Author Topic: EW600 compression  (Read 1080 times)

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Offline geomellish

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EW600 compression
« on: 12 Oct 2017 at 16:41 »
Searching for a solution to my overheating EW600 - a cold compression test came out with 50psi front and 37psi rear.... too low, I think, and uneven; the engine is going to have to come out and apart to investigate.

Firstly does anyone know what the compression ought to be?

The valves, guides and springs were replaced five years ago (not by me) so I'm guessing the rings and/or pistons might be the problem.

I've checked the valve and ignition timing and fixed the induction pipe (see http://www.douglasmotorcycles.net/index.php?topic=6715.0), re the overheating - does low compression affect the heat produced?

Any thoughts or advice gratefully received. George


Offline Dewey

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Re: EW600 compression
« Reply #1 on: 18 Oct 2017 at 00:50 »
Hi there. The low compression can certainly make the engine run hotter. In order to get enough power to do what you're used to, you find yourself having to open the throttle more to compensate for the engine running less efficiently. That lost efficiency is power wasted in the form of heat. This is true for all engines. If you find the engine is blowing out a lot oil more than usual it's probably worn rings. It can just as easily be burned valves, usually the exhaust. The thing to do is find a way to lock the flywheel when the piston is at top dead center compression stroke and apply compressed air in the spark plug hole, 15 to 20 psi is enough. If the exhaust valve is leaking you will feel and hear it coming out of the muffler. If it's an intake valve it will be evident at the inlet of the carburetor. If it's rings it will be evident at the oil filler, although some leakage here is expected. I'm talking about a very noticeable amount of air escaping. Do this on both cylinders making sure both spark plugs are out during the test.

The simplest way to lock the flywheel is to put it in high gear. My money is on the exhaust valves.

Dewey 

Offline graeme

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Re: EW600 compression
« Reply #2 on: 18 Oct 2017 at 22:26 »
You can also do a wet test. Check the compression with a compression gauge, then squirt a bit of oil into the cylinders. If the compression comes up, the fault is worn rings; if it doesn't, the valves are leaking

Offline Ian

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Re: EW600 compression
« Reply #3 on: 23 Oct 2017 at 22:47 »
I had endless problems with my E28 rear cylinder (hopefully fixed now). The main culprit ended up being a missmatched head and barrel. The spigot on the barrel was too deep for the recess on the head so a standard head gasket didnt quite seal. I initially just put an extra gasket in which fixed it - but then machine a bit off the barrel and its all OK.

Make sure when you assemble that there is no carbon buildup in the recess on the head !

Offline geomellish

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Re: EW600 compression
« Reply #4 on: 25 Oct 2017 at 13:41 »
Thank you for your replies, Dewey, Graeme and Ian.  I still wonder what the compression figure ought to be for this bike - or indeed a 350 EW.  Does anyone know? Regards George

Offline oily bloke

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Re: EW600 compression
« Reply #5 on: 25 Oct 2017 at 17:16 »
I'm not totally sure but my EW350, running flat top CB750 pistons, is around 6 to 1. I haven't got an adapter for my compression tester so I cannot give a PSI value. Runs really well. I had a Raleigh single before the Douggie and that was a woeful 4 to 1 until I breathed on it a bit and it ended up at 6 to 1 and went really well too. Hope that helps
Andy

Offline Ian

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Re: EW600 compression
« Reply #6 on: 30 Oct 2017 at 03:06 »
I think with these the key is to have similar compression both cylinders rather than worry about the numbers. The inlet manifold is bad enough on them without a lazy cylinder !