racer rich

Hello. I have a question regarding engine head gaskets/shims. I would like to use 30% nitro fuel for my new XTM 24.7 nitro engine. In the instruction manual it states if you use 30% nitro fuel it is recommended to add a .10 mm head gasket/shim to lower the compression ratio. Now I have a 0.1 engine gasket/shim but it is for the Mugen MT12 engine. I don't think it is specially designed for it, but it says "for MT12" on the package so it arouses one question in me. Is there any such animal as ".12 engine only" head gasket/shims and ".21-above only head gasket/shims"? Are there specially designed engine shims for .12 engines and .21-above engines? If so, are they each of a different size (outside and inside diameter)? I honestly don't think so, but you never know. Here is a picture of the shims I will be using:



Do these look like the proper size engine head shims for this 24.7 engine (or I suppose a .21 size engine)? Engine head gasket/shims are very hard to find in my area (I actually mail-ordered those from Hong Kong!) so I hope these will work. I don't want to ruin my engine, so I will seek advice first before using them.

Finally, one last question. I will be breaking-in this engine in with 20% nitro fuel (recommended by XTM). Should I install the .10mm engine head/gasket shim prior to break-in (with 20% fuel) or after break-in and prior to using the 30% fuel? I am thinking that using the .10mm head gasket/shim during break-in while using 20% fuel might cause erratic engine behavior since the .10mm shim is meant for use with 30% fuel. Is this correct? If so, I suppose I would only want to install the shim right before I use 30% nitro fuel?

Sorry for all the questions! Your advice and help in this matter is greatly appreciated.

Thanks,

Rich

popsracer

Racer rich;

You will need to buy the EXACT Gasket/Shim for your engine. The Gasket/Shims are designed to fit a certain Sleeve and Cylinder Head combination and are not mix and match. Just order the correct ones from your XTM dealer. Also if your not RACING, there is really no need to run 30% Nitro in your engine. 20% should be just fine.

Jon Carlson

iTrader: (48)

to add to what pops said if you are not going to be using 20% then don't break in your engine with it. Use the fuel you are going to run while racing/driving to break the engine in as well. And don't worry if you were to run 20% instead of 30% you'd still have more than enough power. Have fun.

Jon

NitroJoe

POP,
I just wondering, Is it ok to run the engine w/out the Gasket/Shim?
thanks

Corse-R

Nope! unless you've a grasp on what you're doing. Removing head gaskets made some things on your car, let's see:

Removes head clearance (Dangerous, you can smack your piston to the head and do nasty things on your block).

This raises your compression up to unknown levels, blowing a head, breaking a conrod, piston or beating the crank are fine things that happen to your engine.

Done with some control you can achieve more HP, but keep on mind that you can start blowing plugs at a fast pace. I did it on small quantities to get some extra HP, but careful with it. Your piston/sleeve expected life shortens a lot.

NitroJoe

Thks for the infor. BTW do you have the infor where and how to mod the engine? I am just curious about how to mod the engine, to see what happen and also experiment the whole mod thing? Thanks again.

Corse-R

I have limited knowledge modifying engines (do some limited porting rather than extreme works made by Motorman or Smeltz), ever before engaging a dremel work on the engine I try to do some work on the exhaust.

Working on the exhaust if you run on ROAR races is simply to bore with a 5mm or 5.1mm your exhaust tip (many of those 'high performance' exhausts come to 4.8 or 4.9mm).

Try to rework your carb venturi (Novarrosi and others comes with 5.3mm venturis rather than 5.5mm).

For all bore work I have some chrome-cobalt drills (you'll notice them by their gold finish). Very hard and very sharp (the last you want is to ruin a carb or exhaust for a faulty drill).

For some dremel work on your engine, you may have to know a little what you want to get from your engine (be real: getting 2Hp from a 12CZ-R is a joke). Do little changes and subtle at time and try to notice what changed on your engine.

bbntc3

For 30% Nitro use I think you want piston to head button clearance around .018 thousandths.

BOLISARIO

iTrader: (57)

So, if you're running 30% on your new engine, will the shims that come with the engine be more than adequate? Or will I have to add a shim? With my old RB X12 turbo, I ran the engine "as is" for about 3 gallons and didn't notice any problems.

I guess what I'm really asking is when do you have to add or remove head shims?

bbntc3

I use RB X12 5port turbos, I just add a 0.1mm shim to the stock shim. You can probably get by with out any extra shims, Theres a post or 2 in the RB Forums I think about this. I think with RB's you want 0.4mm shim under the button, but not positive on that!

rccraze

i have a sts rs12 engine coming in the mail and i want to use 30% nitro since i dont want to buy more fuel. Can someone tell me the part number for the head shims set or some other head shims that i can use that will be usable in that engine. I need a reply soon because i have a little race coming soon and i still got to make a order at my lhs for it. Thanks Also got a sx12 non turbo that also need head shims