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
It's a 914 ...
 
stownsen914's Avatar
 
Join Date: Jan 2008
Location: Ossining, NY
Posts: 1,840
Carrera chain tensioners or mechanical for a race engine?

I've heard that the pressure fed Carrera tensioners sometimes fail. I'm rebuilding a race engine this winter that has Carrera tensioners that are approx. 25 years old. A few questions:
Is it possible/necessary to rebuild them?
I read about a safety mechanism for Carrera tensioners that Jerry Woods offers => link. Is that worth doing?
Or never mind the replace the Carrera tensioners with mechanical tensioners and deal with the periodic required adjustment?

Thanks ...

Old 12-14-2019, 07:26 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #1 (permalink)
Registered User
 
Join Date: Jun 2009
Posts: 322
Never seen one fail on a street motor, but track motors stress everything beyond the normal. Also hear that the small metal lines can stress fracture and spew 3 gals of oil out quickly. I have 2 track motors and have solid on one and hydraulic on the other. I have aeroquip for the small steel lines. There are disc like pinch clamps that you can fasten to the tensioner piston as a safety measure. Would not risk my motor on 25 yr old tensioners. I have 2 pair of those sitting on my shelf that I stared at for a moment. Contemplating the catastrophic failure potential, and they are still sitting there. Would like to know if there are viable rebuild kits for them. Bob
Old 12-16-2019, 12:18 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #2 (permalink)
Registered User
 
Walt Fricke's Avatar
 
Join Date: May 2004
Location: Boulder, Colorado
Posts: 5,695
I think that for the most part the Carrera tensioners don't fail. My SC got them in its 2.7 configuration in 1986 or so. I think they moved either to a race 2.7 or to my 3.0, which I got around 1989. Can't recall if it has the pressure feds, but I would have soon added them.

There are no washers or seals internal to the tensioner which you could replace as part of a rebuild. The critical tolerances are the fit of the piston in the bore of the main body. Short of someone making replacement pistons a little larger so you could bore its cylinder (and I doubt anyone makes such a thing), no way to deal with that if it gets worn somehow, and leaks. The top of the piston is a cap, and it is part of the bleed system - as more pressure is applied to the piston, more oil bleeds out a tiny hole on the top side of the piston. I don't see how this could wear.

There are two one way valves. One is external, and determines the pressure in the reservoir compartment. It isn't very well secured mechanically, and if molested the cap part can pop out. I think a guy could tap the hole, drill a hole in a small bolt a bit larger than the spring, and drill a smaller hole through the bolt head. Then you could have a threaded connection, and with a little Loctite or some more clever mechanical fixation (safety wire?), have a valve which would never come out.

The other valve is the same generally - a ball bearing, a spring, and a retention cap, and it prevents pressure in the working chamber from forcing oil back into the reservoir. The only way to fiddle with this is to remove the piston, and all the pressure here is on the ball forcing it down against the drilling in the body to close the entry hole from the reservoir, so there is no significant pressure trying to dislodge its holder.

Springs basically never change rate, though they can shorten (if a coil). Torsion bars can do this by taking a set a bit twisted from when new, but usually I think this is from overloading (like the 2400 pounds of drywall I once hauled in my VW van)rather than just repetition. I'd doubt this happens with these little springs enough to reduce seat pressure so it matters. Certainly not to the internal spring.

It appears that sometimes one of these is a lemon, but I don't think they are a "when" item, but an "if" problem.

Racing isn't going to put enough extra strain on things, seems to me. You build up more miles with a daily driver/vacation car than a track car.

If worried, there is a Jerry Woods fix for the pressure feds which involves inserting a brass tube piece which limits how far the piston can collapse back into its chamber - you can find it described using the search function. Same end result as the clamp collars on the previous generation.
Old 12-16-2019, 04:49 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #3 (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: 6,170
Garage
Adding to what Walt said, here are two threads about Carrera tensioners.

Carrera tensioner questions

Tensioner failure >opinions?<

I had one fail, and I am not sure why. My theory is a small piece of debris got in the bottom check valve.

On my motor with new chains there was not enough room to fit the JW spacers. But then there wasn't enough slop for the chain to skip when the tensioner failed.

Porsche says, if the tensioner is not firm, it must be replaced.

If anyone has successfully rebuilt one, they have yet to speak up.
__________________
Gordon
___________________________________
'71 911 Coupe 3,0L outlawed
#56 PCA Redwood Region, GGR, NASA, Speed SF
Trackrash's Garage :: My Garage
Old 12-16-2019, 06:33 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #4 (permalink)
Registered User
 
Join Date: Aug 2006
Location: So cal
Posts: 119
tensioners

I have a friend who raced his 71 911S 2.2. and when I asked why he did not have Carrera tensioners, his reply was--- I have the updated idler arms and ramps and turbo tensioners and I have never had a problem with my tensioners. So he never got the Carrera's. chris
Old 12-24-2019, 08:10 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #5 (permalink)
Banned
 
Join Date: Dec 2019
Posts: 3
I have 2 pair of those sitting on my shelf that I stared at for a moment. Contemplating the catastrophic failure potential, and they are still sitting there. Would like to know if there are viable rebuild kits for them. Bob
Old 12-30-2019, 04:49 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #6 (permalink)
 
Registered User
 
Join Date: Oct 2008
Location: Nash County, NC.
Posts: 7,379
And at what point are the mechanical tensioner properly adjusted, cold or hot?
Bruce
Old 12-30-2019, 10:28 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #7 (permalink)
Registered User
 
Join Date: Jun 2009
Posts: 322
I don't know if any one has come up with a gauge to accurately check the chain tension, so pretty much by feel. I was told to use a .060'' shim to fit between the rocker foot and adjuster bolt on the solid tensioner engine cold. I roll it over 2-3 times until I determine the tightest chain condition, and then set with a moderate drag on the shim. Run the car up to temp, pull the covers and check the slack/tension in the chain at temp, again at its tightest position. Should have slight flex to it, definitely not stretched tight. If chains are new, will need to redo after a number of hours of service. Before all of this, set the cam timing with the chain at operating temp tension. Bob
Old 12-30-2019, 01:13 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #8 (permalink)
KTL KTL is offline
Schleprock
 
KTL's Avatar
 
Join Date: Sep 2000
Location: Frankfort IL USA
Posts: 16,188
JB Racing has an instruction sheet with their recommendations on setup/adjustment of the mechanical tensioners. Maybe MBruns could chime in since Mike was in charge of the engine shop at JB Racing for many years.

http://www.jbracing.com/tech%20guides/Chain%20Tensioner%20Instructions.pdf
__________________
Kevin L
Present: '86 Carrera, '79 911SC widebody conversion rolling racecar shell
Past: '87 Carrera
Old 12-31-2019, 12:33 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #9 (permalink)
Registered User
 
Walt Fricke's Avatar
 
Join Date: May 2004
Location: Boulder, Colorado
Posts: 5,695
Bittyga - read post 3.

Old 01-01-2020, 02:55 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #10 (permalink)
Reply

Thread Tools
Rate This Thread
Rate This Thread:

 


All times are GMT -8. The time now is 10:13 AM.


 
Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2020, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2020 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.