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 User
 
Join Date: Jun 2004
Location: Rio Rancho, New Mexico
Posts: 1,326
The marks on the pistons are telling us the exhaust valves tapped the pistons. If the cams were set at 1.4mm the exhaust valves would have been closed and the intake valves open. I'm going by the specs in Bruce Andersons "Porsche 911 Performance Handbook", pages 110 & 111. Please notice if the cams were set up to '76-'77 Carrera specs, 0.9mm to 1.1mm the exhaust valves would be open slightly more than the intake valves at cross-over. That is the exhaust closes at 3 degrees after TDC while the intake opens at 1 degree before TDC. From this info it looks to me as if your cams were retarded upon initial set-up. That is they were set LESS than 0.9mm. Anything over 1.1mm and the intakes would have been open more than the exhausts, and the marks would be on the intake side of the pistons. Timed at 1.4mm the exhaust valves close 3 degrees before TDC and the intakes have opened at 7 degrees before TDC. Since both sides were marked the same indicates both cams were retarded. It is unlikely both cams jumped at the same time. That's my 2 cents. Good Luck.
__________________
DOUG
'76 911S 2.7, webers, solex cams, JE pistons, '74 exhaust, 23 & 28 torsion bars, 930 calipers & rotors, Hoosiers on 8's & 9's.
'85 911 Carrera, stock, just painted, Orient Red
Old 03-28-2005, 11:15 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #21 (permalink)
Registered User
 
Join Date: Dec 2002
Location: Seattle
Posts: 660
2.7 Racer,

Good points and analysis. But what would explain the "apparent" sudden failure at modest RPM after 700 miles of (reportedly successful) driving? I agree with the unlikelihood of two simultaneous cam train failures, one on each side. Any chance of some strange failure of the intermediate shaft gearing that would have affected both sides? I guess the owner needs to give us some more info. If there was no catastrophic internal failure in the cam train then there was either an over rev (which the owner says didn't happen) or both cams were timed wrong (and timed the same, perhaps retarded), as you point out. But if so, wouldn't you think that the engine, during its 700 miles would have run noticeably poorly? And if there was no shift in that timing during that period, why would the valves suddenly be in contact with the pistons at the 700 mile mark? I suppose it's possible that there actually was some contact between pistons and valves prior to that point, which wasn't noticed or mentioned by the owner. This failure may have been more progressive than first thought. If after repeated contact between valves and pistons, maybe it broke a rocker arm and he lost a cylinder, which would certainly get his attention.

Interesting failure; I hope we hear what the resolution is.

Last edited by Rob 930; 03-29-2005 at 01:54 PM..
Old 03-29-2005, 01:46 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #22 (permalink)
Macht Schnell
 
les_garten's Avatar
 
Join Date: Jun 2003
Location: PSL, FL
Posts: 861
Hello,
The engine had suffered during some spirited break in a decrease in performance. I now look back and say that I am not absolutely sure of no over -rev. I have drivin the car much harder in it's history. There was no other damge than the four valve hits. The exhausts for 2 and 5 were hung open and I believe will ultimated be deemed seized. I think the stoppage was about the time these two probably seized from overheating. No rocker damage. The cam sprockets were torqued down. Chains looked good. It may have been a poor valve timing job combined with a relative over rev.
__________________
---Les Garten---85 930, Andial IC, GHL Headers, Fabspeed Dual, K-27 HF2, 3.4 JE Full Finned 7.5:1 CR, 964 CAM'd, Carerra 3.2 Manifold Cut/Flipped, Tec3r, Siemans 55#, GSF Fuel Rails, Clewett Crank Trigger, Clewett Cam Trigger,Dual Plugged, ARP Head Studs/Rod Bolts, Clewett Wires.Tial 46mm WG, Tial 50mm BOV, WEVO Shifter,934 Boost Gauge, Wideband EGO Sensor/Gauge, C2T Head Gaskets, '88 MB 300TE,BMW R100RT
Old 03-29-2005, 01:59 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #23 (permalink)
Forced Induction Junkie
 
