Outboard mystery.

[VicS]

I meant excessive smoke,everything said so far i have done like extending the plugs,i did extend the plugs to the last 2 threads still massive compresion.I have come to the conclusion that the exhaust port might be blocked but what is the chance of that in 2 cylinders? Anyway i will put a scope camera down to check them,does anyone know how far down the ports are? Oh what a bloody nightmare! Thanks all again.Ronnie.

The ports only become opened in the lower part of the stroke. To inspect them you will need to take each piston in turn down to the bottom of each stroke

Like Richard i doubt if they can become blocked, but they are closed off by the piston once it has risen part way up its stroke anyway. The compression you feel is that caused by the piston compressing the fuel and air mixture into the relatively small space that is left at the top of the stroke. It should, of course, be felt as a gradual increase as the piston rises.

Perhaps the combustion chambers have become so heavily coked that the compressions have risen to such a high level that it is cause your cranking problem. The compression tests I suggested earlier should throw some light on the situation if that is so.

 

[TSB240]

I used to play around with two stroke kart racing engines and the only two things that caused the same symptoms as this was if we had an engine with the squish set too small or a piston ring was slipping into a transfer port.

If its the first try putting a bit of solder wire through the plug hole and check to see how thin it is compressed at the edge of the piston once turned through TDC If its less than .25mm then either the engine may have been rebuilt without the correct gaskets or the head has been over skimmed. Surprised if it was running in that condition?

If its a piston ring then what can happen is they twist in the groove (only happens under compression) and get pushed out by the little pin in the groove that stops the ring twisting round any further. If this pin is worn the ring end can then get pushed out and it will interfere with either the transfer or exhaust ports at some point. Cranking over the engine or running it will usually snap the ring off. It was quite common when opening up the transfer ports too much that in race conditions you would only have one top compression ring left at the end of a race the oil control or second ring was usually in bits in the exhaust. Interestingly we got at least 3,000 more rpm and a lot more speed with only one ring but the pistons had a habit of exploding at around 20,000 rpm!

Strip down to piston and check rings and bore for damage would be my recommendation. Cant see how you could have too much oil and hydraulic lock in a stored engine that you have not been able to start?

Steve

 

[MonniotC]

"If this pin is worn "
That reminds me that back in my Lambretta tuning days about 50 years ago, I had more than one instance of the little pin coming out altogether, allowing the ring to rotate round the piston until one end got caught in a transfer port. Instant disintegration of piston!

 

[RichardS]

I used to play around with two stroke kart racing engines and the only two things that caused the same symptoms as this was if we had an engine with the squish set too small or a piston ring was slipping into a transfer port.

If its the first try putting a bit of solder wire through the plug hole and check to see how thin it is compressed at the edge of the piston once turned through TDC If its less than .25mm then either the engine may have been rebuilt without the correct gaskets or the head has been over skimmed. Surprised if it was running in that condition?

If its a piston ring then what can happen is they twist in the groove (only happens under compression) and get pushed out by the little pin in the groove that stops the ring twisting round any further. If this pin is worn the ring end can then get pushed out and it will interfere with either the transfer or exhaust ports at some point. Cranking over the engine or running it will usually snap the ring off. It was quite common when opening up the transfer ports too much that in race conditions you would only have one top compression ring left at the end of a race the oil control or second ring was usually in bits in the exhaust. Interestingly we got at least 3,000 more rpm and a lot more speed with only one ring but the pistons had a habit of exploding at around 20,000 rpm!

Strip down to piston and check rings and bore for damage would be my recommendation. Cant see how you could have too much oil and hydraulic lock in a stored engine that you have not been able to start?

Steve

In either of those issues why would the engine free up completely once the plugs are removed?

Richard

 

[MonniotC]

If the engine turns freely with the plugs removed then the question of rings getting stuck in transfer ports or piston(s) hitting the squish platform are non-starters. The fact that the problem persists even when the plugs are backed nearly out eliminates piston(s) hitting plugs. This still leaves a few possibilities:
1) Stronger arm required.
2) The pull-starter ratchet mechanism is locking solid somehow when under load (plugs in) but operates freely when unopposed (plugs out)
Probably.

 

[bigman1]

Might sound crazy but would a cordless impact wrench make a cheap electric start option? At what torque does the rachet hammers kick in?

 

[RichardS]

Might sound crazy but would a cordless impact wrench make a cheap electric start option? At what torque does the rachet hammers kick in?

Plenty enough torque to turn an engine over ... but what are you going to attach it to on the motor?

Have you actually decided that the problem is that you need more "welly"?

Richard

 

[VicS]

Plenty enough torque to turn an engine over ... but what are you going to attach it to on the motor?

Have you actually decided that the problem is that you need more "welly"?

Richard

You could remove all the recoil start system and and using the appropriate size socket turn it via the flywheel retaining nut.

 

[RichardS]

You could remove all the recoil start system and and using the appropriate size socket turn it via the flywheel retaining nut.

And have to remove and replace the cowling every time you want to start the engine? :ambivalence:

Richard

 

[TSB240]

In either of those issues why would the engine free up completely once the plugs are removed?

Richard

In the first case plug removal means extreme compression is released when plug removed. In second case as indicated ring only expands into port when put under compression no plug no compression simples.

 

[RichardS]

In the first case plug removal means extreme compression is released when plug removed. In second case as indicated ring only expands into port when put under compression no plug no compression simples.

Simples maybe ..... but no cigar.

Richard

 

[bigman1]

Hi Richard,
I am leaning toward more "welly" but not sure till i get the cam. down in bores,the two cord pullers are big strong men,
but maybe technique has a place here.Power start would make sense for me,but this engine was in such good condition
i could not refuse it. Thanks to everyone for their input.Ronnie.

 

[dingdongs]

Too much fuel under the piston not allowing transfer ports to have atomised mix. Invert engine with plugs and fuel removed and see if fuel can be seen coming out the barrel. Crank slowly. If all seems well plugs back in and start normal starting procedure with maybe heated plugs to aid a good first run.

 

[RichardS]

Hi Richard,
I am leaning toward more "welly" but not sure till i get the cam. down in bores,the two cord pullers are big strong men,
but maybe technique has a place here.Power start would make sense for me,but this engine was in such good condition
i could not refuse it. Thanks to everyone for their input.Ronnie.

You're absolutely right .... it's not all about power but equally about technique. Obviously with larger engines the power ingredient become more important but the technique element is always there.

We have a small single cylinder 2.5 HP which starts first pull but my Wife really struggles to start it and usually gives up. It's definitely not because she doesn't have the strength .... she's in the gym most days .... but it seems that as the cord extends and compression begins to build she instinctively starts to reduce the strength of her pull almost as if she has an instinct that it's going to break so she backs off. The engine still goes over TDC but it needs to "snap" over TDC to start and it doesn't get that so it fails.

I'm equally to blame as I seem unable to explain clearly what exact technique is required.

Richard

 

[MonniotC]

Bump.....
Well OP, did you find the problem??

 

[lw395]

Hi Richard,
I am leaning toward more "welly" but not sure till i get the cam. down in bores,the two cord pullers are big strong men,
but maybe technique has a place here.Power start would make sense for me,but this engine was in such good condition
i could not refuse it. Thanks to everyone for their input.Ronnie.

I think a bore inspection is called for.
I'm not sure the 'ring catching in the ports' idea is likely, but there has to be something wrong with it!
When I try to pull-start mine, it does not feel like pulling against a solid object, you can feel that you are dealing with a piston compressing gas.
Is it possible that a bearing is rough, and the compression on the piston is enough to lock it up?