ARP Bolt to cam shaft clearance - Hap please respond

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MGB & GT Forum: ARP Bolt to cam shaft clearance - Hap please respond
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Feb 16, 2009 11:07:46
pmittler

Hap posted this link and now that I am considering putting my stand-by engine into Gee Tee I decided to check the clearances he was referring to in that post.
http://www.mgexperience.net/phorum/read.php?1,1007079

Attached are photos of the bolts, taken through a mechanic's mirror and showing that these bolts have a camfer on them all the way around. If I position piston #1 at the closest position to the cam shaft I can get a .015 feeler gauge into the space but not a 0.16.

I have used these bolts and this cam shaft [Crane mild street cam] on a previous build without adding any additional camfer and I *think* the clearances are sufficient. I am reluctant to pull the caps to do this modification if it is not really necessary.

Comments?

Feb 16, 2009 17:05:50
JimmyHilton

Seems that I remember from Harry Singleton (Rufus) reflecting that there should be a .060" clearance there, for comfort. I can't really picture either the crank, rods, or cam flexing enough go that far, though.





Feb 16, 2009 18:06:02
Rufus

You guys are right. Hap knows this deal 1st hand, and posted photos and "how to" a few weeks ago.
Jimmy, your memory is too good. The 60 thou number came from the machinist that I'm using here in Beautiful Downtown Richmond Virginia. He agreed that chamfering the rod bolts was a good idea, he agreed that the folks at ARP should do that before they charge the outrageous price for new rod bolts, and he agreed that if it cleared 60 thou, it should be plenty for any sort of spirited over-revving I might do (miss a gear and go to 10). The 60 thou is an arbitrary number, "about the thickness of a wire coat hanger".
I'm supposed to get my pieces back from him this week, as soon as he finishes balancing the bottom end and matching the pistons/rods. I'll prolly do the build in a coupla weeks, and I'll report to the group as soon as I know.
In the meantime,
ASK HAP!!!
He really does know his stuff, its kinda what he does for a living.
Oh and by the way,
Have fun

Feb 17, 2009 04:13:22
Speedracer

Yes, a more aggressive chamfer should be done like the one I posted in the earlier thread, Peter, I wouldn't feel comfortable with .015", when everything is a full song you have grwth with heat and flex. The main problem here is ARP use a AMC V8 rod bolt for our application, which doesn't have the chamfer, and requires you to do it, I know it dumb, David Anton has threaten to bonk the ARP guys on the head for his dumbass oversight, but we've all beewn dealing with it now for 20-30 years, but it does catch out the new guys from time to time. Peter, I know you don't want to hear this, but pull the rods back out and do this, otherwise you'll probably have a rod bolt smacking the camshaft, look at it this way, better safe than sorry, I been in this boat a thousand times, many time I have pulled something back apart during assembly to look at something, many times there was no issue, but the peace of mind it gave me was well worth it.

The .060" clearence Harry refers to is a rule of thumb on moving parts and good guideline to follow.

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