[AJCoholic]

I have always been under the assumption that the larger, gas burning engines which use a walbro carb need to have a non-heat-conductive spacer block (generally nylon or bakelite) in order to prevent issues that can occur when the carburetor gets too hot (if in direct contact with the hot cylinder).

I have been reading many heli-specific threads, where everyone and everyone's brother seems to have issues with the stock G20 and G26 carb blocks leaking air (which is very odd, since I have never heard this complaint by the many aircraft flyers who use the engines stock.

There are a few companies making machined aluminum carb blocks for the G20 and G26... and most heli gas flyers are saying you "need" one of these. I think its snake oil... why would they be having so much problems with the stock ones? And why doesnt the fact its aluminum, and the heat will transfer very easily to the carb, cause issues? (from what I have read, it might)

AJC

[mogman]

I have had problems with the Horizon Hobby supplied G26 carb rotator block ( to get a direct throttle linkage). As soon as you put the slightest presure on the bolts, the block splits where the metal threaded insert is. I repaired one using zap, silicone sealer and a zap strap...still working ok.

My CRRC 45 has no insulator block. It has a metal manifold with just a gasket either side.
No running problems, a little hard to start when hot due to heat soak. A couple of flips with the choke on solves that problem.

Dave.

[AJCoholic]

Originally Posted by mogman

I have had problems with the Horizon Hobby supplied G26 carb rotator block ( to get a direct throttle linkage). As soon as you put the slightest presure on the bolts, the block splits where the metal threaded insert is. I repaired one using zap, silicone sealer and a zap strap...still working ok.

My CRRC 45 has no insulator block. It has a metal manifold with just a gasket either side.
No running problems, a little hard to start when hot due to heat soak. A couple of flips with the choke on solves that problem.

Dave.

But Dave, there are LOTS of airplane guys running Zenoah's - and how many times have you heard this was an issue? Yours in the first for me. I have had 5 myself, no issues. I know lots of guys running them, no issues.

I was just surprised that guys replace the carb block immediately, assuming there will be problems with them leaking...

If the insulating block wasnt required I question why 99% of engines have them? I am genuinely curious!

AJC

[guyl]

Carb Block Isolators are what it means. To isolate the walbro carb
from a direct mounting on the engine block. What it does???
It provides a cooler airflow charges into the cylinder....Cooler air
intake holds more oxygen for any given amount, therefore a larger
amount of fuel can be injected FOR MORE POWER.
An aluminum spacer (not an isolator) is certainly not the intention.
With a cowled in 50cc gassie; Is it something you will readily discern???
Guy

[Flypaper]

It's to stop vapour lock where, without it, the heat transfer will raise the temp in the carb high enough to boil the gas,or vaporize it if you will, shutting the motor off. Same as the fibre block under a car carb for the same reason.

[mogman]

Andrew.



To clarify, I have had NO problems with the insulator that comes with the Zenoah. It's the blocks from Horizon Hobby to turn the carb that cause me grief. I have had 2-G26 blocks split, along with 4-G45 and 2-G62. The aluminum blocks would certainly not be an insulator, but as I stated my CRRC 45 has only a thin gasket between the carb/steel manifold/engine with NO running issues other than hot starting.

Dave.

[Guest]

Andrew there are no problems with the stock carb block I have logged over 15 hours on a Radikal with a G20 in it, some have suggested using two gaskets on the intake, I just used the stock one and built the heli right,there are no issues.

[Tyler P]

Do gassers in helis run hotter than in planes? I would think that they might because of there being slightly less air being forced over the head to cool it. I could see where an isolator might help this as was mentioned earlier about vapor lock.

I have limited experience in gassers, having only had one for a year, but I suspect I might not be too far off in my assumption.

[vinver]

There is NOT a solid aluminum block here- there is a step machined in the engine-side of the block, and a thick (about .080", 2mm thick ) white teflon? gasket spacer between the aluminum block (Z-RC brand) and the engine.
Bergen RC highly recommends the Z-RC block, overtightening of the standard part can warp it and cause air leaks, leaning out the mix with obvious bad things happening...
Heli engines usually run flat out, with only about a 2 inch fan to cool them inside a fan shroud, as opposed to airplane engines with a foot and a half prop ,wide open to the airstream.
Ask Chris Bergen why they are a good idea.. www.bergenrc.com

Vince

[vinver]

http://helifreak.com/showthread.php?t=32213

I hope cross-posting from other forums isn't frowned upon by the New World (RCC) Order.
Vince