250 GN, the 100 mph project

[renault_megane_dci]

Very much out of the context.
The pictures were taken by a colleague to share with his colleagues and laugh at the bike.

I must admit it looks crap and modding a 250 soft custom in a manucured 600 roadster and up country is asking for troubles ...

[renault_megane_dci]

I have recently ordered parts from China (because the GN is still produced over there) including a Nickazyl cylinder.

There is also an oil cooler kit but I felt it wouldn't be that useful given the small amount of oil in the cylinder head is not gonna help it run cooler but on the other hand too low an oil temperature is detrimental to oil performance.

Expecting parts within a month time ...

[renault_megane_dci]

Parts got here in less than a week !

I asked a fellow engineer some feedback about the piston and cylinder with the old japanese part in hand and the opinion was the parts look OK.

Cylinder is sand casted so should be better as far as heat dissipation is concerned.
He pointed out some areas that needed work on the piston wich I did.

I then polished the piston crown (work is still in progress).
Valve cutouts were there from casting and the piston top had been flatted in a lathe as there was circular markings wich got away.
The piston alloy is quite tought compared to some other alloy stuff I have been polishing (SU carb for instance) so I quite feel reassured.


Hers is a view of the polished chamber too :


You might have notice the quench / squish area had a hard time pinging, it does point out the cooling must be improved if I want to run decent CR.

[renault_megane_dci]

Here is the oil reserve in the head :


It's fed from the camshaft journal and the cams dip in there to throw oil around.

The level is set from the cutout around the RHS inlet valve spring base.

I want to investigate if I can make this volume a touch bigger for better heat management.

[renault_megane_dci]

Exhaust ports :


The LHS port is modded.
Used to flow much better than the other coked up port until I cleaned said port ...

The good point is that the polished up port should transmit less heat to the head ...

[renault_megane_dci]

Well, regarding what I found in the sump tonight, the bike is not about to hit the road anytime soon :



The rod doesn't move freely enough on the crank either and has some axial play (but not radial).