Hi Matt. I spoke with Massive regarding the break in shim in the MG66, and he said not to bother with it. The new range of motors (MG66 and GX Series) are designed with less initial pinch, so the strain on the rod etc is greatly reduced. The 66 turned over on the starter box no problems without the break in shim, so the GX should be the same.
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Shane "Grizzly" Adams.
X-Ray XB 808 Buggy
GO MG66 & GO Stage5 5 Port / 2072 Pipe
MASSIVE MODS - High Performance Engines & Fuels.
ACE - AVID - VP PRO - SPEKTRUM
Grizz I just scored a rb modded 3 port with 1/2 gallon on it. Paid 90.00 for it. It is not run in yet. actually I took the back cover off to see the signature,sure enough it's there.Then I added the run in shim. One of the reasons I was asking about the new gx 5 port for the run in shim is because it is my opinion people want to run 4-5 tanks through the engines and start race tune. We who have experience with the go line know that is far from the case. And I believe that's why I got this engine for next to nothing.[besides people cannot read or comprehend on how to tune] My 5 port now has 3/4 of a gallon through it and is still tight. And like you I preheat every time until they are broken in. In the morning I will go through the seals and seal everything up. I wanted to get a new gx series 5 port but think I will wait until they have been out for awhile to see what every one thinks of them. If I hadn't gotten my traffic ticket I would own a mg 66. But looking back on my experience I am not sure I need or can handle all that power. I have a 7 port with 12 gallons on it.So I think I will wait till these other 3 wear out. See what the real deal is with the new line and then go from there. See what happens with 22 racer as far as buying an engine from him. Getting the engines, parts, what not. I try to take good care of my stuff so looks like I found my xmas present for this year.