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1360 motor in place

Monkeypants

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It runs very well but is a beast to kick over, as expected. With the large displacement, high compression and generous squish bands, this was expected. I would say it is at the limit of what one should plan on kick starting. Luckily, the Pazon Special Ignition produces four big fat blue sparks at very low kickover speed, which is all I can manage. Starting on the rear cylinder is the only way to get it to roll thru a compression stroke. I managed to turn the kickstart into a pretzel when the bike kicked back lightly after getting too much fuel in the cylinders. So please excuse the very ugly modified kicker, it is not my finest work. It is braced up with webs fore & aft and will do fine until I build a sleeker version this winter.
 

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Monkeypants

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two spark plug holes in each head already, both in use and no place for a third. I dont think a different type of decompressor would be of advantage for kick starting as the stock item, once modified for Terry's Mk5 cams, works great, tho it is a complicated little affair.
The problem in starting is that no matter what decompressors are used, the motor must roll over top at least once under full compression in order to start. Fortunately, with the short space long space geometry, this just barely possible at the end of the long space before compression( rear cylinder) The big squish bands which Terry designed into the heads make this engine much harder to kick over than a standard head version would be at same displacement and cr. The compression buildup with the hemi head is more linera wheras with the squish heads you really hit a wall when bringing e piston up within 40 thou of the squish bands.
The extra lof the cams vs mk1 or mk2 is also noticeable on the roll up to compression. Because of the high lift(.440" vs .312 mk1 or .343 mk2, there is quite a
 

Monkeypants

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slowing effect on rollover as the valve springs get this extra squeeze. Terry was doubtful that the engine could be kickstarted and I can see why. As it is, my 230 lb weight is barely adequate to do the job, so all diet plans have been shelved.
Glen
 

vibrac

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the idea of the HD item is that there is no compression untill it fires and shuts the door the remainder of the gas then turns the motor (against the second open head) where again spark fires the cylinder and that door is shut as well the motor continues to turn and then the next spark gives a full throw it also has the advantage that you can position the correct cylinder to be first in the firing line. having run my racers on twin and single plugs what marginal effect it gives me I would gladly loose for easy starting,there is of course one extra place for decompressor (or 10mm plug?) firing-breathing via a 1/4 hole in middle of head twixt the two valve seats (thats how Ron Kemps Flash ran 2 plugs back in the day)
 

Monkeypants

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Tim, I can see how the Harley decompressor would work very well to soften things up for an electric starter, but with the minimal movement of the kickstart it needs one up and over at full compression, in the right spot with all of the riders weight plus the momentum of the flywheel to carry it all thru. Several Vincent people have told me to forget the two plug setup on the Vincent, however they all experimented with stock type hemi Vincent heads. The Prince combustion chamber is/much different and according to Terry, should be run with two plugs firing. This not only provides more power, it allows for the timing to be rolled back five degrees so that pinging is non existent, even at high compression.
I did look for a spot to drill a third hole, however there is no space. Again, quite different than Ron Kemps Flash in that the CC is long and narrow and quite small, very similar to those used in the Australian V8 supercars, as Horners also have copied.
The upshot is that it doesn't need anything changed nor do I need to try and adapt some/sort of electric start, as it starts very well now that I have adapted to the required start method.
 
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highbury731

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Twin plugs have far more effect with squish-bands, as with the Terry Prince heads fitted. So there's more to lose by going back to single plug. I have seen Husqvarna chain-saw decompressors on a Vin, these are similarly compact and I think fit in a 10mm hole. Don't know which would work better.

There's a video showing a set of manual HD decompressors being fitted to a bike here:
If I can see clearly, the heads have been machined with a 10mm hole for the decompressor in front of the spark plug hole

There's a video of a machinist modifying HD heads for their electric decompressor:

Manual Decompression Valve for Husqvarna/Partner K650 Active, K750 & K760
Genuine Husqvarna Part OEM No. 503 71 53 01
 
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