Miking the cam

[AManNamedNoah]

In the process of measuring lobe lift on my camshaft. I’m doing this simply by using a micrometer on a stock 140 cam. My question is one of tolerance. In the back of the manual it’s states the lobe lift should be .260 but it never says anything about tolerance. I’m getting values that vary from .255 to .258 depending on the lobe. Are these acceptable?


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[terribleted]

If you are there (The cam is out in your hand) I would just recommend replacement. If you kept the old lifters and intend to use them AND you have them marked so they can go back in the same spot they were you might be fine, but, if new lifters are installed there will be new cam wear as the lifters and cam wear in to each other. You may or may not be ok after this happens. It is an involved deal as you know to go back and change a cam in a Corvair engine. This is why I recommend a new camshaft. If I am all the way into an engine and there is any cam or any lifter wear at all I simply replace both as a failure in this area is a big undertaking to fix. Well worth the additional cost IMO to avoid this possibility.

[AManNamedNoah]

Thanks Ted, I think I’m gonna do the same and probably go with an Isky 260 and a stock cam gear bc I haven’t altered the heads. Is it possible to reuse a cam gear and have it pressed onto an aftermarket cam shaft?


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[terribleted]

Thanks Ted, I think I’m gonna do the same and probably go with an Isky 260 and a stock cam gear bc I haven’t altered the heads. Is it possible to reuse a cam gear and have it pressed onto an aftermarket cam shaft?


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I usually go new cam and new gear. I have dealt with a couple old cam gear failures recently. have not had a new one that I have installed fail that I know of. I generally buy a cam from Clark's with new gear mounted Fail safe setup might be a good idea as well. I have used both failsafe and non-failsafe. I have little trust of any machine shops around here to properly mount the gear and for the trouble of running around to get that done etc. I just order what I want and it magically appears at the garage door:)

[AManNamedNoah]

Good to know. Definitely going to go with a new gear too then. Thanks!


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[nirvairna]

A new cast gear should be fine for a stocker especially with a 260 cam. As far as measuring the peak lift of the cam lobe, it's not square on the top, but ground with a slight slope to induce lifter rotation. Your initial measurements are typical of what I have measured.

[AManNamedNoah]

A new cast gear should be fine for a stocker especially with a 260 cam. As far as measuring the peak lift of the cam lobe, it's not square on the top, but ground with a slight slope to induce lifter rotation. Your initial measurements are typical of what I have measured.

Have you run engines with that type of wear on the cam? What has been your experience? I’d like to run my stock cam if possible but not if it’ll significantly affect performance/longevity.

[nirvairna]

Yes, I have run used cams with numbers similar to yours. What are the condition of your lifters, specifically the base of the lifter? If the base of the lifter is concave you might want to consider replacing the lifters. New lifters on a used cam will work fine, lots of people will say it won't but it does.

[66vairguy]

The Isky 260 is similar to the 140 stock cam, but has a little more lift. Fine with stock valve springs, but keep in mind those stock springs are only good to about 5,000RPM. Fine for a driver and easy on the cam.

Clark's 260 cam IS NOT AN ISKY CAM last time I asked. While I think highly of Clark's Corvair, their camshafts have had issues posted on forums (not sure who makes them). I get my 260 cam directly from Isky.

A billet cam gear is superior to the cast gear, especially aftermarket cast gears. I buy my billet cam gears from Calif. Corvair. Forget all the stories of "you can put a cam gear on yourself". I've heated cam gears in ovens and within minutes of removal from the oven they are too cool to install the cam. Jeff at Calif. Corvair has a fixture to keep the cam gear hot while inserting the cam. If the cam gear cools too quickly while inserting the cam it will broach the cam gear and lead to an early failure.

Considering the effort to install a cam when it fails I usually install a new Isky cam and new lifters. However - even brand new cams occasionally fail during break-in. If the original cam wear is not bad (and that takes an expert to determine) you can install new lifters and the risk of problems is low. If the engine was dirty and high mileage - I would install a new cam and lifters

Just my opinions

[bbodie52]

Before "Miking the cam" to measure its design characteristics and timing, Making the cam must be accomplished. This informative video will give you an idea of the process of designing and manufacturing a camshaft...

Click on the link below for more photographs and to read the detailed article...

https://www.dragzine.com/features/shop- ... t-is-made/

This is an amazing work of graphic art. After starting the video, click on the FULL SCREEN icon in the lower-right corner of the video to enlarge the image so that you can view all of the high resolution detail!


https://www.youtube.com/watch?v=sIBSeSHf_ks