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General Category >> Rubber Side Down! >> Head repair at the machine shop
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Message started by RycaShawn on 07/27/11 at 22:23:04

Title: Head repair at the machine shop
Post by RycaShawn on 07/27/11 at 22:23:04

Has anyone actually had their head repaired at a machine shop from excessive wear on the cam journals? I have been trying to repair my head using sand paper on a surface plate (precision ground stone plate) and a 20mm reamer (from MSC $58) and I still have to take a lot more material (0.005-0.006") out of the head just to get the clearance back to spec on the main 25mm journal.

I am curious how much the repair cost. My machine shop turned down the work because the cam is in a blind hole and not a through hole with plugs on either side. That makes it not possible to use the typical boring bars used to repair journals and line bores. Custom bushings and boring bars will need to be made or purchased. Anyway, I've decided to take this on myself. I guess I better put out for the $65 25mm reamer now. My only fear now is that the geometry of the rockers will have changed so much that the tappets may slip off the valves and lock open, but I will be sure to check em. Oh yeah and the cam chain is going to be a tad too long now as well....but we are only taking 0.010-0.020" excess length for the tensioner to take up.

Title: Re: Head repair at the machine shop
Post by verslagen1 on 07/27/11 at 23:17:30

I went thru the cam chain geometry awhile ago, and calculated the for every 0.01" of chain stretch you'd have 1° of cam retardation.

If you're dropping the cam in the head by .01 to .02, then you're retarding the timing by 1 to 2°.

I would think those journals would need to be concentric by less than a .001". I would buy the 25mm reamer and have it stepped down to 20mm

Title: Re: Head repair at the machine shop
Post by RycaShawn on 07/28/11 at 08:06:13

hmmm 2 degrees of retard. Sounds like I need to make the cam gear adjustable. Who knows what I need with this Web cam and 2mm overbore. I'm going to go ahead and confirm your calculation!

Title: Re: Head repair at the machine shop
Post by buttgoat1 on 07/28/11 at 09:49:41

advancing a cam is sposed to improve torque.
We would not notice a small drop in torque as the chain stretches since we have plenty.

Title: Re: Head repair at the machine shop
Post by Oldfeller on 07/28/11 at 19:50:39

http://suzukisavage.com/cgi-bin/YaBB.pl?num=1268452150

You cannot use two separate reamers to do the two separate surfaces as they will not line up when you are done (ask me how I know).

Read this and remember -- this was 8 months of effort (several different methods were mocked/attempted before settling on this)

It was the accumulation of several years worth of cam journal fixes by a number of people.

Line up of the pins is critical -- mark your pins so you put them back exactly as they came out. Correct end into the head, witness marks lined back up exactly ....

Keep your 20mm reamer, it will be useful.

Don't bother buying the 25mm unless you do like Verslagen said, get it precision stepped down to 20mm on a cylindrical wet grinder by a toolmaker.

Title: Re: Head repair at the machine shop
Post by RycaShawn on 07/28/11 at 21:31:34

I agree with the single tool approach, unfortunately I didn't start that way. I will be spending my entire Saturday all on set up and it won't be a 25mm reamer...boring bar. I know, still not as good as a stepped reamer.

Title: Re: Head repair at the machine shop
Post by RycaShawn on 07/30/11 at 20:23:29

Phase 1 complete. Cam cover mating surfaces decked flat and parallel to the deck surface. Only took 8 hours today. Only like cutting open a skull. The brain surgery is the tricky part. And now to think about phase 2 for a while before the attempt.

Pretty satisfied that my rocker arm pins are perfectly parallel to the newly machined surfaces.