To drill or not to drill

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[XTRevolution]

If some of you remember, I had issues with a burned valve. I sourced a pair of heads from someone up in Wisconsin off the Bonneville forums for my L27. Turns out he sold me heads off of a 1992 engine, not a 1993, which makes all the difference. The rocker arm bolts for the 93-95 (what i have) are 5/16", and for the 92 and below, they're 3/8", which is 1/8" bigger.

So I have myself a problem. I've already spent the money on the heads and other random engine parts, so I need to get this done. Will I be safe drilling 1/8" larger into my roller rocker pivot mounts and the bases in order to use the 3/8" bolts? I'm under the impression that the heads are otherwise identical.

I posted this on the bonneville forum as they have more experience with the L27's in particular, but I figure I could get some input from you guys.

At this point, I don't think drilling 1/8" into the material will cause a failure point, as I'm only drilling into the rocker arm pivot mount, not the arm itself. Therefore, I'm not weakening the parts that experience the most stress. The pivot mount never moves. Here are some photos that should help.

Roller rocker with factory bolt:


Pivot mount I need to drill 1/8" larger (its that part in the middle):


Rocker base I also need to drill 1/8" larger. Comparison of 3/8" bolt and 5/16" bolt:


3/8" bolt on top of the rocker base:


Comparison of rocker, base, and both bolts:

[AWeb80]

you're only taking out .060" per side if you drill.   i'd say if you are careful when drilling, you'd be fine.  find someone with a mill and a vise if you can so the rocker is held snug when drilling.

[Chris]

I wouldn't do it IMO. Bring it to a machine shop.

[XTRevolution]

I wouldn't do it IMO. Bring it to a machine shop.

That's what I was planning on doing. I know I couldn't be precise and careful enough with hand tools. Just wanted to make sure the whole idea was alright.
Post Merge: March 30, 2010, 09:24:49 AMI have a machine shop doing the work for me now. They'll drill out the holes and put in solid inserts for the 5/16" bolts. The rockers can't be drilled through since the fulcrum is hardened steel. My other option was to contact yella terra for a different fulcrum size, but I doubt they're going to have anything for me since this is virtually the only performance modification supported for the Series 1 3800.