ffkiwi

fiery-the more you delve-the more you find out how little you know-Jon Fletcher (a man whose skills I have immense respect for.......) and I correspond from time to time-and last year (or it may have been 2010) there were a lot of emails pinging back and forth between us about Allbon Darts. He's been sent a couple to work on and restore-and by swapping photos we discovered quite a few variations in cylinder porting-far more (4 or 5) than any of the magazines had ever hinted at-and coincidentally collectively came to the agreement that the very early Allbon Darts were a lot better than the later ones-not so much in quality of production-but in those subtle porting changes-and the timing changes that resulted.
.........for a start, DC Darts all have a fibre washer under the exhaust flange to seal the join-(look at the photos I posted earlier-and compare the DC Darts with the Allbon Darts) a paper gasket would do the job just as effectively-but be a little fragile-the fibre washer raises the liner by a significant amount-at least 1/32-1mm-which would be sufficient to change the exhaust and transfer timing. Did DC do this deliberately to alter the timing-or was it merely coincidental-that they chose to use a fibre washer for durability and ease of production? With a fibre gasket-and more compressibility, you could dispense with grinding the underside of the exhaust flange-leaving it as machined thereby saving yourself an additional machining operation?
...sometimes the reasons for change may not be clearcut...................look at the pic below-which shows three of my AM35s (there are two AM25s also mounted on the block, but they're deliberately out of picture)-all three are different-(and I have two more of the pink headed ones-both different!)-the left hand one has pink fins sitting atop a full crankcase width cylinder flange, the next one has red fins, a narrower exhaust flange, and standoffs at the base of the fins-the one on the right does not have the standoffs. Now there is no literature (meaning 'Aeromodeller' or 'Model Aircraft') mention of any marks or different models of the AM35 (though there was a Mk1 and Mk2 AM10, 15 and 25.......) yet these differences are real. Dave Hipperson-the former UK FF flier tells me he's identified at least 6 variants of the AM35......
This all begs the question-where/how do you distinguish between a variant, a model, a series or a Mark? The manufacturers may have their opinion, the users another-the collectors (who are usually the pedantic and fussy ones) a third...........
On another forum, I have been trying to untangle the confusing production history of PAW engines and model numbers-without a huge amount of progress-other than understanding that this is going to be challenging and time consuming! But for example-it can be critical if trying to obtain spares, if the crankshaft for example, was altered between one model of PAW 249-and the next (and worse still if you can't identify for certain which model you have............)
So if the magazines of the time make no mention, it is very hard thirty or forty years later, to account for changes in engines-unless you are lucky enough to run into someone who worked at the factory, and has a good memory...............

ChrisM
'ffkiwi'