Too much compression

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outboard
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Too much compression

Post by outboard »

Hi Guys
Having been really busy at work this year I've had very little time to play with my Seagulls, so it was a delight to get a wee break today and doodle about.
My FPC which has only had a minor clean started after a few pulls, to my delight as I know the carb will need a good clean. My second engine, an FP, has been sitting all year since I stripped it down and had to hone the bore as little pieces of wire broke off the crank bolts and got down into the piston and bore. I renewed the piston rings, but as I say it's been sitting all year. I gave it some petrol and after a few pulls it went well. My main concern though is, the compression. It takes a bit of turning the flywheel by hand, it's quite stiff. I nearly pulled it off the stand when I was trying to start it. Any suggestions? It wouldn't start after running for about 20 secs but that's not a problem, I would say that's down to dust probably. The compression thing is my main concern, I nearly done my back in trying to pull it to start.
On saying all that, what a buzz I got to hear it start. I'm not a mechanical person (until I got 3 Seagulls), so to strip one down completely and then see it roar into action was probably the reason I'm a member of this forum, brilliant.

Any suggestions on my compression problem would be gratefully recieved.

Gerard
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Re: Too much compression

Post by Keith.P »

I would suggest that you take the plug out first and turn it over by hand, if its still has some resistance then its not your compression that's the problem.
By the sound of it you don't have a compression tester, but that would tell you, A: you have very good compression, or B: you're getting old.
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Re: Too much compression

Post by outboard »

Thanks Keith, sounds like you hit it on the head, getting older. You're spot on, I don't have a compression tester but will try it without the plug and get back to you guys.
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Re: Too much compression

Post by outboard »

Hi, with the plug out there's still a fair bit of resistance. Could the driveshaft be too far down onto the gearbox housing.
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The Tinker
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Re: Too much compression

Post by The Tinker »

Something is starting to seize, remove the gearbox then try turning it over.
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Re: Too much compression

Post by Keith.P »

You just need to separate the engine from the gearbox, from the top or the bottom, what ever's easiest for you.
Then you can tell what's causing the problem.
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Re: Too much compression

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Thanks guys, will let you know my findings.
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Re: Too much compression

Post by outboard »

Hi guys

The words "sounds like something's going to seize" got me going. First, I hadn't put any oil in the gearbox, tut, tut, however this wasn't the problem. I've now removed the leg and stripped off the cylinder head. Here's my findings. The oil in the bore felt very gritty. There are a couple of scratches inside the cylinder head, this was caused by wire breaking off the bolts at the top of the crank, and getting into the bore (thus breaking the rings, hence the strip down). Could these scratches cause me trouble, like cause the piston to catch when I pull the flywheel? I was pulling the engine off the stand when it was getting snagged?

I'm now reverting back to basics for a strip down. Can I hone the scratches or should I get the head bored? Cheapest answers please, I'm a Scotsman.

Gerard
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Re: Too much compression

Post by Keith.P »

Hard to answer because there are scratches and scratches.

If the scratches are at the bottom end of the bore, then maybe you can get away with that without losing compression. Sounds like the wire coming loose has done some major damage and it sounds like you have dragging the wire up and down the bore. Being a Scotsman aside, a few photos would help in answering the questions and supplying a diagnosis.

But all in all it sounds like you have got to go back to basics and rebuild from scratch.
When I rebuild a motor I put it on an old drive tube led and turn it over to see if all is well before I put it back on the proper leg.

PS. At least you didn't fit the piston upside down!
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Re: Too much compression

Post by outboard »

Image
Hope this works, you can see the scratches quite well.
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Re: Too much compression

Post by Keith.P »

That looks quite deep, I don't think a hone is going to help.
If I was you, I would see about getting another barrel, not good news.
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Re: Too much compression

Post by outboard »

Hi Keith

Not the news I hoped for but not too drastic. I do have another engine which I think is bits and pieces as there's no number on it and things don't seem to match up right. I'll use that for spares. Thanks for the help.
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Re: Too much compression

Post by Horsley-Anarak »

outboard wrote:On saying all that, what a buzz I got to hear it start. I'm not a mechanical person (until I got 3 Seagulls), so to strip one down completely and then see it roar into action was probably the reason I'm a member of this forum, brilliant.
Gerard
This is what it all about, that little buzz when a pile of old junk is converted into a running engine.

Getting back to the scored bore, I would say that if you remove any burrs and build it up correctly then this engine will run.
It will prove harder to start, but it will run.

I still do not see why there is too much compression.

Does the crank spin freely in the crankcase, or is the big end bearing binding?

I do think that Keith is correct, start looking for a new cylinder. There are loads about.

H-A
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charlesp
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Re: Too much compression

Post by charlesp »

Did you gap the new rings? If not they'll be too tight in the bore.
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Re: Too much compression

Post by Keith.P »

By the looks of things the wire had made its way to the transfer port and had entangled with the piston, making it harder to turn over around TDC, feeling like it had too much compression.

Just a shame you have to start again.
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