Topic: Head/Piston ID

[JLeather]

I'm picking up another former turbo-engine for parts and I've got a couple questions for the board gurus.  First off, is this an F or K head and does it look stock to you?
 
http://img200.imageshack.us/img200/9997/head6b.jpg
http://img23.imageshack.us/img23/9240/head2lou.jpg
http://img198.imageshack.us/img198/4154/head3.jpg
 
It looks like an F combustion chamber, but it looks like K valve keepers.  Do you have a professional opinion?

The really weird one is the pistons that were in the engine.  Here's a shot of them still in the jugs, and then 2 closeups:

http://i86.photobucket.com/albums/k113/JLeatherman_CF/Bikes/pistons.jpg
http://img4.imageshack.us/img4/7779/piston1.jpg
http://img23.imageshack.us/img23/4494/piston2m.jpg

Now, I've never seen a picture of them before, but I figure these have to be the MTC forged low-compression pistons that came with the competition version of the ATP turbo kit.  They're supposed to be around 8:1 with a stock K-head.  They are certainly flat-tops, but what's throwing me off is the size of the valve relief.  It might be a flat-top, but with a different compression height so it's still a high-compression piston.  Care to weigh-in on it anyone?

[MRieck]

The head is F2 with what appear to be aftermarket valves with the early keeper system. The pistons are obviously low CR pieces.....I wonder if the skirt could be longer . What do you find this stuff John
  You know what....I'm going to change my mind on the valve keeper set up. They certainly look like F2/3 valves.....I'd say the have the late style keeper groove too. Measure the valve diameters and pop a retainer off....you'll know than exactly what it is. The valve reliefs on the pistons are "properly" cut for the F2/3

[754]

They look like MTCs. Why do you think they are high compression?, the valve reliefs have nothing to do with the compression, in fact they may have made them deeper than need be, just to lower compression.

[JLeather]

754, I'm hoping they're not high-compression.  I've just never seen a pic of the MTC turbo-pistons before so I wanna make sure that there isn't a way these could be flat-top and still high-compression (like changing the compression height for instance).  I haven't seen any other 836 pistons that were flat-top (completely flat) so I'm hopeful these are the turbo pistons I've been in search of.

[MRieck]

Those pistons are certainly not high compression with the F2/3 chamber.... that is for damn sure.

[754]

Get us the pin to deck height measurement, & grab a spare set of 736s to bore to fit them..

[MRieck]

754, I'm hoping they're not high-compression.  I've just never seen a pic of the MTC turbo-pistons before so I wanna make sure that there isn't a way these could be flat-top and still high-compression (like changing the compression height for instance).  I haven't seen any other 836 pistons that were flat-top (completely flat) so I'm hopeful these are the turbo pistons I've been in search of.

I BELIEVE THOSE ARE TURBO PISTONS

[JLeather]

The measurement from the top of the wrist-pin bore to the deck is just a hair under 16mm.  Comes in at almost eactly .625".  Anyone got a stock piston they can lay hands on and measure?  The batteries in my calipers are dead.

[754]

Just measured a 970 Arais with a tape,
 .625 or just over.. BUT dome raises 4 mm or more above deck surface.

So a total of.625 + about.180.. gives aroud .800

[Jerry Rxman Griffin aka MuthaF'er]

My 75 750F piston pretty much has the full crown on the dome unlike the other version that has the crown in the middle. Make sense? The best measurement I could get from the top of the wrist pin bore to the beginning of the crown, keeping in mind the limited length of the caliper arms do not reach to the top of the crown with the wrist pin stuck in place, is .727". I could only insert my caliper as far as the wrist pin which is still in the piston. OR measuring with wrist pin in place, inserting caliper into the wrist pin as far as it will fit, including the thickness of the wrist pin to almost center of piston crown, I get .860"/22.4mm

[754]

Measured a few with calipers, comments added to som.. top of pin bore to outer edge of deck height.

Stock...650 -.660... measured 2 pistons

Yosh 812....625...... didnt even remember having that one..

836cc ...570.. this is a modded 350 2win slug, only part of why they are not ideal!

836cc forged Arais ....640

970cc forged MTC.....600

1080cc cast....610......I suspect this may be Powroll?

..................................................................................

So tell us if the turbo piston has anything cut out of the dome, below the deck height... i think they may have got most out of the valve pockets... BUT ONLY if they are thick enough. would not hurt to check them..

[JLeather]

That's interesting that the stock pistons are .650 and these are .625.  I guess they really should come in around 8:1 like they claimed.  Well see.  Once I get them into an engine so I can check deck and everything I should be able to cc the valve pockets and calculate the definite SCR.

Thanks for the measurements 754.  I'm surprised there is so much variance among the aftermarket pistons.

[MRieck]

Nobody is talking about the size of the chamber and its impact on the final CR

[Jerry Rxman Griffin aka MuthaF'er]

Wise old guru, we are listening.

[JLeather]

Mike, obviously that'll make a difference.  I was just trying to figure them out as compared to a Wiseco or a stock piston.  With that F-head on that engine it was probably more like 7:1 or less.  I don't have them in my hands yet.  The pics/measurements are courtesy of the guy who's selling them to me.  Once I get 'em here and can cc the valve reliefs I can do a real compression calc and see what I've got to work with.  The important thing is that they're somewhere around stock as a starting point.

[MRieck]

 I'm not trying to be a BB John... (though I'm pretty good at it). Those old turbo pistons were all flat top pieces.