Piston Questions

Veedubber63 · Post by **Veedubber63** » Tue Mar 29, 2005 8:30 pm

I did a search for these questions but couldn't find what I was looking for. First of all, I've got my heads off of my engine which don't know the displacement other than it is a dual relief 1600 dp case and has dp heads. I am wanting to find out what size of pistons they are. I read on here that the size is stamped on the top of the cylinder, My question is where exactly would it be stamped?

My other question, These Pistons look different then any others that I have seen. these are dished and is about the size of a half-dollar in the center. Can anybody tell me anything about them? Are they a special brand or what?

Thanks,

J.W.

VGM · Post by **VGM** » Tue Mar 29, 2005 9:09 pm

The dish is a late stlye factory piston feature designed to lower compression without enlarging the head chamber.You have stock VW pistons most likely.

63ratster · Post by **63ratster** » Tue Mar 29, 2005 11:53 pm

Soak the piston in some carburetor cleaner or maybe even spray some brake cleaner on the top of the piston to remove the carbon and reveal the pistons numbers.

Veedubber63 · Post by **Veedubber63** » Wed Mar 30, 2005 6:17 am

Ok. Thanks Guys. That's the info I was looking for.

J.W.

RoWaMe · Post by **RoWaMe** » Wed Mar 30, 2005 8:27 am

The numbers are very small, like 3/16". Stamped into the top surface of the piston, usually within 3/4" of the edge. They would be in millimeters, so that you'd see something like 85.46. This number is rounded off to 85.5 in tech spec's. I'd agree that you have stock-diameter pistons if they are dished; might've been used for a bus (lower compression = lower heat due to heavier loads). They "could" also be the 83mm pistons for a 1500 engine which would have the numbers 82.9X. If they were the slip-in "87s" then the number would be 86.9X. But 87's were not made "dished".

Post by **Marc** » Wed Mar 30, 2005 9:56 am

The early 1600 Type I engines (`70 and 1971 up to July) used flattop pistons, after that dish-tops were commonplace. It's nearly a universal practice to substitute flattop 311 198 069F pistons when rebuilding a "dishtop" engine, even though the dished pistons are still available under 211 198 069, both because they're cheaper and in an ill-advised effort to increase the power output (it raises the C.R. by about ¼, enough for a barely detectable increase in power but definitely too high for today's Regular gas). Because so few builders use dish-top pistons there's a good chance that these are the original ones from the factory and worn completely out by now. Press the top compression ring into the groove and see how thick of a feeler gauge you can slip in alongside it.

Veedubber63 · Post by **Veedubber63** » Wed Mar 30, 2005 6:32 pm

Ok, I measured the cylinder with a tape measure and it was 3 7/16 which is 3.4375" . I found a calculator through a search that converts inches to millimeters and it says that 3.4375 is 87mm which means I've got a 1641cc. is my math correct? I could get the top of the cylinders clean enough to see any number stamped on pistons, so that is why I measured with the tape measure.

also is there an easy way to tell what size rockers I have?

thanks,

J.W.

turboblue · Post by **turboblue** » Fri Apr 01, 2005 7:19 am

[quote="Veedubber63"]Ok, I measured the cylinder with a tape measure and it was 3 7/16 which is 3.4375" . I found a calculator through a search that converts inches to millimeters and it says that 3.4375 is 87mm which means I've got a 1641cc. is my math correct? I could get the top of the cylinders clean enough to see any number stamped on pistons, so that is why I measured with the tape measure.

also is there an easy way to tell what size rockers I have?

thanks,

J.W.[/quote]

I wouldn't think they are 87's with the dish.
Never have seen a set unless someone had modified them.

Post by **Marc** » Fri Apr 01, 2005 7:53 am

turboblue wrote:...I wouldn't think they are 87's with the dish.
Never have seen a set unless someone had modified them.

Me either, although I suppose it's possible that someone like REPCO may have produced some. There were also factory exchange engines with oversized pistons in rebored cylinders, 86.0 and 86.5mm. A tape measure probably isn't accurate enough to positively identify the difference, which is only 1¼ sixty-fourths of an inch per half-millimeter.
All stock rockers have the adjusting screw at the valve end, most "ratio" rockers have it at the pushrod end. Stock rockers were made in 1.0:1 and 1.1:1 ratios (`65-up); the 1.1s have two parallel raised ridges on their side. There's also a 1.25 rocker made from the same casting as the 1.1 by machining the socket that the pushrod goes into as close as possible to the shaft - to tell a 1.1 from a 1.25, look there - if the socket is roughly centered in the available material they're 1.1, and if it's offset markedly towards the shaft they're 1.25. Odds are you have 1.1s.

dmbfanintn · Post by **dmbfanintn** » Fri Apr 01, 2005 11:21 am

[quote="Veedubber63"]I found a calculator through a search that converts inches to millimeters [/quote]

To convert inches to millimeters, simply multiply your inch value by 25.4.

Just FYI!!

Chris.....

Guest · Post by **Guest** » Sun Apr 03, 2005 9:01 am

Hey, Thanks for the info. I found how to do the conversion after I posted that. also, I still couldn't figure out which rockers I have but I'm going to guess they are just stock.

Thanks,

J.W.