exhaust port timings

[hendy]

How close to the top is it at TDC?

Squish is 1.4mm. Which I like.

[rosscla]

Sorry but that's doesn't really answer the question.

Let me try again, what is the distance from the top of the barrel to the edge of the crown of the piston at TDC?

Is the head recessed on that kit or does it have a gasket?

[hendy]

Sorry but that's doesn't really answer the question.

Let me try again, what is the distance from the top of the barrel to the edge of the crown of the piston at TDC?

Is the head recessed on that kit or does it have a gasket?

About 1mm.

Not recessed and I have 0.5mm gasket between head and barrel.

[Knowledge]

Hmm.

Ok, what about the distance from the bottom of the exhaust port to the top of the barrel? This should be a mil or so longer than the stroke. I suspect you are going to see a measurement that is 3mm longer than a 58mm stroke of the crank.

[hendy]

I suspect you're correct. I'll have a leisurely breakfast then measure.

Also, I sent that photo to the chap who tuned it for me and he says he'll do me a new one after christmas. I don't know him personally as I'm new to this lambretta lark but his reputation is good so I've no reason to doubt him.

If I were him i'd be wondering about the abilities of the engine builder so I'll take the engine to him fully assembled.

We all make mistakes so I won't name him.

[hendy]

Hmm.

Ok, what about the distance from the bottom of the exhaust port to the top of the barrel? This should be a mil or so longer than the stroke. I suspect you are going to see a measurement that is 3mm longer than a 58mm stroke of the crank.

Bottom of exhaust port to top of barrel is 62.6mm
Edge of piston at bdc to top of barrel is 58.9mm

[Knowledge]

Ok, kinda what I expected.

Now check this. When the piston is at BDC, do the bottom of the transfers and the bottom of the exhaust port all line-up? If the bottom of the exhaust port lies lower than the bottom of the transfers, then this is not a good thing.

Have a look and get back to the forum

[rosscla]

Sorry but that's doesn't really answer the question.

Let me try again, what is the distance from the top of the barrel to the edge of the crown of the piston at TDC?

Is the head recessed on that kit or does it have a gasket?

About 1mm.

Not recessed and I have 0.5mm gasket between head and barrel.

You could improve it by about that much by packing the barrel up 0.5 and dropping the head gasket, but that's not really going to improve it enough. A 60mm stroke would mean it would drop 1mm lower at BDC and you could add back the gasket or pack it up a bit more and do without, but you'd still be looking at a new crank and wouldn't have solved the whole problem.

I'd the guy's offered you a replacement then see how that looks.

[eden]

who ported the barrel?

[shocky]

who ported the barrel?

A man who makes mistakes ....