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35S went pop

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TomEllingham Tue, 08/09/2020

Hi all,

I've had a lovely '91 Suffolk Punch 35S that I've been playing with for a couple of years and finally got the carb tuned in nicely and the blades backlapped (I'm learning along the way).

However a few weeks ago I started it up with no problem but a few seconds later there was a pop/bang/misfire and it stopped. Alas it wouldn't start again.

Here is how far I've got...

1. It has spark, looks ok to me. Plug is a bit dirty but I think I was running it quite rich before I honed in the mixture over summer.

2. Replaced the carb with an eBay replacement, mainly because I've had the other off so many time to clean I thought I might as well treat it to a new one.

3. Added a thimble of fuel, have also tried carb cleaner, directly in to the cylinder to see if I can get it to turn over. No luck. The best I got out of it was some smoke from the muffler.

I'm out of ideas now. Here is a picture of inside the cylinder if it helps, but there doesn't seem to be a fundamental flaw?

Any ideas?

Appreciate the help as always,

Tom

Forums

wristpin Tue, 08/09/2020

Try a new plug. If that fails check for a stuck / sticking valve and then for a sheared flywheel key.

TomEllingham Tue, 15/09/2020

Hey folks,

Replaced the spark plug but no change. I did see a pool of petrol coming out of the carb though (where the air filter would be) so not sure if that is from some frantic pulling trying to get it to start or symptomatic of another problem?

Took to the cylinder head off this morning. The gasket has disintegrated so will replace that, but not sure if that was a problem and/or just caused by me taking the cylinder head off. Valves opening and closing fine.

There is a slight clunk that I can hear, from the crankshaft area, as the cylinder head reaches the top. Worth investigating?

Tom

 

 

wristpin Tue, 15/09/2020

Before you go digging check for a loose coupling or clutch on the output end of the crank.

In the remains of the head gasket is there any sign of a specific burn or blow in one area.  Could be that your “pop” could have been the final failure of a weak area in the gasket. Were the head bolts tight?

TomEllingham Tue, 15/09/2020

Thanks Wrispin, will have a check.

The gasket has fallen apart on one side, but not sure if that was the final blow or it just disintegrated when removing the cylinder head. My hope is the former as that will make for an easy fix. I may even have a spare gasket from a box of spares I bought from eBay, so might be able to check today. Headbolts were tight as far as I know, I've never touched them.

TomEllingham Fri, 18/09/2020

Hey Wristpin,

New gasket fitted and started first time. This 35S now has a brand new carb, spark plug, air filter and gasket so should see it get a few more years of use now! Shame just as the cutting season is ending!

That pop must have been a very old gaskets last hoorah.

Tom