telmore

Whatever I try....

Does this backplate wear look excessive to you?

Annette

init4fun

Yes , that is one sad lookin backplate ...

If it has no or low compression , it's a likely result of all that missing metal grinding the piston/liner fit all to heck ....

telmore

Thanks for the response.

Piston and liner and comp seem fine.

But I have pulled the engine apart but could not get the conrod big end off the crankpin.

It seems likely the crankshaft and/or bearings are not seated properly.

How about a thicker backplate gasket which may allow the engine to run and the bearing to seat properly?

Gannett's

Broken Wings

My Feedback: (20)

I don't own a Thunder Tiger .15 but I believe they are "plain bearing" engines.

If the engine is a "plain bearing" or "bushed crankshaft" no ball bearings....there should be a thin washer behind the propeller drive hub. If this washer is missing it will allow the crank shaft to contact the back plate. It looks to me like the washer/spacer may be missing.

RCPAUL

My Feedback: (1)

+1

telmore

Here are some pics of the complete unassembled engine.


I have now got the piston out.


The washer behind the prop driver is there.


What would be the best bet - to clean up the backplate with some emery cloth taped to something flat - or to fit a thicker gasket - or both?


I think I've been lucky as there seems no other damage.


Annette

jeffie8696

What fuel?

telmore

20% castor, 10% nitro

jeffie8696

That should be perfect. I would just go back to the basics, glow driver good and hot, proper prime, etc. I have run in to engines that do not like electric starters, you may want to try just manually starting this one. From the looks of the backplate this one may just be one of those.

telmore

90% of my attempts at starting were by hand including the first.

AFAIK this engine had no appreciable running when I bought it.

Mr Cox

Ooops, looks like someone has been grinding away with an electric starter on it...

You need to check how much the crankshaft can move back and forth with the backplate on, you can leave the cylinder etc. off for this test.

Here are two images of the same motor, first when the crank is pull out as much as possible and the second when the crankshaft is pushed in as much as possible (and crankpin hits the backplate).

The washer will (or should) rest against the small ridge on the crankshaft, and as visible in the second picture this ridge should have to pass the front bearing surface before the crank pin hits the backplate. If you don't have a washer it still works as the propdriver will also rest against the same ridge.

I can't actually see any washer in your pictures above, I can only see a washer for the prop nut.
My engine didn't have any washer either but you will need at least a thin brass washer there if you want to use an electric starter, you cannot let aluminum grind onto aluminum in the front.

Mr Cox

As for the starting problems I would check the carb retaining bolts, they can easily strip the plastic carb and they you get major airleaks there. Try an 8x4 prop and 5-10% nitro, plus 20-25% all castor. If the engine has compression, a good glowplug and some fuel it will always fire...

ffkiwi

I dare say an OS washer for a 10/15/20 will fit-you can get these as an individual spare, if a proper TT one proves elusive..... [dependinging in the measurements of the shaft and crankcase nose diameters] As an alternative-and requiring the same data-modelfixings.co.uk do a nice line in shim washers, in sizes from 0.1mm thickness up. Somewhere in their range you should find something suitable...and they're in your neck of the woods, so to speak....

ChrisM
'ffkiwi'

Mr Cox

It is quite easy to just make a thin shim from thin brass sheet metal, in order to avoid aluminium rubbing against aluminium. I have one mine for that reason, do a rough cut first then use a dremmel for the center hole and a pair of scissors for the outline...

ffkiwi

I'd rather use a lathe and do it properly without worrying about burring-and the lathe gives you the ability to do whatever custom thickness is appropriate for the engine....

Mr Cox

Yes of course a lathe is the best tool, but not everyone has the access or the ability to use one. I only have a hobby lathe myself, but it is good enough for making smaller things in soft metal.

Starting from sheet metal, one can however make these things without a lathe. Deburring is made on a piece of emery cloth on a flat surface (e.g. glass).

aspeed

Or a paper punch and scissors if it is thin enough. I use a protractor with a knife on the one point for thin head shims too. Sometimes a glow plug washer will work, depending on the size needed. It is usually easier to start a motor upright if that pic is what you are using. The fuel tends to drip out of the carb and doesn't get wet enough. Or start it with the plane upside down. I never had much luck with the smaller TT motors myself, but they usually do work to some extent.

Mr Cox

Just to clarify, I took the front end my engine apart and photographed it upside down in order to help the original poster...

The engine runs fine, the one issue that I've had is that the carb retaining screws will come out so that is something to check for the OP.

The engine gives around 13500rpm on an 8x4 prop and around 15000rpm on a 7x5 prop. The low end is very rich, even with the airbleed fully out, so it might work better with an idle bar plug (I haven't tried that on this particular engine yet though).

telmore

I've had a tankful through it now!

With an extra gasket at the back and an OS carb instead of the plastic one.

Looks hopeful!

Needle was open nearly 7 turns...

Annette
Annette

aspeed

Mr. Cox, sorry I thought it was the OP pics. 15,000 rpm is good, better than my newer style one. Glad to hear it is working for Annette.

flyer7007

My Feedback: (20)

Hello all I have been reading this thread and very rarely have anything to say. I have been flying R.C for about 45 years. and have a lot of experience with these small temperamental engines. After seeing the back plate all that metal went some where and you will find out when you think it is fixed. I personally ,and this is just my opinion and am not saying anyone is wrong or has given bad advise. I would take the motor, clean it up and put it on my desk as a paper weight. buy a new OS 15LA and go fly. have a great day.

Mr Cox

Yes, one could even use an electric contraption instead of an engine, but where is the fun in that?

It is a hobby after all and running the engines is a major part of the fun, as I see it. There is nothing temperamental about these engines, they just need the correct fuel and prop and then they run as good as any of the larger ones. Plus a well treated lapped engine will easily outlast the fragile nickel coating that OS uses, but that's another story...

downunder

Those shavings probably aren't going to cause too many problems (if any) because it obviously uses a cast iron piston in a steel liner and there's no ball races to worry about. What intrigues me though is the pattern of that backplate scoring. I can't quite figure out how a flat ended crankpin could cause those ridged scores.

khalif

If everything was cleaned properly there should be no problems, the scoring on the backplate is strange. I don't think an extra gasket on the back plate is a good idea, this will reduce crankcase compression. The endplay in the crankshaft should be reduced to a few thou with washers/shims and then it should be checked that there is no contact between the crankpin and the backplate.
I have several TT15s and the 7 turns on the needle is also strange, both of mine are around 3 turns and the idle adjustment was OK. I just noticed it was not an original carb, I had probs with the carb on one but a new set of seals sorted it. Original carbs are about $25.

74SEVEN7

In the photo showing the cylinder liner, I'm curious as to what that hole is, just beneath one of the cut ports ?