Hello,
My Magnum Pro 45 suddenly became very hard to start.
During last month, it always started after priming with the first flip and the launch RPM were 8,800-9,000 with 11x7 two blade wooden prop.
Now, I have to work hard to get it running and the static ground RPM are very low ( 6,500 max on the same prop.)

Checked the plug - it is fine.
Checked the fuel tank, fuel lines, fuel filter for some junk - none found
Checked the Venturi and the NVA - nothing suspicious found
Disassembled the engine completely and inspected everything - no internal damage found, all gaskets intact and in place but compression is weak.

The engine was "soft" during the last month but, again, it always started with a single flip. Perhaps the cylinder-piston "soft" fit became too loose a week ago?

I have removed the head gasket to increase the compression and got some of it back when the prop is flipped fast but the engine is not holding the air in the combustion chamber when the prop is slowly turned left and right, with the piston passing through the TDC.

How to increase the compression?

I have read the discussion about tapping the piston top to spread it but I do not think I will risk doing this.

Has anybody ever tried to machine the groove in the piston and use the matching steel ring in worn ABC engine?

Thanks,
M

The only fully reliable way I know to "check" a plug is to swap in a brand new one from a reliable manufacturer.  Just getting a glow doesn't mean that you've got a working plug.

if it is a Magnum Pro 45 with a two piece case, it is a clone of the OS 45 FSR, and  was made by thunder tiger, there are still piston sleeves around
try to find one or a  used engine  that have good piston sleeve fits are cheap finds at swap meets  and Ebay, or keep a watch out for one on the forums

Randy

There's not enough metal in the piston to cut it for a ring. Send the Piston and sleeve to RayAracing and tell him medium pinch.


MM

     Hi Chris:

     You are correct about the maximum size that Ray can shrink.  He told be that one inch was the maximum size that he could shrink.  I was hoping that he could shrink my McCoy .35 engines but due to their finned cylinder sleeves, the diameter was too large.

                                                                                           Be well,
                               
                                                                                           Frank McCune

Is that the second time you've had it apart, Matt? Just wondering. It's hard to believe it won't even start due to low compression. Low power, yes.

I've got some good FSR parts at the house. I'll look and see if I have a piston/liner.

See the attachment.
Will these fit?
No response from the sellers yet.

See the attachment.
Will these fit?
No response from the sellers yet.

It's much more likely that a Thunder Tiger .46 piston/cylinder would fit...made by the same company. I have a TT .46 that was given to me in parts. The piston/cylinder looks to be good. Have you got a mailbox on this side of the border? Free plus postage.  Steve

You're looking at a lot of work for that engine, Matt. Have you considered just buying another? Here's one on the RC forum:
http://www.rcgroups.com/forums/showthread.php?t=2313188&highlight=Magnum+Pro+45

I checked my parts but only have a 40 piston/liner.

The engine is running great and the compression somewhat improved!

I am flying tomorrow.

M

Steve,
All the screws in this engine are socket head and yes, I tightened the engine head screws in a diagonal pattern, using very small Allen key moves.
When the engine was completely disassembled for the second time, I inspected all mating surfaces of all the parts with a very strong magnifying glass ( 10X) an found nothing suspicious.

Remembering my Jett 60 dying in the air because of rust that got loose and damaged the piston, I paid particular attention to the piston of this Magnum. I have cleaned it with acetone, dried and used the concentrated light beam at angle to see possible scratches and dents. Of course I found some but they were the order of magnitude smaller than grooves dug in my Jett 60 piston by the rust particles.

Oiled cold Magnum piston moves freely in cold Magnum liner to the level 0.15" below the liner top rim and than the resistance quickly grows.

In my opinion, this indicates softer but still adequate ABC fit.

Magnum Pro 45 has two crankcase gaskets. One in front of the short, main crankcase block, one at the rear of the same block. Both gaskets were intact though heavily soaked in oil. After some more scrutiny, I have decided to replace the front one with the gasket cut from the beer can. I have sanded the paint from this aluminum sheet with 400 sand paper, cut the gasket and tried it tightening the four mounting screws of the front part of the engine in a diagonal pattern. Then, I removed the front part of the engine and inspected the gasket finding the regular and continuous imprint. Then, I put the front part of the engine in place and tightened its four mounting screws in a diagonal pattern.

The original Magnum glow plug ( with idle bar) received new copper gasket and I put back the aluminum engine head gasket I have removed after first disassembly. This gasket was in good shape: no holes, no scratches and no folds.

When I put the engine together, oiled it and flip the prop, the compression seemed to improve somewhat. I believe now that removing the head gasket during first disassembly was a bad idea, leading to a minute leak between the engine head and cylinder, weakening already weak compression.

After final assembly, I installed the engine in my Toucan ( formerly known as SIG Fazer) and tried to start it, using Omega 10-12% nitro fuel without extra castor added. and 11.5x7 wooden two blade prop. I kept priming and flipping the prop with no sign of life from the engine for at least three minutes, checking the battery in my glow plug from time to time and turning the needle one way or the other. THERE WERE NO BURPS. Suddenly, the engine started and run for about 15 seconds with the glow plug starter attached. When I removed the starter, the engine stopped.

I have removed the glow plug and check it. It gave strong, bright orange glow. Put it back and kept priming and flipping. This time I heard a little burp from time to time. Removed the glow plug again and injected some fuel into the combustion chamber. Put the glow plug back and the engine started for about 5 seconds.

After more priming ( the fuel was leaking from venturi) and from the tongue muffler, I have replaced the starter battery for the fresh one ( no load voltage > 1.4 V) and the engine started. It run for roughly 40-45 seconds without the starter attached but the RPM were low (~ 6,000 ) and the engine was lacking power. I have tried to slowly turn the needle to lean it and the engine died.

I have removed the engine from the plane and mounted it on my bench. This time the cylinder was up and I used the plastic 8 oz. tank with the clunk.

The story repeated itself: endless flipping, priming to the brim, removing the plug, checking the plug, putting back the plug e.t.c. I was getting little burps from time to time and got one short, weak run without starter attached.

Then, I removed the plug for the n-th time and kept mindlessly turning the prop "not thinking yet not dreaming" ( from "Enter The Dragon" with Bruce Lee). The engine completely flooded with fuel that was even leaking from the glow plug hole. " I flooded the engine" I thought lazily ready to use my long wood chopping axe
and smash this cursed thing to splinters.

Then I woke up from my "not thinking yet not dreaming" state, put the glow plug back and kept flipping without starter to get rid of all this fuel that was splashing from every engine opening.

It lasted for a while but there was no hydro lock.

Then, I attached fresh battery equipped starter and kept flipping. Again, only a single burp from time to time. I looked at the axe and hesitated.

"One last time" I thought "this time with another prop".

11x6 APC was installed and the engine started with the first flip. RPM went instantly to 10,400 and stayed like that. I turned the needle to get 9,200 RPM, just below 4 stroke, and the engine worked happily for 3 minutes.

I changed the prop to 11x7 APC, waited for the engine to cool down, fueled and started it with the first flip again, getting 6 minutes of stable run at 9,200 RPM.

I would not be able to fly today and tomorrow because it is "raining cats and dogs" in Toronto but I believe the problem has been accidentally solved.

Perhaps flooding the engine with fresh fuel helped to clean some residue of spirit, acetone and after the run oil?

The APC prop is heavier than the wooden one and has more rotational inertia. Perhaps this helped increasing the rate of compression change and the mixture properly ignited?

Regards,
M