Parts Catalog Accessories Catalog Tech Info Tech Forums
 
  Search our site:    
 Cart  | Project List | Order Status | Help    
Go Back   Pelican Parts Technical BBS > 1- Porsche Technical Forums > 911 Engine Rebuilding Forum

Reply
 
LinkBack Thread Tools Rate Thread
Author
Thread Post New Thread    Reply
up-fixing der car(ma)
 
YTNUKLR's Avatar
 
Join Date: Aug 2002
Location: Fremont, CA
Posts: 3,508
Garage
Send a message via AIM to YTNUKLR
Deck Height Issues......

Took the weekend off of school to head home to Socal to finish a client's 2.8 short stroke motor.

Here are the specs. so you guys know what's up-
'77 930/02 case
2.2 crank, knife-edged, 2.2 rods (66mm stroke)
JE custom pistons, dome vol. ~48.7cc
3.2 95mm cylinders
modified 911SC heads. With twin plugs, volume=90cc (spec. for stock, single plug)
DC80 cams

I checked the deck height (using solder), got around 1.6mm with NO cylinder base gasket. Checked it again because I couldn't believe it. Yep, 1.6mm. Checked with a .25mm gasket and it goes up, as expected, to about 1.85mm. This is way too high. Not even mentioning its increased propensity to detonate, the compression falls from 10.65:1 to about 9.8-9.9:1. Dammit.

I really do not know why this is. The case spigot surfaces are perfect and the case has never been decked before. The only real possibilities are 1) the rods were resized improperly by Ollie's, or 2) JE made the pistons just a tad off.

So, now I see I have two options: 1) call JE and futz around with getting new pistons (?) or 2) machine the cylinders down at the spigot seat (not the head face) by .035" or so. Also I would machine the chain boxes the same amount.

Any input? Henry Schmidt?



Thanks for any help,
Scott
__________________
Scott Kinder
kindersport @ gmail.com
1970 911E coupé albertblau - projekt

Last edited by YTNUKLR; 02-25-2007 at 01:36 PM..
Old 02-25-2007, 01:32 PM
  Recommend this thread for the PelicanWiki    Reply With Quote #1 (permalink)
Moderator
 
304065's Avatar
 
Join Date: Dec 2001
Posts: 9,290
Scott, I know you realize that what you are measuring with the solder is NOT the deck height, but the piston-to-cylinder-head clearance. If there is a flat lip at the edge of the piston it is posisble to measure from there to the cylinder top with a depth micrometer or the end of a vernier caliper (not the jaw end). But Wayne's book, and the CE technique he cites, both claim a range of 1.25 to 1.55mm.

OK, so what is the EXACT cylinder height? What is the height group marked on the side and then, using a caliper or a height gauge, what is the height of the one you show? The spec for 2.2/2.4/2.7/3.0 Turbo (hereinafter, the "62mm Engines") is 85.400-85.425mm for Height Group 5 and 85.425-85.450mm for Height Group 6. Admittedly, there's only .025mm of tolerance if you were expecting the shortest and got the longest but you need to be certain and it's an easy measurement.

Next: What is the compression height of the JE piston? Measured between the flat part at the edge and the top of the pin boss, then add 1/2 the pin diameter. Compression height should not be different than it is for all the 62mm Engines. This is not a measurement in the spec books, but JE certainly knows what it is.

You didn't check the rods after you got them back from Ollies, but you can still pull one off and verify a 130mm center-to-center distance. The procedure is to measure the distance between the inside edge of the big end and the inside edge of the small end, then measure both small and big end inside diameters and add back half of each measurement. You will have to replace the bolts and nuts and carefully retorque but it beats a complete teardown.

I agree with you that if the case had been decked you would probably have the opposite problem, as the pistons would be sticking too far out of the hole.

I'm guessing that the pistons are out of spec only because everything else is a "factory" part and you would probably have to really try to offset bore the rods by half a mil.

But of course I am FAR from an expert so I defer absolutely to the genuine ones who are probably watching the Academy Awards at this moment. Once they get disgusted, perhaps they will chime in . . . so expect more answers in about ten minutes
__________________
'66 911 #304065 Irischgruen
Ex-'71 911 PCA C-Stock Club Racer #806 (Sold 5/15/13)
Ex-'88 Carrera (Sold 3/29/02)
Ex-'91 Carrera 2 Cabriolet (Sold 8/20/04)

Last edited by 304065; 02-25-2007 at 05:27 PM..
Old 02-25-2007, 05:23 PM
  Recommend this thread for the PelicanWiki    Reply With Quote #2 (permalink)
Registered User
 
Join Date: Oct 2001
Location: Momence, IL 60954
Posts: 1,820
Send a message via AIM to cnavarro
I was thinking the same thing as John, what is the exact cylinder height... they may have been a little tall, taller than what was used to set the compression height and hence the effective deck on your JE's.

If you do decide to shorten the cylinders, say by machining the deck that seals against the case, the real difficulty is without the proper tooling you'll end up with probably .0005-.001" variation in head to deck length of the cylinder measuring at say 45, 135, 225 and 315 degrees, meaning the bore won't be perpendicular to the deck anymore and there is also a chance that the cylinder tops won't be parallel to the cylinder bases.

