump gas, with a short ignition lead.
Miss those dims and the measurements badly enough and 8:1 will rattle on the best pump gas you can find and shortly fail a ring land.

[Alan Hall]

If the pistons are truly "new" 82.94mm, you can get a set of used, worn 82.5 cylinders at very low cost and have them machined to the correct bore to match the pistons...but not sure how or why anyone would have put an engine together with new oversize pistons and well used oversize cylinders, doesn't make much sense.

[Steve Hatfield]

Thanks Alan; good idea.
Based on earlier comments, I’d prefer to keep the bore to a minimum.
This engine is full of surprises.
The push rods are very light alloys. No wear on the alloy stand-type rockers.
Peering into the right side after removing numbers 1 and 2 pistons I’ve discovered a 102 S/S90/912 cam (in this Normal stamped case) in near perfect polished condition (all the way round), no wear whatsoever on the oil pump tang or cam slot and a polished cheeks non-counterweighted crank marked 010 R; Std M. in sharpie pen on the number 2 cheek. Rods are all polished later 912 style with evidence of lightening at the bottoms of the big ends.
Next step, I’ll carefully measure piston skirts to verify wear status and usability considering your suggestion. Then the heads...

Looks like maybe a race-prepped engine with clapped out jugs.