Ofna Force .28 nitro engine keeps breaking the crankpin
11-11-2014, 08:57 AM
#1
Thread Starter
Ofna Force .28 nitro engine keeps breaking the crankpin
In the almost 1 year that I have had this engine it has suffered 2 broken crank pins which have broken off right at the joint of the pin and the crank web. The pin has a through hole which extends part way into the crank web to allow for the steel rod and spring that works with the recoil start assembly. I have stopped using the recoil start and have replaced the engine back plate and now use a starter box. When the last crank pin broke it caused the rod to burst the crankcase and I am concerned that it might happen again. Is there anything that can be done to the pin to make it stronger like possibly pressing in a steel dowel to strengthen the joint area.
11-12-2014, 07:54 AM
#2
I haven't heard of too many problems with the Force engines. To have a crankpin snap off takes a lot of force. Is the engine still really tight? You may need to warm the engine up a bit if it's tight and ensure its not sloppy rich so it heats up quick when running. Being that car engines are only loaded down when throttling them driving the car, they don't heat up as quickly as aircraft engines do.
Do do you have any photos of the damage?
Do do you have any photos of the damage?
11-12-2014, 03:55 PM
#4
Senior Member
Join Date: Oct 2006
Location: Sonoma,
CA
Posts: 1,289
Likes: 0
Received 0 Likes
on
0 Posts
running lean and/or a substandard fuel with a poor oil package can cause problems.
What brand of fuel are you using?
What brand of fuel are you using?
Last edited by nitroexpress; 11-13-2014 at 03:38 PM.
11-13-2014, 06:21 PM
#6
Looks like some rust pitting on the crankpin, but it's hard to say what really caused the failure. I doubt the fuel is to blame as there doesn't appear to be any galling on the crankpin. Lube doesn't look to be a problem. I have a feeling the failure is due at least in part due to heat (or lack of it perhaps). How much runtime did the engine have prior to the failure?
11-14-2014, 08:27 AM
#8
Thread Starter
Those rust marks have only appeared since the engine was dismantled about a month ago as previously the pin had no marks of any kind on it. The engine is in an Ofna LX2 1/8 scale buggy and has approx. 3 gallons of fuel through it and this is the second pin it has broken. The buggy has never been raced and the engine was idling when this pin broke.
11-14-2014, 12:49 PM
#10
I don't know why the brand of fuel matters, the crankpin isn't galled at all so lack of lubrication doesn't appear to be the fault.
Having two crankshafts fail at the crankpin in the same engine lends me to believe either a manufacturing flaw or user error. At 3 gallons of fuel, the engine should be broke in well and not real "pinchy" so I'm gonna say either the failure is due to a defect in either the crankshafts or maybe a warped crankcase or bad bearings or hydraulic lock. I'd lean more towards a manufacturing defect based on what's been said. But what do I know.
Having two crankshafts fail at the crankpin in the same engine lends me to believe either a manufacturing flaw or user error. At 3 gallons of fuel, the engine should be broke in well and not real "pinchy" so I'm gonna say either the failure is due to a defect in either the crankshafts or maybe a warped crankcase or bad bearings or hydraulic lock. I'd lean more towards a manufacturing defect based on what's been said. But what do I know.
11-14-2014, 04:09 PM
#11
Thread Starter
I'm with you re " what brand of fuel are you using " but just for the record we use VP fuel. With the crankcase busted and a new case being acquired the bent case possibility if that was the problem should be solved, however I am tending to lean towards this being a manufacturing defect. I am giving some serious thought to pressing in a steel pin in the new crank's pin and web just to try strengthen the area which is breaking and which I think is the weak link here because of the hole in the pin. Your thoughts on this.
11-14-2014, 04:27 PM
#12
Ofna engines (which I think are made by Picco) are not known to fail in such a manner as yours, especially more than once in the same fashion. Personally, I'd not mess with the new crank. If it fails again, then either they had a bad run of parts or you're doing something wrong and likely the problem is probably the former. I'd replace the whole engine with something else and not look back if it happens again.
11-14-2014, 04:34 PM
#13
Thread Starter
We are giving this engine one last chance and are outfitting it with a new crankcase, crank and rod and if it happens again then it will become an expensive paper weight. Thanks to all who responded.
11-14-2014, 05:44 PM
#15
Ofna engines are not known to fail. I have seen very little on the half dozen forums I frequent in regard to any Ofna engines failing so catastrophically. I don't even see the cheapo Chinese engines failing like this; car engine or aircraft engine.
11-14-2014, 07:35 PM
#17
I'm not sure if any of my aircraft engines have hollow crankpins.... I've never really checked, but I think the aero engines are mostly all solid. Interesting.
11-14-2014, 08:32 PM
#19
11-15-2014, 05:55 PM
#21
The type thats pressed in,works with a one way bearing,which allows to free spin.
The type that fits in the end of a crankshaft with a spring works off the spring.So you cant have
a fixed one with out give,or were it pops in an out.The spring keeps the tension on it against
the starter pawl.
The only way to change it,is to change the whole starter assembly,if you can even find one
that will fit.
The type that fits in the end of a crankshaft with a spring works off the spring.So you cant have
a fixed one with out give,or were it pops in an out.The spring keeps the tension on it against
the starter pawl.
The only way to change it,is to change the whole starter assembly,if you can even find one
that will fit.
11-16-2014, 09:24 AM
#22
Thread Starter
As I mentioned in an earlier post I have removed the recoil start assembly, changed the back plate and now use a starter box so doing my proposed mod to the crank pin should work just fine.
11-16-2014, 11:11 AM
#23
The non pullstart crankshaft isn't different than the pullstart crank? Personally, I think you're asking for trouble by pressing a dowel into the crankpin. But if that's what you're set on doing, I look forward to seeing how things work out. Do let us know.
11-16-2014, 11:12 AM
#24
The non pullstart crankshaft isn't different than the pullstart crank? Personally, I think you're asking for trouble by pressing a dowel into the crankpin. But if that's what you're set on doing, I look forward to seeing how things work out. Do let us know.
11-25-2014, 12:12 PM
#25
Senior Member
Join Date: Feb 2007
Location: Somerset, UNITED KINGDOM
Posts: 2,324
Likes: 0
Received 0 Likes
on
0 Posts
The spring and pin arrangement would be my lesser choice of the three pull/roto/one way bearing options that I can think of...but that would not be because I think the crank pin would shear off...