It sure would be easier to blame it on JE or the rods though! Just check them out and ask more questions. Your going in the right direction.
__________________
Charles Navarro, LN Engineering
http://www.LNengineering.com
Aircooled Precision Performance

'99 Boxster powered by Flat 6 Innovations; '10 Cayman S (DFI testbed)

Last edited by cnavarro; 02-25-2007 at 06:36 PM..
Old 02-25-2007, 06:32 PM
  Recommend this thread for the PelicanWiki    Reply With Quote #3 (permalink)
up-fixing der car(ma)
 
YTNUKLR's Avatar
 
Join Date: Aug 2002
Location: Fremont, CA
Posts: 3,508
Garage
Send a message via AIM to YTNUKLR
The cylinder is a height group 5, it was resurfaced (a couple thou of an inch) on the top (Ollie's). Now=just under 85.4mm, so we're in business here, if not just a tad short! Took off a rod, also and it measured 130mm center-to-center. The cylinder and the rod are confirmed fine.

I want to compare my piston order spec. sheet with some others I have and see if there is anything off with this particular set, will do when I get back to school.

John, I've talked to a lot of builders that recommend keeping it right around 1mm if possible. That is factory spec, any looser and I think you are giving away compression, hp and increasing the likelihood of detonation.

Charles, your fears are my fears. Seems like it would be hard to get a perfectly parallel cut at this critical junction..

Will keep you guys posted with additional info

boo

Scott
__________________
Scott Kinder
kindersport @ gmail.com
1970 911E coupé albertblau - projekt

Last edited by YTNUKLR; 02-25-2007 at 08:53 PM..
Old 02-25-2007, 08:45 PM
  Recommend this thread for the PelicanWiki    Reply With Quote #4 (permalink)
Moderator
 
304065's Avatar
 
Join Date: Dec 2001
Posts: 9,290
Scott, of course you are right about 1mm deck height. That's what I plan to use in my own rebuild. I mention the other figures insofar as they are Walt's which are referenced by Wayne in his book.

Is there any damage to the cylinder spigot that would keep the jug from seating all the way? What is the OD of the cylinder at the bottom? What is the ID of the spigot?
__________________
'66 911 #304065 Irischgruen
Ex-'71 911 PCA C-Stock Club Racer #806 (Sold 5/15/13)
Ex-'88 Carrera (Sold 3/29/02)
Ex-'91 Carrera 2 Cabriolet (Sold 8/20/04)
Old 02-26-2007, 07:47 AM
  Recommend this thread for the PelicanWiki    Reply With Quote #5 (permalink)
up-fixing der car(ma)
 
YTNUKLR's Avatar
 
Join Date: Aug 2002
Location: Fremont, CA
Posts: 3,508
Garage
Send a message via AIM to YTNUKLR
John, no damage. The case is perfect.

ID of the spigot I believe is 103mm, I'm not sure of this (top of my head). The OD of the cylinder? Didn't measure it but it's the same as any 3.0/3.2/3.3/3.4. These are stock 3.2 carrera cylinders (unmodifed except for the moons), and stock case, spigots are stock. There should be nothing weird about it...
__________________
Scott Kinder
kindersport @ gmail.com
1970 911E coupé albertblau - projekt
Old 02-26-2007, 11:49 AM
  Recommend this thread for the PelicanWiki    Reply With Quote #6 (permalink)
Registered User
 
Join Date: Oct 2001
Location: Momence, IL 60954
Posts: 1,820
Send a message via AIM to cnavarro
Hmm, even more interesting. Where did the JE's come from?
__________________
Charles Navarro, LN Engineering
http://www.LNengineering.com
Aircooled Precision Performance

'99 Boxster powered by Flat 6 Innovations; '10 Cayman S (DFI testbed)
Old 02-26-2007, 11:56 AM
  Recommend this thread for the PelicanWiki    Reply With Quote #7 (permalink)
Try not, Do or Do not
 
Henry Schmidt's Avatar
 
Join Date: Apr 2004
Location: Fallbrook, Ca. 92028
Posts: 5,288
Sounds like a 3.0 95 mm piston with 3.2 95mm pin location.
The .030" difference you are dealing with is easily explained by this manufacturing error.
Custom pistons are generally built to the engine builders specs. Where did JE get the specs for these pistons?
__________________
Henry Schmidt
SUPERTEC PERFORMANCE
Ph: 760-728-3062
Email: supertec1@earthlink.net
Old 02-26-2007, 08:47 PM
  Recommend this thread for the PelicanWiki    Reply With Quote #8 (permalink)
Registered User
 
Join Date: Jan 2004
Location: CT
Posts: 8,070
Hey Scott

For what it's worth.....

I faced this same problem when building my RSR spec motor for my clone. I could not get consistent readings using the solder method.

I ended using the depth gage feature on my digital calipers to measure the distance from the seal surface on the cylinder to the lip along the circumference on the pistons. I used a dial gage to ensure I had TDC and measured at 4 different locations along the circumference of the piston. I was able to repeat within +/- 0.1mm using this method and got deck ht data that made much more sense than the solder method.

