BLOODforBLOOD-RCU

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Hey i was wondering if anyone would know anything about the thunder tiger pro 70bx engine?I have 2 ek4 trucks i was gonna get going but noticed neither of them have a head shim.One has the msj head the other i believe is stock .I can't find any info on the shim thickness so i can't even make one.Do i need a shim?I'm not sure but i think when switching to the msj head it said you didn't need the shim but its been so long i don't remember.If anyone could help it would be greatly appreciated...thanks

1QwkSport2.5r

I responded to your post on RCG as well, but I’ll add the same here. Your engine may not have used a head shim from the factory, though that’s not very common. Most often there is a shim present, but the shim is made of aluminum and blends in with the head button. A small pick can loosen it up to measure it. A shim is not needed for the engine to run unless the piston deck height is too tight. Check the head to make sure there isn’t a shim hiding on it. Then measure the head depth and piston to deck height and subtract the two. This gives you the uncompressed head spacing. You need at least .015” head spacing. If you have more head spacing (squish clearance) than .015”, you can lower the head for more performance, but you would need to make your own head shim from K&S brass or aluminum shim stock. I regularly make my own shims as the factor shims are often too thick to get to an ideal spacing.

Your engine is a converted airplane engine, which are often massively over-shimmed. This is a big safety net for running gobs of nitro in the fuel, but it basically neuters the engine and reduces its power capability. The average modeler won’t notice this though.

BLOODforBLOOD-RCU

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Thanks for for the help.I ended up solving the problem.It turns out there was a shim,it was just stuck on there,lol.I feel dumb to have to admit that but at least its there.I;m not sure how accurate my caliper is but its a .003 shim.Thanks