SUPERFORMIAN

Greetings R/CTech users. Many of us know Losi makes engines with button heads for standard plugs, and they also make turbo head conversions for those engines. I know the obvious reason for why those would work together flawlessly, but what about a turbo head not made by Losi as an example? Anyway, let's get to the problem. I have an HPI Trophy 3.5 with the NitroStar F3.5 engine. We all know the 2011 model is waterproof, right? So, I was spraying the NitroStar engine while it was running with a hose and to my dismay (by way of science) the button head softened a bit from the combination of the cold water and heat from the combustion chamber underneath. The result? I attempted to remove the glow plug from the button head and the threads in the button head stripped. Most would go and purchase a new boring standard plug button head. Not me. Instead, I purchased an O.S. 21VZ-B V-SPEC II turbo button head thinking of the possibility to convert it to a turbo plug engine. As many of us nitro users know, the button head has been drilled specifically for the engine it was made for. For example, drilled for the specific timing of the nitro engine. That didn't stop me. A tight fit for the button head, but it worked. Checked the O.S. turbo plug for a bright glow, installed it, primed the engine, and attempted to start it. Surprisingly, there was detonation! However, no real ignition. Now, we all know detonation is exactly what we don't want. Knowing this button head wasn't made for the NitroStar, detonation is impressive!

So this is what I'm wondering; is it really possible to use a turbo button head from a different manufacturer? Or does the turbo head need to be drilled from the exact specifications as the standard head, just with space for the turbo plug?

I may have answered my own question, but knowledge from the rest of the community would be very helpful.

Jaz240

iTrader: (52)

I'm no engine expert but I think you may be able to get it to work if you shim the button properly. What the shimming should be I have no clue.

SUPERFORMIAN

I may have tried that, but it's worth it to try again. Less shims, higher compression (and possibly the risk of the piston making contact with the button head). More shims, less compression (minus that risk). Should I try more compression or less?

Roelof

At the end the volume is important. The volume is determing the compression and with that the ignition timing.
With a small injection needle you can fill up both combusion chambers with some fuel (with plug installed) and see the difference read out on the scaling of the injection needle. Normally it should not differ much. And while using a different button head you should use the solder trick to determ the real head clearance.

Jaz240

iTrader: (52)

I would try more shims first. You can't hurt your engine like that. Add 1 thin shim at a time and see if you can get it to run.

SUPERFORMIAN

The NitroStar already includes 3 shims. Should I remove all the shims and add one at a time?

SUPERFORMIAN

When you say injection needle, do you mean tuning the carburetor? This "solder trick" is something I haven't heard of. What is it?

Jaz240

iTrader: (52)

I'm not sure and don't want to give you mis-information. I do know that adding more shims will not hurt your engine, but lowering the button will if it's to low. If you have extra shims try adding 1 at a time to see if it runs. If it does not run then start removing them 1 at a time and keep trying. You will hear it immediately if it's not right but you very well may ruin your engine if the piston hits the button. You should wait for advice from someone who has more knowledge about this kind of thing.

Roelof

Take the combustion chamber, put a plug in it place it on an holder so it will stay straight, fill the needle with some fuel or afterrun oil and fil the combustion chamber until the edge. Look on scale of the needle what is used and compare.

The solder trick:

Get a piece of solder 1mm thick, bend the endtip into an L shape. Put it through the plughole and turn the crankshaft arround (with a mounted flywheel). Th solder will be squeezed between buttonhead and piston. Take out the solder and messure the flat spot on the solder. That must be arround 0.5~0.7mm but with the headclearance of the old head and the difference of the volumes of the combustion chamber you can calculate what the headclearance must be with the new head.