Help with timing chain wear and camshaft-distributor drive slot question???

Stevehose

Stevehose

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I am on a mission to cure my low rpm timing chain rattle, it's been bothering me for years. I pulled the upper cover off today and my friend (a talented Porsche mechanic) pointed out a few things for the forum experts to answer. First pic, what do you make of the uneven wear marks on the chain rollers-can you see the asymetrical dark areas on the links? Is this normal? I am replacing the chain and sprocket regardless but any ideas on cause? The sprocket still has flat spots on top of the gear (not pointy) so doesn't appear to be worn out.

IMG_0515.jpg



Next up and more concerning is the distributor drive piece at the end of the camshaft. It's a Schrick 284 if that makes a difference. Under screrwdriver pressure (not by hand) the piece that connects to the distributor drive gear turns in the cam. With a screwdriver in either direction, it turns but the cam does not. See video:



Should there be something in the end to prevent rotation or does it need to be tightened in a certain direction (one would think counter clockwise in order to stay tight against the rotation of the cam):

IMG_0521.JPG


Any ideas? Thanks.
 

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well not a lot of ideas here, but i would say, nice oil colour,

on the uneven wear marks, i would say nice catch, i am interested if someone can shed some light, in principle i would expect even uniformly distributed polishing, but...

on the last test, please stop that, first that cut drives the distributor but it is not designed to do viceversa so do not force lever the cam with the screwdriver
second, IMHO, you have losen the cam from the retaining nut, if i am right you have changed the ingnition point

the cam should have a blocking piece so this might not be possible, just my guess

you must consider that moving the whole engine from that small cut in the cam end will be hopeless
 
deQuincey said:
well not a lot of ideas here, but i would say, nice oil colour,

on the uneven wear marks, i would say nice catch, i am interested if someone can shed some light, in principle i would expect even uniformly distributed polishing, but...

on the last test, please stop that, first that cut drives the distributor but it is not designed to do viceversa so do not force lever the cam with the screwdriver
second, IMHO, you have losen the cam from the retaining nut, if i am right you have changed the ingnition point

the cam should have a blocking piece so this might not be possible, just my guess

you must consider that moving the whole engine from that small cut in the cam end will be hopeless
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The nut is tight. The cam is not moving. Only the prong piece inside is moving. We weren’t trying to move the engine with that, we were only trying to take the slack out of the backside of the cam chain. The timing is only effective if that prong moves which it probably doesn’t because it’s fairly snug. Once you set the distributor relatives or that it will be OK. Thanks.
 
deQuincey said:
Imho, beteen the sprocket and the cam there is a steel key to set a fixed position, so it. should not move

if it moves maybe that is reason for rattle
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I agree there should be some sort of key or something keeping it in place and not able to move under any circumstances.
 
deQuincey said:
now i understand so you have a second part as cam end
in my cam it is machined in the same cam
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Yes, this is a separate part that is moving within the cam. @sfdon have you seen anything on these Schricks that would lock that nose piece in places and keep from moving inside the cam?
 
There was a recall on Schrick cams a few years ago. No idea if same time period as your cam install.
I remember it was at 5:22 am that I was contacted from Germany that I was not to start any engine that I had just built but to disassemble the engines and return the cams for replacement. I billed them around 3-5 $k for 3 engines that I took apart and put back together again. Schrick was really good about the whole thing.
you have my phone number.
 
sfdon said:
There was a recall on Schrick cams a few years ago. No idea if same time period as your cam install.
I remember it was at 5:22 am that I was contacted from Germany that I was not to start any engine that I had just built but to disassemble the engines and return the cams for replacement. I billed them around 3-5 $k for 3 engines that I took apart and put back together again. Schrick was really good about the whole thing.
you have my phone number.
Click to expand...

wow !
 
Btw - I have multiple engines on stands right now with Schrick cams.
I can head in to shop today if you want.
 
sfdon said:
Btw - I have multiple engines on stands right now with Schrick cams.
I can head in to shop today if you want.
Click to expand...
I’ll call you tomorrow whenever you’re there, no hurry today it aint goin nowhere :p thanks
 
I’m heading in at 10:00 today.

have you tested your tensioner?
hint- don’t touch it til we talk.
 
The key indexes the flange that the cam gear mounts to. The nut tightens the flange onto the shaft of the cam.
The “fork” of the cam should not move independently of the cam.
Did you test for chain slack?
AFTER testing you can pull the tensioner to inspect for wear but must retension before starting.
 

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It looks like that woodruff key is NLA. Is there a suitable replacement?
 
For the record, the inner fork piece is independent of the rest of the cam, usually the fork and cam are one piece. I'm going to figure out a way to keep it from rotating under any circumstances. There is enough resistance to drive the distributor and gear, but I want no doubt.

Cam.png.png
 
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