Crank case identity

[griffon380]

Hi,
One on the right is my 380 QUB
One on the left was bought on ebay.
Can anyone identify the strange shaped ports or has someone just taken a file to a twin port and went mad

Engine number is GPE3/611

Craig

[dave higgins]

Hi griffon 380, looking at my 380 qub barrel, the transfer port footprint is the same as the one on the left, so i would assume, that there was a bit of production casting overlap between both crankcase & barrel & someone has tryed to equalise the difference to aid gas flow.
I have not got the crankcases here, to check, but from memory, i can remember that the crankcase ports were not symetrical to the barrel, but possibly not to that degree.
I did not remove the excess material from mine, as the material removed would have increased crank case volume & reduced the speed of air flow/transfer pressure, but i think it is a case of swings & roundabouts in this case, i would not have any problems using them. hope this helps.

[46T Sprocket]

Hi,
One on the right is my 380 QUB
One on the left was bought on ebay.
Can anyone identify the strange shaped ports or has someone just taken a file to a twin port and went mad

Engine number is GPE3/611

Craig

Hi Craig,

The set on the left has definitely had work done on it to open up the transfer area. It would be interesting to see if the barrel had been worked on to match. Along with a few other tuning tweeks to a 2 stroke motor you can get a big boost in power by opening up the transfer ports. Basically you are getting more mixture in to be compressed - and that creates a bigger explosion when ignited.



David.

[dave higgins]

Hi david, that is true of large ported , short stroke motors, but in longer stroke units with smaller ports, increasing the primary compression, ie adding stuffers or full circle flywheels, increases transfer air speed which gives a faster jet of fuel mix into the c/chamber,
I suppose the griffon unit does falls closer to the former rather than latter.

[griffon380]

Thanks Dave and David, unfortunately I don't have the barrel so will never know if they where "matched up" or not. Engine number shows it as being a twin port if that makes any difference.
As always, thanks for your help and comments
Craig

[46T Sprocket]

Hi Craig,

When you do get to the assembly part of putting it all together, check the barrel you have matches one of the two cases. Easily done with a paper tracing taken from each case and matching it up to the barrel.

What I mean is if you use the one on the left with the modified cases and it doesn't mate up with the transfer ports on the barrel you will have a big step twixt the two which will interrupt the gas flow. It will run but not as well as it could. I would be fairly sure the cases on the right are probably near standard. Dave H has indicated the likelyhood of that in a previous post.

I can’t say myself, 250cc Challenger & Silverstone barrels are as far as my experience goes with Greeves motors. I hope to remedy that with a Griffon at some point in the future.

Good fun innit!

All the best.
David.

[griffon380]

Fun does not even come close:roll eyes: