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jberger
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Joined: November 17, 2003
Posts: 2476
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 Posted: Mon Aug 15, 2005 11:27 am Post subject: Cam Bearing Thrust Measurement |
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Hi all, 79 CA model 2.0
Does anyone have the thickness of the thrust surfaces on a cam bearing from a new set? Also looking for the measurement between the cam thrust surfaces.
On a side note: The Bentley states that if the cam lifts out of the bearing saddles while rotating the crank backwards (with half the case off) than you must renew the cam gear. I don't know about this, there seems to be no perceptible backlash in the gears but my cam lifts out of the saddles while rotated backwards.
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Amskeptic
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Joined: October 18, 2002
Posts: 8568
Location: All Across The Country
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| Posted: Tue Aug 16, 2005 2:18 pm Post subject: Re: Cam Bearing Thrust Measurement |
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| jberger wrote: |
The Bentley states that if the cam lifts out of the bearing saddles while rotating the crank backwards (with half the case off) than you must renew the cam gear. I don't know about this, there seems to be no perceptible backlash in the gears but my cam lifts out of the saddles while rotated backwards.
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Those two symptoms are in agreement, you cannot use the word "but."
You can use the word "and" however.
>no perceptible backlash in the gears and cam lifts out of the saddles<
This means you have two proofs that the mesh is too tight.
No backlash and walk out means the mesh is too tight.
No backlash and no walk out means it is perfect.
Backlash BUT walks out means you got a problem with gear cuts or surfaces.
Backlash and no walk means you are too loose.
I think Jake Raby has used valve lapping paste to open up the gear swiping surfaces a tad as he sought a friction-free mesh. Clean like you have never cleaned all the paste out of there, then retest.
Colin
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Jake Raby
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Joined: August 23, 2003
Posts: 7433
Location: Aircooled Heaven USA
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| Posted: Tue Aug 16, 2005 2:58 pm Post subject: |
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Generally if the cam bearing thrust is too tight a tap of the cam fore and aft with the thrust bearing in place will give you a different reading thats adequate... Many times these are not settled out of the box.
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Jake Raby
Raby Engine Development
www.rabyenginedevelopment.com
"I've never given anyone Hell, I just told them the truth and they thought it was Hell" |
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jberger
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Joined: November 17, 2003
Posts: 2476
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| Posted: Tue Aug 16, 2005 4:17 pm Post subject: |
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My 10000 mile old thrust bearing has a front thrust surface that measures .010 thinner than the rear.
This teardown is prompted by a strange valvetrain clacking coming from my engine. Found the cam to have .015 end play  All other specs in the case look good. No scoring or chaffing on any bearing surfaces (other than normal wear). Heads good, pistons fine(no skirt slap) blah, blah, blah. I am trying to figure out why #1 my cam bearing thrust surface wore so badly and #2 is my cam ok to reuse? |
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Amskeptic
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Joined: October 18, 2002
Posts: 8568
Location: All Across The Country
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| Posted: Fri Aug 19, 2005 11:33 am Post subject: |
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I bought some Mahle bearings many years ago that were hideously out-of-spec right out of the box, .011" play.
If you have eaten a KNOWN GOOD set of cam bearings then all I can think of is that your helical crank/cam gears drove agains the thrust bearing surfaces, now my question is was that due to loose cam mesh, tight cam mesh, or lousy bearings to begin with?
Colin
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jberger
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Joined: November 17, 2003
Posts: 2476
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| Posted: Fri Aug 19, 2005 11:44 am Post subject: |
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| Amskeptic wrote: |
I bought some Mahle bearings many years ago that were hideously out-of-spec right out of the box, .011" play.
If you have eaten a KNOWN GOOD set of cam bearings then all I can think of is that your helical crank/cam gears drove agains the thrust bearing surfaces, now my question is was that due to loose cam mesh, tight cam mesh, or lousy bearings to begin with?
Colin |
Yes, no, maybe?
Trying to figure that out as well. Quite a puzzle. |
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