WERK I's Avatar
 
Join Date: Jan 2003
Location: Wisconsin
Posts: 3,291
Garage
les_garden,
Have you inspected the valve train, such as cam lobes, springs, retainers? Are the lobes shiney or black/pitted?
During your rebuild, did you have head work performed(heads flycut, valve guides, seats, etc.)
__________________
Dave
'85 930 Factory Special Wishes Flachbau
Werk I Zuffenhausen 3.3l/330BHP Engine with Sonderwunsch Cams, FabSpeed Headers, Kokeln IC, Twin Plugged Electromotive Crankfire, Tial Wastegate(0.8 Bar), K27 Hybrid Turbo, Ruf Twin-tip Muffler, Fikse FM-5's 8&10x17, 8:41 R&P
Old 03-29-2005, 04:02 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #24 (permalink)
Registered User
 
Join Date: Jun 2004
Location: Rio Rancho, New Mexico
Posts: 1,326
Looks like Les is getting closer to understanding what happened. Two exhaust valves hung open. This seems to explain why the motor ran for 700 miles before failure. The slight possible retarding of the cams upon initial timing would not necessarily show up with poor motor performance.
Upon reflection, I'm more inclined to believe a overheating issue is more to blame for this failure. The stuck exhaust valves are telling us something. No broken rockers combined with unbroken, unbent valves leads me to sticking exhaust valves. All this is merely speculation on my part. But further information should narrow this down to the true cause. Fortunately the motor didn't destroy itself. I'm sure once rebuilt this motor will be fun.
__________________
DOUG
'76 911S 2.7, webers, solex cams, JE pistons, '74 exhaust, 23 & 28 torsion bars, 930 calipers & rotors, Hoosiers on 8's & 9's.
'85 911 Carrera, stock, just painted, Orient Red
Old 03-29-2005, 04:55 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #25 (permalink)
Macht Schnell
 
les_garten's Avatar
 
Join Date: Jun 2003
Location: PSL, FL
Posts: 861
Hello,
I am setting up the new pistons and cylinders (3.4L). Upon measuring deck height with a .25MM base gasket, I found I was short on my deck height from .010 to ,.020" in deck height. I had the rods reconditioned during the last rebuild and I believe I lost some height there. I re-shimmed with a .5 mm Base gaseket and the needed deck height was acheived. This may have caused my valve clearance issues before.
__________________
---Les Garten---85 930, Andial IC, GHL Headers, Fabspeed Dual, K-27 HF2, 3.4 JE Full Finned 7.5:1 CR, 964 CAM'd, Carerra 3.2 Manifold Cut/Flipped, Tec3r, Siemans 55#, GSF Fuel Rails, Clewett Crank Trigger, Clewett Cam Trigger,Dual Plugged, ARP Head Studs/Rod Bolts, Clewett Wires.Tial 46mm WG, Tial 50mm BOV, WEVO Shifter,934 Boost Gauge, Wideband EGO Sensor/Gauge, C2T Head Gaskets, '88 MB 300TE,BMW R100RT
Old 04-10-2005, 02:45 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #26 (permalink)
 
Registered User
 
john walker's workshop's Avatar
 
Join Date: Mar 2001
Location: Marysville Wa.
Posts: 17,472
0.25mm really isn't much you know. i can't believe that would make or break it. so were the exhaust valves stuck/tight in the guides?
__________________
8009 103rd pl ne Marysville Wa 98270
206 637 4071
Old 04-10-2005, 03:55 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #27 (permalink)
Author of "101 Projects"
 
Wayne 962's Avatar
Make sure you have a copy of my book, and do the piston / valve clearance check on it this time.

Sounds like this may have been caused by improper setting of the cam timing, combined with a hot engine, and a slight overrev (perfect storm).

-Wayne
__________________
Wayne R. Dempsey, Founder, Pelican Parts Inc., and Author of:
101 Projects for Your BMW 3-Series 101 Projects for Your Porsche 911 How to Rebuild & Modify Porsche 911 Engines 101 Projects for Your Porsche Boxster & Cayman 101 Projects for Your Porsche 996 / 997 SPEED READ: Porsche 911 (October 2018)

Check out our new site: Dempsey Motorsports
Old 04-10-2005, 05:07 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #28 (permalink)
Registered User
 
