Forum

[Mark M]

Dennis, I thought the same thing but reading Phil's post I think he means that he can vary the compression ratio with the plates. I believe this is recommended if you use our Hosts forged piston and alloy barrel?
REgards, Mark

[Alan R]

Hi guys ------------ there is a slight "down" side to all this..With my No.1 Bullet I'm currently using our hosts 8.5 forged piston in an alloy barrel.( At that time the Standard compression FORGED piston wasn't available ).. Last year I fitted their oversized inlet valve and also a 2mm plate to retain a little bit of tractability and so continued to use the cheapest grade petrol..My guess is the CR came out at 7:1 approx....Several unexpected things happened all at once}--- a)Replacing the inlet rocker cover became virtually impossible as the WHOLE Barrel/ Head assy. had now risen by 2mm....b) Starting became easier and ...c)The inlet valve failed after just under 1 years running (say 1,500 miles) with lots of small, metallic-like deposits on the valve seat face......I believe several others posted with the same problem at that time ?? The valve was returned to the manufacturer via Hitchcocks for examination...It was later returned with the comment that the valve was sound and the use of low-grade ( Ethanol blend by inference ) fuel was to blame.................. I've since removed the plate and have a standard valve assy in use now, and buy premium grade fuel only...I have recently cleaned - up the O/S inlet valve in my lathe and am currently re-building the spare head, hopefully to be fitted before MadMike's Sunday...Just to round-off the story I have a 19t sprocket and a 28mm Mikuni jetted to RIGGER'S sizes (Where is he lately ??)

[Phil Ashbrook]

Dennis you have made a good point and until I do a real comp ratio calc I doing very rough estimates , I might be only 8:1 , skimming the head and skimming the barrel with lip reduction was not the best thing to do but I wanted complete up down barrel hight ajustment , I fitted the 2mm barrel plate as a caution to my high lift camshafts and forged piston and the oversize exhaust valve .
In no way did I want those valves kissing the piston , my tuning is still not finnished as I want to fit the 612 longstroke crank but ran out of money , the 2mm plate will stay but I must do a plasticine valve clearance check .
The STD con rod and floating bush has limits to high comp set ups so I would rather run under 9:1 than over till I get that crank and roller big end and then I can hammer the engine without throwing a rod .
612 cranks are not cheap but worth it for high compression tuning .