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Cilinder gasket

Posted: Mon Dec 02, 2019 8:19 pm
by Elie
does anyone know the thickness of the gasket under the cylinders of my rumi

Re: Cilinder gasket

Posted: Mon Dec 02, 2019 9:01 pm
by Elie
my question arises from the following, I have drilled cylinders on 42 and matching pistons, piston rings on 0.0016 opening pistons with 2 piston rings, a set of seals of a sport, everything mounted and now it appears that I only have 4.5 a5 kg compression pressure , think that on the few side, would make a thinner foot pack now but do not know how thick to increase the compression, how much compression does a single engine

Re: Cilinder gasket

Posted: Wed Dec 04, 2019 1:33 pm
by UHJ200
" it appears that I only have 4.5 a5 kg compression pressure "

Sorry but it would seem there is a translation problem, clarify please.

A thinner cylinder base gasket will lower the ports in the cylinder relative to the piston and will make a small alteration to the timing of all ports, not to be recommended.

Viewed through the exhaust port the piston crown should be "line-on-line" with the bottom of the port with that cylinder's crank at bottom dead centre.

Check the gasket thickness needed by using feeler gauges between the cylinder base and the crankcase mating face until "line-on-line" is found. Make an allowance for gasket compression.

Re: Cilinder gasket

Posted: Wed Dec 04, 2019 2:08 pm
by Elie
hello thanks for the response, to clarify the engine is assembled and I measure the compression through the hole of the spark plug and that gives 4.5 to 5 kg / cm think this is on the low side, I have to use the exhaust pots to the determine the thickness of the foot gasket with the feel sizes, I use a translation site, your method will use again thanks

Re: Cilinder gasket

Posted: Wed Dec 04, 2019 6:34 pm
by UHJ200
Remember that a 2stroke does not start to compress until all the ports are covered, a 4stroke makes better use of the stroke so you should not expect as high a reading for a 2stroke. Remember also, (I deduce), that at least the pistons and rings are new and therefore not bedded in. If my geriatric mathematics are right you are getting around 60psi which I'd say is not at all bad.

Unless you truly know the history of an old engine you cannot be sure of what may have been done to it, the barrels may have been skimmed at some time for instance, so trust nothing! Getting the edge of the piston lined up with the bottom of the exhaust port is as good as you can get. Gasket thickness to achieve that will be whatever it takes.

Re: Cilinder gasket

Posted: Wed Dec 04, 2019 11:08 pm
by Elie
thanks again, yes I was used to handling 4 stroke engines, a 2 stroke is new to me I followed your advice and the piston top is the same as the exhaust port so that's good, I get the 60 psi so that's good and indeed everything is new, it will be fine you have provided me with good information, as well as other members of this forum, when the rest is sprayed I can continue to build and test the engine, keep you informed of progress, greetings

Re: Cilinder gasket

Posted: Thu Dec 05, 2019 12:28 am
by UHJ200
Count yourself lucky mate! ;)
"Back in the day" when I rebuilt my Tipo there were no spares, no Forum, no nuffink :!:
I had to make everything from scratch, my own cylinder liners, pistons, rings and gudgeon pins! :roll:

Always happy to help if I can. :D

Re: Cilinder gasket

Posted: Thu Dec 05, 2019 9:16 pm
by Elie
now solve the problem with the gearbox control :D

Re: Cilinder gasket

Posted: Thu Dec 05, 2019 11:32 pm
by UHJ200
now solve the problem with the gearbox control :D

If you mean gear selection/jumping out of gear adjustments and corrections then there are lots of posts about this already on the Forum.

Other than the thorny subject of exactly how the factory went about assembling the right hand cover and those parts of the selector mechanism attached to it onto the crankcase remains unresolved but I think we have pretty much solved the rest.

The important thing to understand is the way the engine was designed, you have to get inside the mind of the designer. "Every journey starts with a single step", that step in this case is the joint line between the two crankcase halves. The whole engine and gearchange assembly is laid out along that line.