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B20 Cam End Play question

blackbird939

New member
Joined
Sep 8, 2015
Location
Orlando
I have a question about how cam end play is set. Just to understand how it works. Here's what I can get from looking at it all.
The cam sprocket 'hub' has a machined surface on the front and rear, the rear being the most critical. The rear face of the sprocket will interfere with the steel spacer ring when torqued down. This allows the cam sprocket to be tightened and locked into place on the cam.
So, the steel spacer ring, when installed, must be proud of the surface of the the thrust plate by the min/max end play spec. - The difference between the protrusion of the ring past the thrust plate determines the end play. Right? I know there are other factors, like the cam sprocket backlash and alignment of the gears. Those two are within allowable values. However, there's a very tiny step there where the spacer ring has eaten a bit of the steel cam sprocket. I think this was caused by the excessive end play in my B20, 2MM-4mm maybe. Tossed the old brass thrust plate, warped and heavily gouged. Bought a new steel one from IPD. So, now, there is NO end play when torqued down. The sprocket is just touching the thrust plate.

I can either spend another $550 on another set of steel gears, but these are fine, just a small step where the steel ring has etched the rear face of the sprocket. I could shim the spacer ring, have a new taller one made, or mill the thrust plate.

Suggestions?
 
I had a similar problem and was able to get a thicker spacer ring from Eric (hiperfauto). Makes me think that they are available in different thicknesses.
 
How did the spacer wear a groove in the cam gear? Those two things are not supposed to move relative to each other - the spacer is firmly clamped in between the gear and the cam snout. Was the gear coming loose?
 
I had a similar problem about 5 years ago with a set of steel timing gears that I bought from VP except I managed to do what I consider irreparable damage to both the thrust plate and the back of the cam gear. I mean I f'ed those things up and all I did was install the gear and I used the Volvo OE cam gear installation tool.

Since I was in a rush to finish a rebuilt engine, I didn't take the time to figure out what happened, and I installed an NOS set of OE made in Germany SWAG steel timing gears without issue.

Can you post pictures of the damaged thrust plate and both sides of the cam gear?

What is most critical is that the thrust flange is flat and not bent and that spacer ring is thicker than the thrust flange.

Did the cam plug in the back of the engine get changed?
 
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I had a similar problem about 5 years ago with a set of steel timing gears that I bought from VP except I managed to do what I consider irreparable damage to both the thrust plate and the back of the cam gear. I mean I f'ed those things up and all I did was install the gear and I used the Volvo OE cam gear installation tool.

Since I was in a rush to finish a rebuilt engine, I didn't take the time to figure out what happened, and I installed an NOS set of OE made in Germany SWAG steel timing gears without issue.

Can you post pictures of the damaged thrust plate and both sides of the cam gear?

What is most critical is that the thrust flange is flat and not bent and that spacer ring is thicker than the thrust flange.

Did the cam plug in the back of the engine get changed?

The PO had the engine 'rebuilt' about 3k miles ago. I was getting all sort of bad timing, vacuum gauge errors you name it. Then, I rebuilt it about 100 miles ago. Everything seemed fine, I used the same old brass thrust plate. But I never checked the end play. I made the assumption that it was just right, since it was just rebuilt. Well, it developed a tick, then a tap, then a rap. I did everything you can do to it with no luck, aside from tearing it all down again. Everything seems to be in spec. New just about everything, except those steel gears and that old brass plate. The end play was so huge, you could pull the cam gear out at least 2mm, but probably more. My theory is that the tick was the cam being thrust forward and back against that plate, and the distributor gear. The distro gear shows some shiny spot, but not really measurable via fingernail, etc. So, with the new thrust plate, I got zero end play. Closer look, a very slight step is present on the back of the cam sprocket right where the ring would go. I bought some shim stock today. Figured I would just make a very small adjustment to the old brass thrust plate( flip it around as someone said). Hoping and praying that this was the tap. The whole motor down to the valve guides has been gone over now.
 
How did the spacer wear a groove in the cam gear? Those two things are not supposed to move relative to each other - the spacer is firmly clamped in between the gear and the cam snout. Was the gear coming loose?

This is a great question. I have no idea either. The motor came from a never-off-the-road since 1971 car with 350K miles. Who knows what stories that plate could tell, how many hands had touched it.
 
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