Problems with 1.20 2 stroke

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James Stewart
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Problems with 1.20 2 stroke

Postby James Stewart » July 7th, 2014, 12:59 pm

Afternoon all. I am having a few problems all of a sudden with my Evolution 1.20 2 stroke glow engine. It rather ruined the flying side of my Strathaven airshow and I am still puzzled as to why it has happened all of a sudden.
To begin with this engine was run in on the aircraft and as such was inverted the whole time. Apart from having the tank higher than the carb (which induced the engine flooding if it was sitting long enough) there were no problems. The engine was run in with accordance to the instructions and with a few tanks of fuel through it there were no problems. A week later the aircraft was successfully tested at Glenrothes and there were no problems with the engine still. A few days later the aircraft was flying again and the second startup took the propellor and spinner off and this is when the problems began. As such every third or fourth time I try to fly this model the spinner and propellor are loosened on startup as if the engine has gone hydraulic. However, this as I have tested even happens when there is no fuel present. A few members with many years experience pointed out at Strathaven that the compression could be too high and this coupled with a powerful starter could be causing this issue. Also after inspection I found that the original Evolution glow plug and a new one I had fitted were both cracked. Even now while having a look at home the engine is almost impossible to turn over now. I shall try to post a picture later if I can but there seems to be a nick in the casing at the bottom end as if the conrod has hit the side on rotation. Has anyone come across this problem on any engine? I'm rather gutted as I havn't had this problem before and when it runs it doesn't miss a beat. But suddenly starting it is a major problem.
Thanks in advance gentleman

James

Ken Roddham
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Re: Problems with 1.20 2 stroke

Postby Ken Roddham » July 7th, 2014, 3:09 pm

James - It sounds as though there is possibly some damage/misalignment with the crankshaft/and or con-rod. This could have been initially caused with excess fuel in the cylinder when trying to start. This distortion could cause the piston travel to increase slightly and allow the piston to hit the plug tip. The engine needs to be stripped down and thoroughly checked - it may be possible to repair or may require some spares to bring it back to good condition.
Ken

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James Stewart
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Re: Problems with 1.20 2 stroke

Postby James Stewart » July 7th, 2014, 5:22 pm

Thanks Ken, I heard some say it could be too high a compression but I have a feeling you are right. If it was that problem it would have surfaced while engine testing. I'll try to gt it open this week and havea look Would the evidence of this be shown clearly anywhere or is it done to the movement of certain parts?

Ken Roddham
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Re: Problems with 1.20 2 stroke

Postby Ken Roddham » July 7th, 2014, 7:57 pm

James - You can initially take off the back cover 2 and check for any mechanical contact between the bottom end bearing and the bottom of the crankcase, and/or the inside face of the back cover.
You can then go further and take off the cylinder head and remove the liner and then piston and con-rod assembly. Check con-rod for straightness and the top and bottom end bushings. I can go into more detail with you with regard to c/shaft etc. when you get round to starting to check things if you just PM me, possibly with a photo or two.
Just take your time when you start to dismantle and watch out for shims and gaskets etc.
Ken

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James Stewart
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Re: Problems with 1.20 2 stroke

Postby James Stewart » July 7th, 2014, 10:58 pm

Cheers Ken, ill keep in touch.

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James Stewart
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Re: Problems with 1.20 2 stroke

Postby James Stewart » July 17th, 2014, 12:11 pm

Hi Ken, quick update (work seems to get in the way of all the fun stuff) so yesterday I took apart the engine. Back cover and cylinder head came off and I immediately noticed the absence of any gaskets and only one shim on the cylinder head (there should be at least two and a gasket). This could what is causing the compression problems. It may just make the difference. Is there any reason they would not have any gaskets on the engine or is this just another oversight and I have been unlucky?

Ken Roddham
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Re: Problems with 1.20 2 stroke

Postby Ken Roddham » July 17th, 2014, 12:43 pm

Hi James - It's a bit strange if you've had the engine from new and know it's history.
If there are no signs of mechanical damage and everything looks true then it would be worth it to reassemble according to the drawing with two shims for the head and a gasket set for the liner and back cover.
If it rotates ok then give it a test.
Ken

Bob Thompson1894
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Re: Problems with 1.20 2 stroke

Postby Bob Thompson1894 » July 17th, 2014, 9:19 pm

I should be very careful of using a starter on an engine that floods easily! You could easily bend the conrod. The old ASP 91 engines used to be too tight (abc piston/liner) and some people resorted to fine wet and dry paper to rub some material from the piston....

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James Stewart
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Re: Problems with 1.20 2 stroke

Postby James Stewart » July 21st, 2014, 4:11 pm

Ye exactly Ken, I've spoken to Horizon and i'm awaiting a reply.


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