Timing Chain, End Play and Cam Button

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RD_Racing
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Timing Chain, End Play and Cam Button

Post by RD_Racing » Sat Dec 16, 2017 5:55 pm

Is the cam timing gear position pretty much located by the crank timing gear? The lower crank gear is a fixed position (press fit) and since the cam timing gear has nothing to hold it in place, doesnt the in/out positon of the cam sprocket get located by the position of the crank gear and the chain thats locating it?
With that said, I just installed a new Solid Roller cam and timing chain (comp #7100) which has a built-in thrush bearing and with the crank gear fully seated, the cam is being pulled out slightly by the chain and my thrush bearing isnt making constant contact with the block.. Also when i put the timing cover on (with the gasket) I have no clearance between the cam button and timing cover because of this too. Is there any way to resolve this?

Sorry, I'm still learning here.. Thanks for any help or explanation

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rustbucket79
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Re: Timing Chain, End Play and Cam Button

Post by rustbucket79 » Sat Dec 16, 2017 6:06 pm

installed with the gasket, that button can run with minimal clearance. (Teflon button)
You can adjust the running clearance by machining down the button, or you can make a slight correction (on a tin front cover) by tapping the cover outwards with a dead blow hammer.

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Re: Timing Chain, End Play and Cam Button

Post by pamotorman » Sat Dec 16, 2017 6:16 pm

first thing to do is use a straight edge on the face of the gears without the chain to see if they are in line. if they do not the chain will wear faster than it should. a stock SBC timing cover needs to be reinforced because it will spring out under pressure from the cam button. some builders shim between the back of water pump and the cover to prevent this. you want .005/.010 end play on the cam

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Re: Timing Chain, End Play and Cam Button

Post by RD_Racing » Sat Dec 16, 2017 6:22 pm

rustbucket79 wrote:
Sat Dec 16, 2017 6:06 pm
installed with the gasket, that button can run with minimal clearance. (Teflon button)
You can adjust the running clearance by machining down the button, or you can make a slight correction (on a tin front cover) by tapping the cover outwards with a dead blow hammer.
Thank you!
So basically let the upper sprocket fall where it does and work off that position? I was planning on using clay and trying to achieve roughly.004 between the cam button and cover.

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Re: Timing Chain, End Play and Cam Button

Post by RD_Racing » Sat Dec 16, 2017 6:53 pm

pamotorman wrote:
Sat Dec 16, 2017 6:16 pm
first thing to do is use a straight edge on the face of the gears without the chain to see if they are in line. if they do not the chain will wear faster than it should. a stock SBC timing cover needs to be reinforced because it will spring out under pressure from the cam button. some builders shim between the back of water pump and the cover to prevent this. you want .005/.010 end play on the cam

Yes I put a straight edge on the 2 gears and they are perfectly inline with each other. With the timing cover off, I can move the cam in/out .080
So I will rotate the motor over a few times and let the upper sprocket neutralize and locate itself and then work off that position..
I have a aftermarket timing cover that is re-inforced for a cam button but it still has allot of flex so I will get a more solid cover..

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Re: Timing Chain, End Play and Cam Button

Post by GOSFAST » Sat Dec 16, 2017 7:23 pm

This is just one of the reasons we've all but eliminated any cam buttons or chasing cam end play on "streeter's" any longer!

We recently designed some tooling allows us to modify the cam thrust surface on those early castings and use the late style thrust plate/screws for assembly. We've actually begun selling the complete installation kits! Can all be done a floor-model drill press.

All it requires is ordering the later stepped-nose cam and bolt it all together, has made our lives here much simpler lately!

Thanks, Gary in N.Y.

P.S. We "prep" the block during the basic machining and use a "Torrington" roller chain (not shown) setup at the end. End play is "built-in" at about .003"/.004". Done a few dozen this past year! That's a 400" SB in the photo below.

SBC Cam Thrust Plate-Late Cam Installed.JPG
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Re: Timing Chain, End Play and Cam Button

Post by RD_Racing » Sat Dec 16, 2017 9:42 pm

Had a friend stop by and tell me I shouldn't use the Teflon cam button with a cast aluminum cover because it will sand it down?

