Thunder Tiger 70 4 stroke

[Mike Wright]

Has anyone flown any of these engines out there? They must be pretty new but I am surprised that the modelling press seems to have ignored it unless I have missed something.

[YakMad]

Mike,



I have an ASP 180 in an Extreme Flight Yak 74 inch wingspan turning an 18x6 prop, it's not yet fully broken in but it's certainly well able to pull this model around mostly at half throttle as full power is only needed for the vertical. I'am in the process of fitting a Pro-Build soft mount to the model as the vibration level is fairly high and the fuel is foaming in the tank causing lean runs. It also seems to be fairly easy on the fuel and it only require 5% nitro unlike most other large four-strokes.

[Robert Hunkin]

I wonder if anyone has had similar experience to mine with ASP 4 strokes?
The larger ones seem to be fine after careful running in but the 30 and 52's seem to suffer from poor quality control and inconsistent tolerances.

My 52 four stroke ran well until a lean run cracked the exhaust valve seat bronze insert. The new replacement head and valves have always leaked compression giving poor performance. [Has anyone discovered a way to seat leaking valves?]

My first 30AR ran well [10,400 rpm on a 10X6] but the exhaust header was machined too deeply and had a pinhole which leaked fuel. Nevertheless I bought another 30 to pair up in a Top Flite DC3.
Engine no 2, despite extensive running, struggled to make 9,200 rpm on the same prop and fuel, smoked heavily and was unreliable. Not good enough for a twin..

The local hobby shop then made me an offer I should have refused! They sold me 2 more new 30ARs at a 'bargain' price.

Engine no. 3 would not turn over and proved to have the cam shaft timing set 2 teeth out, causing the valves to hit the piston. Easily fixed, but more seriously when I ran the engine the front bearing came loose in the crankcase and had to be refitted with loctite. This engine did 9,600 rpm.
Engine no 4 had a carb with would not close as the slot in the carb barrel was inaccurately machined. With a new barrel it made a promising 10,000 rpm but would not idle reliably.

Determined to fly my DC3, I scratched identification on the main bits of engines 2,3 and 4 and started a long round of mix and matching piston sets, heads, carbs, etc and bench and flight testing. Finally, I built a 'bitza' that was reasonably matched to the incomparable Engine no.1
Even so when the weather gets hot, the bitza engine is too unreliable to risk in flight.

All the engines suffer from screws, idle needles, etc dropping out in flight. Needle valves are so wobbly that just touching them can cause the engine to
stop and on some carbs idle mixture screw adjustment has little or no effect.

My ASP 90AR is pretty good, I suspect because the machining inaccuracies are less detrimental with a larger engine and also because I've not tried to match it with another engine. However, after many hours running it needed a decoke so I took the head off. The cylinder had alarming vertical stripes, which at first I thought was scoring from grit ingestion or piston seizure. Under a magnifying glass I could see that they were areas where the machining marks were still visible. Could this have been caused by boring with a worn tool bit?

I now read the usually glowing reports of tests of ASP / SC / etc, four strokes in magazines; ['massive con rods, high quality castings, will last for ever' etc] with some scepticism.

Have I just been incredibly unlucky or do you get what you pay for? Are the smaller engines the worst? I would be interested in other peoples' long-term experience with Chinese clone 4 strokes.

Bob Hunkin [saving up for 2 OS FS30's!]

[001]

A new Thunder Tiger 54, started making a scraping noise after the first few minutes running. Found that the camshaft had been assembled dry and the lobes were worn, later it dropped a valve due to a valve clip breaking,it was always difficult to start and tune and frequently threw props.. Then to a new ASP 80,the first one was so badly made it had no seal at all between the head and barrel,its replacement had rapid excessive wear to the valve gear.But it did run quite well. After about 80 flights the crankshaft broke just behind the helical gear.
New Thunder Tiger 91, found that camshaft had been assembled dry, again, so lubricated it before use. (No I didn't mis-time the camshaft on either engine). Never could get it to run. properly.
I currently use Enya, O.S.(2) and Saito 4 strokes and have never had a moments problem with these in hundreds of flights (since 1987).
(No doubt there will be contradictions), but I will not touch these clone motors.
Buy cheap, buy twice.

[GrumpyGnome]

Just got a 'bargain' TT54 myself ............. gulp !

OTOH, I have an ASP 61 FS that's been great.

GG