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
Under the radar
 
Trackrash's Avatar
 
Join Date: May 2007
Location: Sebastopol, the land of wine and redwoods in The Republic of California.
Posts: 5,240
Garage
Bent exhaust valves oh my!

I'm in the process of going through the heads on my rebuild based on a '78 SC motor.

After replaceing the guides and re-surfacing the seats I found that FOUR of my exhaust valves were bent!

The weird thing is there was no evidence of burning, pitting, or grooving of either the valves or seats. They all looked like nicely worn in parts.

AND, there is no evidence of any piston to valve contact.

To be honest one of the valves did have a dark area on the face, but the other three looked like they were properly seated all around the seat. The guides were at the wear limit but not totally shot.

Question; is this common or very weird?

This valve had about .015" run-out.

Here are two valves that apparently were fully seated, but show .010" run-out.

What the seats looked like.


Thoughts? BTW I have no history on this motor beside "it ran when pulled".
And I just ordered 6 new exhaust valves.
__________________
Gordon
___________________________________
'71 911 Coupe 3,0L outlawed
#56 PCA Redwood Region, GGR, NASA, Speed SF
Trackrash's Garage :: My Garage

Last edited by Trackrash; 06-30-2016 at 12:22 PM..
Old 06-30-2016, 12:20 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #1 (permalink)
abit off center
 
cgarr's Avatar
 
Join Date: Feb 2002
Location: At the Airport Kentwood, MI
Posts: 7,046
Garage
Send a message via Yahoo to cgarr
How did it run?? I just got a set of 2.7 heads in that all looked fine but went to grind the exhaust valves and 2 had about the same run out as yours. No evidence of any contact, first one I came across like this besides the obvious bent over valve that hit the piston ones.
__________________
______________________
Craig
G2Performance
Twinplug, head work, case savers, rockers arms, etc.
Old 06-30-2016, 12:46 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #2 (permalink)
Under the radar
 
Trackrash's Avatar
 
Join Date: May 2007
Location: Sebastopol, the land of wine and redwoods in The Republic of California.
Posts: 5,240
Garage
When I bought the motor it was on a pallet. So no history other than it "Turns freely"

The only other thing was it had back dated exhaust and oil lines and it probably came out of a wrecked long hood. Not that that makes a difference.
__________________
Gordon
___________________________________
'71 911 Coupe 3,0L outlawed
#56 PCA Redwood Region, GGR, NASA, Speed SF
Trackrash's Garage :: My Garage

Last edited by Trackrash; 06-30-2016 at 12:56 PM..
Old 06-30-2016, 12:53 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #3 (permalink)
Registered User
 
Join Date: Jul 2001
Location: Portland Oregon
Posts: 6,992
Someone missed a shift and tagged the valves with the pistons.
__________________
Steve Weiner
Rennsport Systems
Portland Oregon
(503) 244-0990
porsche@rennsportsystems.com
www.rennsportsystems.com
Old 06-30-2016, 03:29 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #4 (permalink)
Under the radar
 
Trackrash's Avatar
 
Join Date: May 2007
Location: Sebastopol, the land of wine and redwoods in The Republic of California.
Posts: 5,240
Garage
Quote:
Originally Posted by Steve@Rennsport View Post
Someone missed a shift and tagged the valves with the pistons.
And kept driving like it never happened....

That was my thought. Probably happened long before the motor was in my possession.

It's just weird that three of the four seemed to still be properly seated.
__________________
Gordon
___________________________________
'71 911 Coupe 3,0L outlawed
#56 PCA Redwood Region, GGR, NASA, Speed SF
Trackrash's Garage :: My Garage
Old 06-30-2016, 04:34 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #5 (permalink)
Registered User
 
Join Date: Jul 2001
Location: Portland Oregon
Posts: 6,992
Quote:
Originally Posted by Trackrash View Post
And kept driving like it never happened....

That was my thought. Probably happened long before the motor was in my possession.

It's just weird that three of the four seemed to still be properly seated.
I see this fairly often with heads that are sent here for rebuild. Most people don't notice and/or don't want to spend the money to fix it properly.

Just another can that gets kicked down the road.
__________________
Steve Weiner
Rennsport Systems
Portland Oregon
(503) 244-0990
porsche@rennsportsystems.com
www.rennsportsystems.com
Old 06-30-2016, 06:14 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #6 (permalink)
 
Member 911 Anonymous
 
DRACO A5OG's Avatar
 
Join Date: Sep 2007
Location: Rancho Palos Verdes
Posts: 14,289
Garage
Send a message via Skype™ to DRACO A5OG
holy poop, that sucks a cancer on their house!
__________________
'85 Carrera Targa
Factory Marble Grey/Black * Turbo Tail * 930 Steering Wheel* Sport Seats * 17" Fuchs (r) * 3.4 * 964 Cams * 915 * LSD * Factory SS * Turbo Tie Rods * Bilsteins * Euro Pre-Muff * SW Chip on 4K DME * NGK * Sienes GSK * Targa Body Brace
PCA/POC
Old 07-01-2016, 03:14 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #7 (permalink)
Under the radar
 