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Re: Timing Chain, End Play and Cam Button

Post by Circlotron » Sat Dec 16, 2017 10:32 pm

I don't have a SBC but looking at these camshaft pictures makes me think that given the angle of the distributor drive gear teeth, once the oil pump adds it's load the cam will try to screw it's way toward the rear of the block. Why the need for a cam button on the front of the cam then?

http://www.edelbrock.com/automotive/mc/ ... y-sb.shtml

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Re: Timing Chain, End Play and Cam Button

Post by lefty o » Sat Dec 16, 2017 10:52 pm

Circlotron wrote:
Sat Dec 16, 2017 10:32 pm
I don't have a SBC but looking at these camshaft pictures makes me think that given the angle of the distributor drive gear teeth, once the oil pump adds it's load the cam will try to screw it's way toward the rear of the block. Why the need for a cam button on the front of the cam then?

http://www.edelbrock.com/automotive/mc/ ... y-sb.shtml
on a roller, a sbc cam will walk around.

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Re: Timing Chain, End Play and Cam Button

Post by MadBill » Sat Dec 16, 2017 11:02 pm

Wear potential depends on whose cover it is. I have a Cloyes one here. It's a two piece unit to permit easy cam adjustment and has the thrust bearing built in and externally adjustable, but the internal surfaces are practically a mirror finish and could not conceivably damage the button with a one piece version. A rough sand cast part might be a different story, but could be ground smooth if necessary.

BTW, by way of background a flat tappet cam is ground with a slight taper to the lobes, which mate with the slight radius (60" -100" curvature) on the lifter faces to promote rotation. the taper also results in a net force holding the cam rearward.

The drag of the oil pump also adds a 'pushback' load, but it can fluctuate, causing the cam and spark timing to vary. I once worked on a prototype Oldsmobile which had been fitted with a roller cam but no thrust plate. The car drove OK, but at idle the spark timing continuously over a +/- 5° range.

As mentioned above, many engines now use a thrust plate for the purpose, which is simple and pretty foolproof.
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Re: Timing Chain, End Play and Cam Button

Post by bigblockmopar » Sun Dec 17, 2017 6:24 am

RD_Racing wrote:
Sat Dec 16, 2017 5:55 pm
Is the cam timing gear position pretty much located by the crank timing gear? The lower crank gear is a fixed position (press fit) and since the cam timing gear has nothing to hold it in place, doesnt the in/out positon of the cam sprocket get located by the position of the crank gear and the chain thats locating it?
...
I don't see this problem really picked up in the replies above.
But, no the crank sprocket does not/should not dictate where/how much the cam sprocket is pulled from the block.
The cam sprocket should ride against the block. The crank sprocket should be pressed against the crank fully. Of course they should both be align with each other this way.
The cam button's end play with make sure the camshaft can only come forward that much during operation, and not more.

If the crank sprocket 'pulls the cam and its sprocket forward' out of the block, then there's something wrong.
Most likely the crank sprocket is not seated all the way onto the crank or it's manufacturered wrong, the cam sprocket boss is machined too much at the back.

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Re: Timing Chain, End Play and Cam Button

Post by Newold1 » Sun Dec 17, 2017 9:35 am

Glad to see someone has put a nice kit and instructions on using a thrust plate on early small blocks. I have been doing that to small blocks for about 20 years now. Much better than using a cam button. I always also have that surface take a thin cut resurface to put it exactly 90 degrees to the main line. You can see the out of square wear patterns on most untouched faces on the back of the thrust plate once run. There was a reason GM switched over in 1987 when they introduced the hydraulic roller as a standard.
All roller cams, solid or hydraulic walk back and forth in an SBC and the thrust plate on a cam cut for such is the best system bar none!

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Re: Timing Chain, End Play and Cam Button

Post by rfoll » Sun Dec 17, 2017 9:52 am

I recently tried to tune a 350 for an inexperienced friend and watched the timing move around a total of over 10 degrees at idle. The original builder failed to use a cam button with his Comp XR294HR hydraulic roller cam. With dished pistons .045" in the hole and a big single plane intake, the car was a dog.
So much to do, so little time...

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Re: Timing Chain, End Play and Cam Button

Post by Walter R. Malik » Sun Dec 17, 2017 9:57 am

I suspect you are using an O.E.M. hydraulic roller cam block but, without the thrust plate with an older type camshaft nose.

The front cam thrust face of a hydraulic roller cam block, (without the thrust plate), and an older flat tappet block, (which requires no thrust plate), are different.
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Re: Timing Chain, End Play and Cam Button

Post by RD_Racing » Sun Dec 17, 2017 11:00 am

This morning I rotated the motor over a few times to let the upper cam sprocket fall where it does. I then put an indicator on the face of the cam sprocket and could push it in .009
The cam gear already has a roller thrust plate built into it, can I just add a regular thrust plate behind it? Comp Cams makes one that is .020 (cant find one thats only .010 thick) and by adding that, it would eliminate all rearward movement and keep constant contact on the block.

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