Help needed - slipping cam gear - UPDATED
Rennlist Member
Joined: Oct 2003
Posts: 1,094
Likes: 11
From: St. Louis, MO
Isn't that hex washer cupped a bit? The cupped portion should face the cam gear so that as the bolt tightens against it, it flattens out and bites the gear. If it was flipped over with the cupped portion toward the bolt, it would not flatten out and bite into the gear. This would allow the gear to slip.
I am going from memory, so the cupped washer feature might not be accurate.
I am going from memory, so the cupped washer feature might not be accurate.
Thread Starter
928 Engine Re-Re-Rebuild Specialist
Rennlist Member
Rennlist Member
Joined: Oct 2001
Posts: 7,972
Likes: 34
From: Brighton, MI
Originally Posted by byrdman454
Isn't that hex washer cupped a bit? The cupped portion should face the cam gear so that as the bolt tightens against it, it flattens out and bites the gear. If it was flipped over with the cupped portion toward the bolt, it would not flatten out and bite into the gear. This would allow the gear to slip.
I am going from memory, so the cupped washer feature might not be accurate.
I am going from memory, so the cupped washer feature might not be accurate.
Inventor
Rennlist Member
Rennlist Member
Joined: Sep 2002
Posts: 10,218
Likes: 468
The washer is flat. BTW, the bolt is 55mm long on 32V engines - the torque is 47ft.lbs.
Was the hub on the damaged cam? If the hub is expanding under compression, you should be able to see the crack.
Was the hub on the damaged cam? If the hub is expanding under compression, you should be able to see the crack.
Thread Starter
928 Engine Re-Re-Rebuild Specialist
Rennlist Member
Rennlist Member
Joined: Oct 2001
Posts: 7,972
Likes: 34
From: Brighton, MI
Originally Posted by PorKen
The washer is flat. BTW, the bolt is 55mm long on 32V engines - the torque is 47ft.lbs.
Was the hub on the damaged cam? If the hub is expanding under compression, you should be able to see the crack.
Was the hub on the damaged cam? If the hub is expanding under compression, you should be able to see the crack.
Thread Starter
928 Engine Re-Re-Rebuild Specialist
Rennlist Member
Rennlist Member
Joined: Oct 2001
Posts: 7,972
Likes: 34
From: Brighton, MI
Using a dial caliper I found some interesting differences, but I'm not certain whether they're causing the problem.
1. The "new" cam I am using has a slightly shallower hole.
2. The two cam bolts are not the same length
3. The dog gear behind the cam gear is not broken, but I replaced it anyway.
4. The cam gear is not broken, but I replaced it anyway.
I used the shorter bolt with a different dog and cam gears. This time the cam timing stayed in place for 2 full (360*) revolutions of the crank. It slipped again on the third trip around.
I'm cutting about 3/8" off of my cambolt and trying again tomorrow.
1. The "new" cam I am using has a slightly shallower hole.
2. The two cam bolts are not the same length
3. The dog gear behind the cam gear is not broken, but I replaced it anyway.
4. The cam gear is not broken, but I replaced it anyway.
I used the shorter bolt with a different dog and cam gears. This time the cam timing stayed in place for 2 full (360*) revolutions of the crank. It slipped again on the third trip around.
I'm cutting about 3/8" off of my cambolt and trying again tomorrow.
Rennlist Member
Joined: Dec 2002
Posts: 5,283
Likes: 52
From: Australia
I hope you meant 3mm , not 3/8" , or 10mm????
This sounds as scary as stripping a head bolt thread in an alloy block.......camshaft noses have been known to break off, but usually on a 16V engine. With Ken's stuff, isnt the thickness of the dog less for those that fit a 16V car? You dont have one of those do you, or this not relevant?
jp 83 Euro S AT 50k
This sounds as scary as stripping a head bolt thread in an alloy block.......camshaft noses have been known to break off, but usually on a 16V engine. With Ken's stuff, isnt the thickness of the dog less for those that fit a 16V car? You dont have one of those do you, or this not relevant?
