Pelican Parts
Parts Catalog Accessories Catalog How To Articles Tech Forums
Call Pelican Parts at 888-280-7799
Shopping Cart Cart | Project List | Order Status | Help



Go Back   Pelican Parts Forums > Porsche Forums > 911 Engine Rebuilding Forum


Reply
 
LinkBack Thread Tools Rate Thread
Author
Thread Post New Thread    Reply
Registered
 
Join Date: May 2005
Location: Cambridge, Ontario (Ayr)
Posts: 288
Max Moritz - Machining Valve Pockets

My 3.2SS rebuild from a '79SC is progressing. I have mocked up the engine to do the piston to valve clearance.

The pistons are 98mm Mahle Max Moritz and the cams are DC20. My deck height is about 1.1mm, the heads have been chamfered. The heads are off my '79SC. Here's a link to the pistons

-> 98mm Max Moritz set for a Short Stroke 3.2

My piston to valve clearance has shown a paltry 1mm. The timing of the cams is 2.2-2.4mm. With this non-radical cam I was surprised but looking at the pistons maybe it makes sense. I think these pistons were designed for the SC cams, they have very shallow valve pockets. I proved the valves are hitting at the pockets by applying some white grease to the valve, reinstalling and doing the clearance check, then seeing the white grease on the valve pockets.

If I set the valve in 1mm and do an entire revolution it's ok, no binding, but at about 1.2mm I get binding. On the other bank I get binding at 1mm. The exhaust clearance is fine (over 2mm).

My question is, how much material can be removed from the pistons? Can I have the shop safely remove .75mm for safe tolerance?

I am running TI retainers with Supertec racing springs.

__________________
'79 SC
Old 09-11-2006, 10:33 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #1 (permalink)
Super Moderator
 
cstreit's Avatar
 
Join Date: Feb 2000
Location: Naperville, IL USA
Posts: 14,967
Garage
That's cutting it pretty close. I don't remember offhand what expansion rates are for these but I think at operating temps you'd be too close for comfort.

I can't tell you what the thickness is in this area, but I can tell you what I did for a customer recently.

He ingested a piece of debris into a hi-strung race motor (running no air filters) and dinged up a very expensive piston pretty good. THere was no time to get new ones made. We sent the piston to Peter Dawe who used some sort of ultra-sound/x-ray/sci-fi thing to actually measure the thickness of the material under the ding to make sure there was sufficient metal under it. You simply could not get a reliable measurement with large calipers.

You might try large calipers first as the Max Mor. pistons have a more standard "regular" shape but short of that, try calling Peter.
__________________
Chris
----------------------------------------------

1996 993 RS Replica
2023 KTM 890 Adventure R
1971 Norton 750 Commando
Alcon Brake Kits
Old 09-11-2006, 09:17 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #2 (permalink)
Registered
 
Join Date: May 2005
Location: Cambridge, Ontario (Ayr)
Posts: 288
The pistons are off to the machine shop. I think the depth can be measured at the valve pockets, I'll soon find out.

Should BOTH exhaust and intake pockets be machined to maintain the balance of the piston?

__________________
'79 SC
Old 09-12-2006, 07:13 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #3 (permalink)
Reply


 


All times are GMT -8. The time now is 04:11 AM.


 
Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2025, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2025 Pelican Parts, LLC - 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.