Good luck and I'll be following your thread.
__________________
Tom Butler
1973 RSR Clone
Old 03-03-2007, 06:09 AM
  Recommend this thread for the PelicanWiki    Reply With Quote #9 (permalink)
Moderator
 
304065's Avatar
 
Join Date: Dec 2001
Posts: 9,290
Hmm, Henry makes an excellent point.

If you look at JE's web site the "compression distance" is listed as follows

3,0 95mm x 70.4 -- compression distance 34mm
3,2 95mm x 74.4 -- compression distance 32.8mm

So there is a difference of 1.2mm between the two off-the-shelf pistons JE offers in 95mm size. 1.2 mm = .047" for those using the decimal-inch system (It won the War, didn't it?)

So. . . you can backsolve into spigot height for a Porsche engine. . .

74.4 stroke divided by two equals 37.2, plus 127.0mm rod length, plus a compression distance of 32.8mm =197mm "TDC Height."

197mm TDC height PLUS 1.0mm for deck height minus 85.4mm for the cylinder height minus another .25mm for the spacer leaves you with 112.35mm for the distance between the seat face of the spigot and the centerline of the crank.

Plug those numbers back into a standard 2,0 engine for fun. . . half of 66 is 33 plus 130.0 rod length plus 34mm compression distance = 197mm TDC height.

Ahh, fun with numbers! Once I get my case on the surface plate with a height gauge I will confirm the spigot height.

Anyway, Scott, back to your problem. What was it again? Just kidding.

If you plug a compression distance of 32.8mm into the above calculations. . . 33 + 130 + 32.8 you end up with 195.8mm TDC height. In order to get that back you would have to deepen the spigot bore, lengthen the rod, offset bore the pin, shorten the spacer, trim the cylinder or have new pistons made. Of those, the easiest is probably offset boring of the rod, which would alter the rod-to-stroke ratio to an even 2:1, not necessarily a bad thing.

edited to ADD the deck height to TDC height before subtracting the cylinder and spacer to get the spigot height.

edited: 2,0 and 2,2 cylinder height is 82.2 mm-- so the spigot height must be different on those engines.
__________________
'66 911 #304065 Irischgruen
Ex-'71 911 PCA C-Stock Club Racer #806 (Sold 5/15/13)
Ex-'88 Carrera (Sold 3/29/02)
Ex-'91 Carrera 2 Cabriolet (Sold 8/20/04)

Last edited by 304065; 05-29-2007 at 10:32 AM..
Old 03-12-2007, 12:21 PM
  Recommend this thread for the PelicanWiki    Reply With Quote #10 (permalink)
up-fixing der car(ma)
 
YTNUKLR's Avatar
 
Join Date: Aug 2002
Location: Fremont, CA
Posts: 3,508
Garage
Send a message via AIM to YTNUKLR
John, you are correct.

The pistons must have just been made with the 3.2L wristpin center location in mind, but for a 22mm wristpin (not a 23mm like you'd get on a 3.2L), as that would account for the deficiency. Machining the cylinders sufficiently is not really feasible and machining the case is untenable (would require significant disassembly for no good reason).

The worst outcome of this is that I will pull off all the rods, and rebush them 1mm longer. I don't have my spec books with me (school) but I think 2.0 rods are 130.0mm stock. Just a minor correction, but the rod/stroke ratio would be 1.985:1 after lengthening them to 131mm. A tiny bit more piston dwell near TDC doesn't hurt.

Thanks for all the ideas everyone

Scott
__________________
Scott Kinder
kindersport @ gmail.com
1970 911E coupé albertblau - projekt
Old 03-14-2007, 02:40 PM
  Recommend this thread for the PelicanWiki    Reply With Quote #11 (permalink)
Moderator
 
304065's Avatar
 
Join Date: Dec 2001
Posts: 9,290
Lemme see. . . 33+131+ 32.8= 196.8 TDC height

112.35 + .25 + 85.4 = 198 to top of cylinder

Leaving you with a 1.2mm deck height for 10,39:1 compression. I think this is in the acceptable range, could be slightly less depending on the exact cylinder height.
__________________
'66 911 #304065 Irischgruen
Ex-'71 911 PCA C-Stock Club Racer #806 (Sold 5/15/13)
Ex-'88 Carrera (Sold 3/29/02)
Ex-'91 Carrera 2 Cabriolet (Sold 8/20/04)
Old 03-14-2007, 03:40 PM
  Recommend this thread for the PelicanWiki    Reply With Quote #12 (permalink)
 
Now Available for Ordering:   101 Projects For Your BMW 3 Series 1982-2000  [more info]
Old 03-14-2007, 03:40 PM
Reply

Thread Tools
Rate This Thread
Rate This Thread:

 



All times are GMT -8. The time now is 04:19 PM.


 
Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2011 Pelican Parts - Posts may be archived for display on the Pelican Parts Website -    DMCA Registered Agent Contact Page
 

DTO Garage Plus vBulletin Plugins by Drive Thru Online, Inc.