jp 83 Euro S AT 50k
Nordschleife Master
Joined: Dec 2004
Posts: 6,164
Likes: 7
From: Guelph, Ontario, Canada
Dave,
In the second last picture, take the washer and install it just like you have now. Then measure from the dog face to the washer. Then take the cam and measure the thickness. There should be a difference of at least 3mm (the space between the washer and the dog face should be minimum 3mm shorter than the width of the cam gear)
In the second last picture, take the washer and install it just like you have now. Then measure from the dog face to the washer. Then take the cam and measure the thickness. There should be a difference of at least 3mm (the space between the washer and the dog face should be minimum 3mm shorter than the width of the cam gear)
Rennlist Stories
The Best Porsche Posts for Porsche Enthusiasts
9 Features and Characteristics That Only Porsche People Understand
Verdad Gallardo
I've Written 500 Rennlist Articles: Here's How Porsche Has Changed Along the Way
Joe Kucinski
10 Most Unnecessary Porsches Ever Built (And Why We Love Them)
Verdad Gallardo
Porsche 911 GT3 S/C vs 718 Spyder RS: 10 Categories, One Winner
Joe Kucinski
This Builder Is Turning Heads With Its Slantnose 911 Creation
Verdad Gallardo
Porsche 911 GT3 Artisan Edition Pays Homage to Japanese Culture
Verdad Gallardo
Porsche Reveals Coupe Variant of the Electric Cayenne With a Fresh Look
Verdad Gallardo
10 Porsche Colors That Have More Personality Than Most People
Verdad Gallardo
Guntherwerks' Final Speedster Creation Is the Ultimate Porsche Restomod
Verdad Gallardo
Thread Starter
928 Engine Re-Re-Rebuild Specialist
Rennlist Member
Rennlist Member
Joined: Oct 2001
Posts: 7,972
Likes: 34
From: Brighton, MI
Originally Posted by jpitman2
I hope you meant 3mm , not 3/8" , or 10mm????
This sounds as scary as stripping a head bolt thread in an alloy block.......camshaft noses have been known to break off, but usually on a 16V engine. With Ken's stuff, isnt the thickness of the dog less for those that fit a 16V car? You dont have one of those do you, or this not relevant?
jp 83 Euro S AT 50k
This sounds as scary as stripping a head bolt thread in an alloy block.......camshaft noses have been known to break off, but usually on a 16V engine. With Ken's stuff, isnt the thickness of the dog less for those that fit a 16V car? You dont have one of those do you, or this not relevant?
jp 83 Euro S AT 50k
Not sure about the 16v dogs. I actually have 2 spares, and they are all the same thickness, including the dog currently on my cam.
Captain Obvious
Super User
Super User
Joined: Aug 2003
Posts: 22,846
Likes: 348
From: Cambridge, Ontario, Canada
Before you cut anything, get another washer (same or close to the same thickness as what you are planning on cutting off) and install it with the original washer. Then do the rotation testing and see if the timing stays put. If it does then you know the length of the bolt is the problem and you can safely trim it. If not then at least you didn’t cut the bolt for nothing.
Thread Starter
928 Engine Re-Re-Rebuild Specialist
Rennlist Member
Rennlist Member
Joined: Oct 2001
Posts: 7,972
Likes: 34
From: Brighton, MI
Originally Posted by Imo000
Before you cut anything, get another washer (same or close to the same thickness as what you are planning on cutting off) and install it with the original washer. Then do the rotation testing and see if the timing stays put. If it does then you know the length of the bolt is the problem and you can safely trim it. If not then at least you didn’t cut the bolt for nothing.
That's a good idea, though. I'll give it a try.
Thread Starter
928 Engine Re-Re-Rebuild Specialist
Rennlist Member
Rennlist Member
Joined: Oct 2001
Posts: 7,972
Likes: 34
From: Brighton, MI
Originally Posted by heinrich
Dave shouldn't we be wondering why the cams are different? Ar there other differences also?
What's interesting to note is that I have been using cam gears that were re-coated to replace the original finish that was eroding. That recoating covered the entire gear (including the back of the gear which has a very sublte textured spiral finish). I had no slippage issues whatsoever using this recoated gear when I did the last engine pull/fix. Rather than wonder whether this coating is contributing to the slippage, I'm sanding it off of every surface that will have clamping pressure from the cambolt and dog gear. Together with a slightly shorter bolt, this ought to stop the slipping.
Supercharged
Rennlist Member
Rennlist Member
Joined: May 2002
Posts: 18,926
Likes: 88
From: Back in Michigan - Full time!
I know people are going to ask...
https://rennlist.com/forums/928-forum/219673-melted-cam-gears-pics-not-for-the-squeamish.html
The coating is DFL-1 - you can find it here. http://www.techlinecoatings.com/Engine.htm
https://rennlist.com/forums/928-forum/219673-melted-cam-gears-pics-not-for-the-squeamish.html
The coating is DFL-1 - you can find it here. http://www.techlinecoatings.com/Engine.htm