200 cylinder Identification port maps added

[Adam_Winstone]

Mike,

If you have a copy of it (if not, why not?!) go and have a look at the standard SX200 port measurements quoted in the 60's tuning manual, which I understand is available in PDF off the web somewhere.

Season's greetings.

Adam

[Adam_Winstone]

Following on from comments long ago...

"5. The original number stub TV200 barrels that I have are quite different again and fall into 2 camps; early ring breaker and later non-ring breaker. Both are untouched port-wise but it is worth noting that my later narrow exhaust port TV200 barrel is a number 1, whereas the earlier wide port ring-breaker is a number 3, which supports the statements of others that the stub numbers probably do not represent a chronological / linear development/revision process but probably have a manufacturing significance (e.g. cast number, production line number, batch, other?)."

... I've just picked up a seemingly unmolested TV200 barrel with number 2 on the stub, meaning that I now have a 1, 2 and 3. Once I've got this cleaned up properly and can see whether it has had any porting work done or is virgin, it'll be interesting to see if/how the porting differs to the 1 and 3. I'll let you know.

Adam

[Adam_Winstone]

Well, after a good clean up of TV200 #2 I can't see any signs of porting work to the cast faces of the ports and this again shows why the TV200 got the 'ring breaker' nickname! Of the 3 original wide port GT barrels (assumed early) that I've had to measure, the exhaust ports come in at:

Gary N's barrel (number stub not recorded but I can still find out... he allowed me to identify it and take tracings before boring to 225 and adding a boost port + reed!) = 19mm x 47mm (70.6% of 66.6mm bore)

GT stub #3 = 18.5mm x 46.75mm (70.8% of 66mm bore)

Latest #2 = 19mm x 48mm (72% of 66.6mm bore)

Whilst the relatively short durations (low heights) will have given limited time for rings to drop into ports to break, the 70+ % of bore width does suggest that the rings were not very well supported and goes a long way to explaining the GT's 'ring breaker' reputation. Whilst a totally standard GT might have been ok, it would certainly have been on the edge of unreliability. The other version of the GT with a 20mm x 40mm port at 60% of bore was far less likely to drop a ring but also less likely to pull the 4.4:1 gearing, with later 19 x 43/44mm SX/GP ports being that 'happy house' somewhere between the two.

Incidentally, this latest #2 barrel has obviously done a few miles (visible ring wear pattern at top of bore but no lip to be felt) on the thin ring Asso that it came with so it does suggest that ring breakage wasn't an immediate problem with this piston... but the heavy seizure marks on the piston show that not all was well

Adam