350HP930's Avatar
 
Join Date: Jun 2003
Location: St Petersburg, FL
Posts: 3,814
Quote:
Originally posted by les_garten
. .
I had the rods reconditioned during the last rebuild and I believe I lost some height there.
Unless the machine shop tried to offset the pin bushing the rod should ould be slighly shorter after reconditioning, increasing deck height instead of decreasing it.
Old 04-10-2005, 08:02 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #29 (permalink)
Macht Schnell
 
les_garten's Avatar
 
Join Date: Jun 2003
Location: PSL, FL
Posts: 861
I have your book Wayne. Awesome. Should have followed it better. Some of it I felt was un-necessary. Ohh Welll!! Expensive lesson learned.
__________________
---Les Garten---85 930, Andial IC, GHL Headers, Fabspeed Dual, K-27 HF2, 3.4 JE Full Finned 7.5:1 CR, 964 CAM'd, Carerra 3.2 Manifold Cut/Flipped, Tec3r, Siemans 55#, GSF Fuel Rails, Clewett Crank Trigger, Clewett Cam Trigger,Dual Plugged, ARP Head Studs/Rod Bolts, Clewett Wires.Tial 46mm WG, Tial 50mm BOV, WEVO Shifter,934 Boost Gauge, Wideband EGO Sensor/Gauge, C2T Head Gaskets, '88 MB 300TE,BMW R100RT
Old 04-11-2005, 07:55 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #30 (permalink)
Registered User
 
Join Date: Apr 2002
Location: Concord, NC
Posts: 810
Les:

Last week I overrevved my engine (missed a shift from 3rd to 4th, went to 2nd, ended my day at the track).

Anyway, my gouges in my pistons look much like yours, and measure between 38-58 thousandths deep depending on the cylinder.

So I'm wondering, are you replacing your pistons?

My pistons and cylinders are brand new (1200 miles) so I hate to replace them, but not sure if I'll sleep at night if I re-use them.

I have decided to replace the rod bearings also, and have my rods measured. My engine revved to a whopping 8800 RPM so it took quite a beating.

Brian
__________________
Brian Keith Smith
Competition Custom Paint
1983 930
My Track Videos
TEC3 EFI Conversion on 1983 930
Old 04-11-2005, 10:40 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #31 (permalink)
Registered User
 
john walker's workshop's Avatar
 
Join Date: Mar 2001
Location: Marysville Wa.
Posts: 17,472
the pistons should be fine. be sure the compression ring still has clearance in it's groove below the notched area, and smooth the notch of any roughness.
__________________
8009 103rd pl ne Marysville Wa 98270
206 637 4071
Old 04-11-2005, 11:31 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #32 (permalink)
Registered User
 
Join Date: Apr 2002
Location: Concord, NC
Posts: 810
John:

Are you responding to my post or Les's post???

Thanks,

Brian
__________________
Brian Keith Smith
Competition Custom Paint
1983 930
My Track Videos
TEC3 EFI Conversion on 1983 930
Old 04-11-2005, 11:36 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #33 (permalink)
Registered User
 
john walker's workshop's Avatar
 
Join Date: Mar 2001
Location: Marysville Wa.
Posts: 17,472
yours, but same for les.
__________________
8009 103rd pl ne Marysville Wa 98270
206 637 4071
Old 04-11-2005, 11:47 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #34 (permalink)
Macht Schnell
 
les_garten's Avatar
 
Join Date: Jun 2003
Location: PSL, FL
Posts: 861
I'm going back in with a 3.4 L P/C kit
__________________
---Les Garten---85 930, Andial IC, GHL Headers, Fabspeed Dual, K-27 HF2, 3.4 JE Full Finned 7.5:1 CR, 964 CAM'd, Carerra 3.2 Manifold Cut/Flipped, Tec3r, Siemans 55#, GSF Fuel Rails, Clewett Crank Trigger, Clewett Cam Trigger,Dual Plugged, ARP Head Studs/Rod Bolts, Clewett Wires.Tial 46mm WG, Tial 50mm BOV, WEVO Shifter,934 Boost Gauge, Wideband EGO Sensor/Gauge, C2T Head Gaskets, '88 MB 300TE,BMW R100RT
Old 04-11-2005, 11:58 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #35 (permalink)
D Troop 3/5 Air cav,162
 
afterburn 549's Avatar
 
Join Date: Jul 2003
Location: Army, Retrograded
Posts: 12,733
mabe i missed it but take a close look at your gear on the intermediat shaft
Old 04-13-2005, 10:55 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #36 (permalink)
Reply

Thread Tools
Rate This Thread
Rate This Thread:

 


All times are GMT -8. The time now is 04:23 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.