Arias P&C 70-723 Info and Piston Slap

[Ronald I. Maciejewski]

I have about 4,000 miles on an Arias #70-723 P&C set and would like to have more information such as alloy and anything else that the forum experts can provide. I know they are 86mm but that's about it.

The set was purchased from Ray Litz at Competition Engineering in 1989 just after the fire at CE and Ray was kind enough to give me a discount along with the promise that they were not heat damaged.

A Norris Cam 337-S was also puRayrchased from CE and the engine was rebuilt with all new bearings, valves, etc. Virtually everything that should be replaced was.

I seem to recall Ray mentioning to expect piston slap and he was right. The slap is noisy and annoying but you get used to it.

So in addition to any Arias 70-723 P&C specifications anyone can provide, I'm interested to know if the piston slap is something to worry about.

Should I expect a short life with this P&C set?

Should I expect a catastrophic event in the foreseeable future?

Should I bite the bullet and replace this set now?

As always, any advice and information is greatly appreciated.

[Ronald I. Maciejewski]

P.S. Sorry for the typo in paragraph 3!

[Martin Benade]

I liked the typo. I would have done it on purpose. My guess is that the slap is merely annoying but not worrisome.

[Craig Richter]

What do you consider "short life"? Sure they slap a bit cold, but you should have many, many miles left. With that cam, rev it up a bit and enjoy!

[Dick Weiss]

When the early B/bore P/Cs came out from C/E, the piston-to-cylinder-clearance was around .008" which is the max. wear limit allowed
by Porsche's 1500/1600 P/Cs. I had one of the 1st 1700 P/C kits and regular driving (not much highway) caused quite a bit of wear after
several 1000 miles which showed up on the sump magnet. The set was replaced w/OEM P/Cs and not problems since.
I've removed a couple Arias B/bore kits due to their lightweight wrist pins shattering! I replaced the pins and have a set or two for sale
after replacing damaged parts. I can bring a set to Hershey for a reduced price to clear some shelf space in my archives.

Dick

[Chuck Allard]

I ran a set of 81 mm Arias pistons in my race car in the late '70s and the instructions said to set the piston skirt to wall clearance at .006 since the pistons would swell after heating up. I had my machinist bore the barrels appropriately. Upon startup, I could hear the piston slap for a while and then it went away. After a season, there was wear on the skirts so I had the pistons knurled to reset the piston to wall clearance. Gave up after that and went with forged pistons with much tighter P to W clearance.

[Craig Richter]

The Arias were the best that was available back in the day. All that clearance was necessary to keep from "sticking" a piston when hot, but too much piston rocking gave rather short ring life. At only 4K miles though, you should still have a lot of life left.
When Dwayne Spencer was developing his forged Shasta pistons, he gave me a set for testing. After a few changes with ring type and pin clips were fixed, that set is still in Speedy's motor and performing perfectly with well over 30K very spirited miles. I think Leonard Turnbaugh sells basically the same pistons today. Much better stuff!

[Neil Bardsley]

It's these two questions that intrigue me.

Should I expect a catastrophic event in the foreseeable future?
Should I bite the bullet and replace this set now?

As a layman do I understand correctly that piston slap accords because of a two large gap between the rings and cylinder walls? A short skirt can also be a cause because the pistons move in the cylinder? However, once the engine warms up and the rings expand the slap goes away. Typically the worst that can happy is that the cylinder walls wear and you have to replace the piston/cylinder set. No rod failures etc.

So therefore as Craig said drive them and enjoy the car you should get much more use out of them?

[Wes Bender]

You're correct Neil, except it's the clearance between the piston and the wall of the cylinder. Not the clearance between the ring and the wall (which should for all intents and purposes be zilch).

If there is clearance (and there's got to be some) a shorter skirt allows the piston to rock a little more.

... and +1 on Craig's comment on the Shasta Design pistons and cylinders.

[Ronald I. Maciejewski]

Thanks to all who responded. The forum is always a learning experience.

Bottom line is I'll keep driving it, hopefully more often than I have in the past.

Thanks again, all.

Ron

[Alan Hall]

One other thing that aggravates piston slap is a non-offset piston pin. Factory pistons (except early pre-a pistons) have an offset piston pin which is why they have two exhaust valve pockets and a mark to indicate direction of the flywheel. The offset piston pin causes the piston to be loaded, by gravity, against the appropriate cylinder wall prior to ignition so the piston isn't driven into the wall by the explosion, thus minimizing piston slap. I suspect the Arias piston do not have an offset-pin (and probably have only a single exhaust valve pocket) and hence are prone to piston slap.

[Ron LaDow]

I suspect the Arias piston do not have an offset-pin (and probably have only a single exhaust valve pocket) and hence are prone to piston slap.

This was the rep on the Shasta pistons, but I got a set and had the cylinders honed to fit, and they are as quiet as the NPRs ever were (pretty sure those had offset pins).
As a hot-rodder, we used Arias at .008" and even in a water-cooled engine, they sounded 'agricultural'.

[Steve Proctor]

Several engines ago, I bought a set of Shasta pistons. The running clearances were specified to be very tight. I sent them with a nice set of OEM cylinders to Ray Litz. He was used to MC and Arias forged pistons that grew a lot when they were hot and did not believe the Shastas could be run so tight, so he machined the clearances really loose compared to the spec. With the centrally located wrist pin, they rocked and rattled. I ran into Duane Spencer at Monterey in 1998 and we compared his engine with tight clearances to mine with the loose. Mine sounded like a threshing machine, his was quiet as could be. Got a different set of cylinders and had them machined to spec. Quiet!!

[Alan Hall]

I could be wrong on the timing, but I think the factory went to the offset pin when they went from the plated aluminum cylinders to the cast iron cylinders. The old plated aluminum cylinders ran with a piston to cylinder clearance of less that .001 inch (as I recall the clearance, new, was .0008 inch), so piston slap was not an issue until they started with the larger clearances with the iron cylinders.

[Ron LaDow]

Several engines ago, I bought a set of Shasta pistons. The running clearances were specified to be very tight. I sent them with a nice set of OEM cylinders to Ray Litz. He was used to MC and Arias forged pistons that grew a lot when they were hot and did not believe the Shastas could be run so tight, so he machined the clearances really loose compared to the spec. [...]

I had a well-used set of 83mm cylinders and both the pistons and the spec sheet in hand. Ted (German Precision) griped that he was going to lose money on the job (which is hard to believe, it was T&M, for pete's sake - Ted and I go back a bit), but he cut them in stages, allowing cooling time in between, and finally honed them to the spec.
As mentioned; no noisier even cold, than NPRs.
BTW, Cosworth stopped providing DFV pistons when we were racing. Phil Reilly arranged for JE blanks (you got to design the dome and have it machined), but they ran (from memory) .003" tighter than the Cosworth parts. Everybody who used them found an immediate gain on the dyno; keeping the rings square to the bore is really worthwhile.
Jon, didn't you do Bill's DFV about then ('97-'98 or so?)