Mag 15 XLS Head Shims

Tell us what you do to get the best performance from your engines.

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sgilkey
Posts: 2351
Joined: Mon Mar 19, 2001 8:26 am

Mag 15 XLS Head Shims

Post by sgilkey »

Decided to play around a bit with my Mag 15XLS. Does anybody have a good technique for removing the head shims? With this engine, the shims sit in a counterbored ring-shaped cavity in the head. can't get at them from the side. my usual technique is to poke in from one of the head bolt holes but all those holes have a full wall adjacent to the shim cavity. To make matters worse, the shim material is soft and thin, and the OD appears to be at least the same as the shim cavity, if not slightly larger, so when the head is torqued, the shim kind of bends such that it locks itself in the cavity. Finally, even if it's reasonably loose when new, after a bit of running congealed fuel will lock the suckers in.

I tried picking them out, finally was able to blow them out with compressed air and a lot of bad language. Needless to say the compressed air (and my language) blew the shims across my garage and it took me 15 minutes to find them.

None of this seems reasonable for "field tweaks" on contest day!!! At this point I would never consider trying to remove a head shim other than under laboratory conditions!!!

Anybody come up with a good way to get these boogers out? I plan to try to remove the wall around one of the head bolt holes so I can go in that way, not sure it will work. Also I think I will trim the OD so they do not quite fill up the head cavity. I measure the OD of the cavity at about .008" (.004" on the radius) larger than the liner flange, so a bit of the shims could be trimmed off without affecting sealing. Tedious but maybe worth the trouble???
Scott Gilkey
RCCA# 330
montague
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Joined: Wed Feb 27, 2002 3:24 pm
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Re: Mag 15 XLS Head Shims

Post by montague »

You're not going to like my answer I suspect. But I've been using a T-pin to basically poke along the outside edge of the groove at an area where the shim has folded up along the edge as you describe. Once it's up a little, I can usually shake it out into my hand. Sometimes the shim dies in the process, but spares are cheap, so it's not the end of the world, even if it is annoying.
Kirk Montague Adams
RCCA 560
[url]http://www.MidAtlanticCombat.com[/url] - Combat in the Mid-Atlantic Region
sgilkey
Posts: 2351
Joined: Mon Mar 19, 2001 8:26 am

Re: Mag 15 XLS Head Shims

Post by sgilkey »

i removed all mine and carefully trimmed the OD. you've seen my planes so you know how much craftsmanship is indicated by my use of the word "carefully." at least now they can be removed (hopefully) more rapidly if i ever get the urge to make changes at the field, which is unlikely. i can't remember the last time i juggled head shims at the field, but then I haven't run the XLS in competition yet.
Scott Gilkey
RCCA# 330
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