Trackrash's Avatar
 
Join Date: May 2007
Location: Sebastopol, the land of wine and redwoods in The Republic of California.
Posts: 5,240
Garage
Quote:
Originally Posted by DRACO A5OG View Post
holy poop, that sucks a cancer on their house!
Actually not a real big deal to replace all the exhaust valves, in the big scheme of things. Just glad I noticed, and new valves are a good thing.
__________________
Gordon
___________________________________
'71 911 Coupe 3,0L outlawed
#56 PCA Redwood Region, GGR, NASA, Speed SF
Trackrash's Garage :: My Garage
Old 07-01-2016, 04:12 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #8 (permalink)
Member 911 Anonymous
 
DRACO A5OG's Avatar
 
Join Date: Sep 2007
Location: Rancho Palos Verdes
Posts: 14,289
Garage
Send a message via Skype™ to DRACO A5OG
Yes, lucky you found it now vs later.

I am having my moments of cursing their children and children's children on my 964 Cam Swap. I mean what the fudge, how hard is it to get close to proper timing of 1.25MM. I found it to be 1.10MM and 0.85MM and all rocker shafts were miss-aligned, no wonder she was a lazy dog.
__________________
'85 Carrera Targa
Factory Marble Grey/Black * Turbo Tail * 930 Steering Wheel* Sport Seats * 17" Fuchs (r) * 3.4 * 964 Cams * 915 * LSD * Factory SS * Turbo Tie Rods * Bilsteins * Euro Pre-Muff * SW Chip on 4K DME * NGK * Sienes GSK * Targa Body Brace
PCA/POC
Old 07-01-2016, 09:58 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #9 (permalink)
Registered User
 
Join Date: Aug 2010
Location: Küsten, Germany
Posts: 175
Are you sure your jaw chuck really runs true?
To measure valve truth and roundness i would rather use a collet chuck on a lathe...

The one valve having a dark area on its seat surface may really be bent or not having rotated during operation on an out of round valve seat.
Old 07-02-2016, 06:32 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #10 (permalink)
Registered User
 
Join Date: Feb 2004
Location: UK
Posts: 2,231
I would think that a 3-jaw scroll chuck would run out by around 0.003" at the worst .

A good quality chuck like a Pratt Burnerd may be 0.001".

It would be quite easy to check with something like a 3/8" drill centre gripped in the chuck to see what is happening,
Old 07-02-2016, 06:47 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #11 (permalink)
Functionista
 
manbridge 74's Avatar
 
Join Date: Jul 2011
Location: CO
Posts: 5,298
I would think .010 would be noticeable rolling the valve on something flat like plate glass.
__________________
Jeff
74 911, #3
I do not disbelieve in anything. I start from the premise that everything is true until proved false. Everything is possible.
Old 07-02-2016, 07:52 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #12 (permalink)
Under the radar
 
Trackrash's Avatar
 
Join Date: May 2007
Location: Sebastopol, the land of wine and redwoods in The Republic of California.
Posts: 5,240
Garage
Quote:
Originally Posted by crummasel View Post
Are you sure your jaw chuck really runs true?
To measure valve truth and roundness i would rather use a collet chuck on a lathe...

The one valve having a dark area on its seat surface may really be bent or not having rotated during operation on an out of round valve seat.
I took that into account. That chuck is close, but not perfect to be sure.

I put all my valves in that chuck just as a double check. All the intakes and two of the exhaust valves ran true.

I considered re-facing the two not so bad exhausts, but for <$30 a pop not worth taking the chance. Especially when Porsche says replace any bent valves.

Quote:
Originally Posted by manbridge 74 View Post
I would think .010 would be noticeable rolling the valve on something flat like plate glass.
Yes the four bent valves wobbled noticeably.
__________________
Gordon
___________________________________
'71 911 Coupe 3,0L outlawed
#56 PCA Redwood Region, GGR, NASA, Speed SF
Trackrash's Garage :: My Garage

Last edited by Trackrash; 07-02-2016 at 08:13 AM..
Old 07-02-2016, 08:11 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #13 (permalink)
Registered User
 
prschmn's Avatar
 
Join Date: Feb 2007
Location: Northeast
Posts: 379
Not hard to bend exhaust valves due to weak tensioners either--the cams retard when on decel and bango.
__________________
Mark
www.exotechpower.com
1981 Targa-messed with. 91 C2 supercharged track rat
97 Van dieman F2000-gone but not forgotten
30 plus years of rebuilding services
Old 07-05-2016, 02:14 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #14 (permalink)
Reply

Thread Tools
Rate This Thread
Rate This Thread:

 


All times are GMT -8. The time now is 01:01 AM.


 
Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2018 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.