post gasket blues

[ade]

i replaced the cyl head gasket on my '67 850 TL, after skimming head etc.

I have not been able to get it started since.

I've changed the leads, points, rotor arm, condenser, coil, timed it no. 1 at 10mm before mark on flywheel, not a chance of starting.

Distributor can only go in one way (Ducellier), leads assembled 1-3-4-2 clockwise.

I've got fuel and a spark.

Compression, cold (obviously), is 130 (no.1 nearest gearbox), 150, 140, 132 psi.

These are low, i think, but maybe a hot engine increases these figures?

What is worrying, is that cylinders 3 and 4 show oily deposits on the plugs.

When i try starting, it coughs and splutters, then it let out an almighty bang.

I retired, hurt.

Any crumbs of advice or statements of the bleeding obvious appreciated....Adrian

 

[bantamallan]

sounds like timing 180* out recheck distributor position or move plug leads .

 

[Geoff in the Gully]

Sounds just like a problem I had recently starting a long dormant engine. It was what Bantamallan says - timing 180 degrees out.

It did seem like it wanted to start but never gave more than a single cough at a time.

 

[ade]

engine

i will check again, but i cannot see how the dizzy can be in the wrong position with the offset slot drive

 

[Geoff in the Gully]

That's what got me as well at first.
It's not so much the dizzy that's in the wrong position but the crankshaft.

If it's a whole turn out, the dizzy slot is in the right position but it's piston 4 instead of 1 that's ready to fire. The valves in 1 are open and if there's some fuel vapour left in the cylinder it can 'fire' with a backfire through the carby or a cough out the exhaust. Depends on whether the timing is advanced or retarded as to which you get - I was turning the dizzy left and right trying to find the 'right spot' and I'll bet you've been doing the same.

It's a real easy test to simply swap the leads 1 with 4 and 2 with 3.
Actually, the hardest part is deciding to do it! My brother and I argued for 15 minutes that we'd done everything right, that it couldn't be that, etc before doing the 30-second test to prove us both wrong. The engine fired instantly - proof positive we we're both wrong. We still don't see what we did wrong!!

 

[ade]

well, its still not started, i've tried swapping leads, no good

after a good 30 secs of cranking, then taking plug out, it hardly smells of fuel...i'm wondering if theres a fuel starvation problem...took carb cover off but float chamber had fuel in....

any other suggestions?

 

[mojobaby]

Hi Ade, what everyone is trying to say is that for every one rotation of your rotor, there are two revolutions of the crankshaft. So if the crankshaft turns once, the rotor will be at 180 degrees, or halfway way around and will point at No 4, furthest from the flywheel. Had me fooled for a long time too.

Have you had any work done to your carb lately? Perhaps it just needs a clean. I think after all that cranking your plugs should be wet! Just because there's fuel in the chamber it doesn't mean that its flowing through.

I've also read on this site that if you skim your head then a thicker cylinder head gasket should be fitted.

Hope you get it sorted

I've just had the same problem on my chainsaw. dry plugs! I took out the needle valve in the float chamber and cleaned it. Worked perfectly well afterwards

 

[ade]

thanks mojobaby, i just saw fuel in the float chamber and thought thats ok, but perhaps not.....on the dizzy posn, i just looked for both valves shut and thats the cylinder that should be sparking, but that may not be accurate enough...i'm sure its something simple?!