Brodak 40 head shims

My Dad has about 200 flights on his B-40 and it still had a small sag in the 2stroke as it goes over the top. Someone suggested adding a head shim. A Thunder Tiger GP 42 head shim is .016 and fits pretty nice. A few thou bigger ID than the stock .006 gasket.
He also twisted the ST NVA to line up the holes better and threw off the test. The draw was very good with one hole just showing.
Any way, the TT 42 shim fits if you cant find a Brodak shim. MM

The .010 shims Leonard offers for the OS40FP's are a perfect fit as well in the Brodak 40.
I have two B 40's. One is a horse, totally predictable, great guts in a 4 stroke mode. The second, from a later batch, the batch with rotated sleeves, funky threads, etc. has much less power, is somewhat tempramental, no guts in a 4 stroke. Various prop, fuel, tank and airplane combos have been tried. The above mentioned additional shim also seemed to have no effect at all based on casual observation.
The engine has since been returned to Brodak and, as usual, John has indicated he will get it right or replace with a new engine. Is this great service or what?

Interesting,

I am also running two Brodak 40's, one in my ARF Nobler and one in the Omnium. The one in the Omnium has the cylinder slightly out of alignment but I didn't notice it until I had a couple of gallons through it. I am afraid if I turn it now it will need to be broken in again and wear faster. They both run great but have to use different props. The one in the Nobler likes a Rev-Up 11-5 and the one in the Omnium likes the APC 10.5 x 4.5. I wished I understood enough to know what the difference is, all I know is if I put the Rev-Up on the Omnium it is wind-up city.

I picked up a couple of extra head shims while I was at Brodaks last summer but haven't found any reason to try adding any to either engine.

My Brodak 40 sags in power when it breaks into a "two" on cool damp days, but transitions nicely on hot dry days?? This is a puzzler as the engine is well broken in. Fuel 25 % oil half castor and half synthetic, 10 % nitro. Various props were tried and the best seems to be APC 10.5X4.5 .
Bigiron

Gentlemen: My Brodak 40 has had about 15 min bench time, following the instructions, and one flight in a JC Yates DRAGON. With this plane, the motor requires a flat-out 2-cycle. It runs well.

My concern is that the B-40 seems to have too much compression! %This is the only motor that I am afraid to hand-start without a chicken stick! It kicks like a mule!

Would I be better off to intstall some head shims (from OS40) to tame it down, or would this cause the HP to suffer?

I am used to the OS and Fox engines, where they don't kick back on starting.

Floyd aka: Dr. Spark

>Gentlemen: My Brodak 40 has had about 15 min bench time,
>following the instructions, and one flight in a JC Yates
>DRAGON. With this plane, the motor requires a flat-out
>2-cycle. It runs well.
>
>My concern is that the B-40 seems to have too much
>compression! %This is the only motor that I am afraid to
>hand-start without a chicken stick! It kicks like a mule!
>
>Would I be better off to intstall some head shims (from
>OS40) to tame it down, or would this cause the HP to suffer?
>
>I am used to the OS and Fox engines, where they don't kick
>back on starting.
>
>Floyd aka: Dr. Spark

You want to set the comnpression for how it runs, not how it starts. The compression is from the tight fit, undoubtedly. Just back flip it if you don't like it. You should be able to work up a routine where your finger isn't even in the eay.

I am going to assume that the compression is set at a certain level for a purpose. If you are going to change that compression level, do it for a purpose. Just to add a shim or two (especially a 16 thousandth shim) because it feels like a lot of compression will serve only to kill off the power. It will 4-2 alright, but it won't pick up any steam in 2-cycle mode.

>It will 4-2 alright, but it won't pick up any
>steam in 2-cycle mode.

Interesting observation, could it be that some stock Brodak 40's are low on compression generating the reports that some engines lose power when they break into a 2 cycle?

Ithink that the theory is, that they are a tad too high. When they go into a 2 they pull uitill the heat comes up and then the compression builds enough heat to start igniting too early, hence the sag under load. We fly at sea level and often have to add shims in relation to prop size and rpm. Sometimes a 36X will pick up 20mph with one more shim.
Dads' B40 is on a Twister with 10/22 fuel and 11x4.5 prop
MM

Maybe we should trace down these reports. First off, remember that John will stand by his product, so if there is a problem I would check back with John. He is as anxious to make sure all is well as anyone (probably more so). And he will stand by his product. (I just wanted to emphasize that.)

But maybe I have been sleeping or something, because this is the first time I have heard of this. There was one batch where it was reported that some of the sleeves were turned. None of the ones I got were off, however. So maybe it was one worker who was assembling them. Or maybe he (she?) had a bad hair day and it threw him (her) off.

I am wondering, hypothetically, if it is possible that a sleeve was put in backwards? And it doesn't have to be from the factory. Sometimes we modelers take these things apart, goof them up, and then when it doesn't work we blame the manufacturer. I have had some wierd combinations of engines sent to me.

That said, I have only disassembled and measured one Brodak engine. It would be interesting to measure a series of engines just to see what tolerances come through. But I have measured as much as 17 thousandths difference in deck height in OS FP engines that were stock from the factory. That is more than one head shim difference. I should note, also, that this difference is almost 100% guaranteed to be in the direction of low compression. Oh, and those tolerances will be found in LA engines, also. Just because one person reportedly runs his engine "box stock" or "adds one head gasket" doesn't mean yours will run the same way.

There will be some tolerance differences in any engine. I would hope that the Brodak engines are a lot closer to specs than that, but, yes, it is possible that one could have slipped through that was off that much. And deck height is one of the first things I correct on any engine I rework (or at least make sure I can before doing anything else).

Maybe we should ask, Has anyone experienced that problem? If so, what prop, fuel, etc. were you using? (Maybe we should start a new thread. And, again, this is not to knock these engines. John will stand by them if there are any problems at all.)

my B40 sags when it breaks into a two cycle also. Tom Hampshire suggested a head shim to lower the compression to reduce the effect. he said some of them come through with a bit too much compression. Haven't tried it yet since the plane flys fine in a solid four cycle.

>my B40 sags when it breaks into a two cycle also. Tom
>Hampshire suggested a head shim to lower the compression to
>reduce the effect. he said some of them come through with a
>bit too much compression. Haven't tried it yet since the
>plane flys fine in a solid four cycle.

If you pull the head, could you measure the deck height on the engine? You will need to use a caliper or similar "gadget". Rotate the piston to the very top, making sure the sleeve does not move (I like to push the piston up before removing the head, but one still needs to be careful.) Then measure from the top of the piston to the top of the sleeve. I would be curious to see how much, if any, variation you have there. I am going to assume that the head shape and gaskets supplied are stock.

This could also be a factor of setting the engine too lean, using too much nitro (need lower compression with more nitro) too small a venturi, too big a prop, too much restriction with the muffler, among other things.

Gentlemen: I guess the message to me is "don't mess with the B-40". Mine has plenty of power, but I'm running it at a slightly rich 2-cycle. My concern was about the apparent high C/R which forces me to use a "chicken sick" for starting. (yes, some of my OS engines can be started with a "back flip". I haven't tried this wih he B-40).

Perhaps my B-40 will become user-friendly with a bit more running.

Floyd. aka: Dr. Spark

I have four B-40's and will see if I can't get around to pulling the heads and checking them over the weekend. Two will be easy the other two are in airplanes but I think I can get the heads off without any major disassembly, should be interesting.