ET: Engine (Twin) Twin e-starter options?

Peter Holmes

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Francois Grossett fitted my starter a couple of years ago, and so far it has worked fine, but I run a pretty soft 998cc engine, Francois definitely does not recommend the use of the decompression lever, or any decompression device, I believe that Trevor Southwell developed the Grossett starter along with Francois, I think Trevor drifts onto this forum now and then, perhaps he could inform us why it is considered better not to decompress, since mine was fitted I have not used the decompressor and all is well, does gradually easing the decompressor of during starting predispose the engine to back fire, which we all know is considered fatal.
 

macvette

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Francois Grossett fitted my starter a couple of years ago, and so far it has worked fine, but I run a pretty soft 998cc engine, Francois definitely does not recommend the use of the decompression lever, or any decompression device, I believe that Trevor Southwell developed the Grossett starter along with Francois, I think Trevor drifts onto this forum now and then, perhaps he could inform us why it is considered better not to decompress, since mine was fitted I have not used the decompressor and all is well, does gradually easing the decompressor of during starting predispose the engine to back fire, which we all know is considered fatal.
I had a 1600 cc 1999 Yamaha Roadstar carburettor model, it had solenoid operated decompression and currently own a 1990 Honda GB 500TT which has an automatic mechanically operated decompression acting on the OHC.
It seems these companies have no problems using decompression with electric start so maybe its the timing of the release of the manual decompressor which causes the problem.
 

Comet Rider

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A friend in my section has a Shadow on 8.5:1 pistons c/w Grosset starter and uses the HD style automatic decompressors all the time, and has had no problems to date,
 

greg brillus

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When discussing this topic with Ken Horner he and I both agreed that the less number of cylinders on an engine the harder it is for an electric starter........But a big "V" twin is particularly bad because the power pulses are close together and this makes the engine similar to a giant single. By opening the throttle you instantly increase the volumetric efficiency of the engine, so this makes cranking very difficult.........Mac has made the most valid of points that most makes of modern bike engines do in fact use some form of decompressor in their valve train, usually some centrifugal weighted device that throws out upon engine start to regain full compression on that cylinder. The large capacity Harley/ S&S engines use a solenoid in the head.........On Terry's newer top end kits they have prevision for one of these solenoid valves to screw into a 12 mm thread with a tiny hole that passes through into the combustion chamber between the two valve seats......This seems to work quite well, i installed one of these kits on a Comet a couple of years back, and chose to use a horn button on the left side handle bar as a compression release........It worked very well for turning the engine just over TDC for starting, although it wan't quite big enough to effectively stop the engine like a stock valve lifter, but it had coil ignition anyway so that needed to be switched off to kill the engine.
 

Oldhaven

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Greg,
Just curious as I will be using a HD solenoid CR on my TPV top end Comet project. Do you recall if the bike would kick start and run while continuing to hold down the button rather than just using it to get over compression? I would like to use the CR in a similar way as the valve lifter lever. Of course if I just got my act together and finished it I would already know this...

It worked very well for turning the engine just over TDC for starting, although it wan't quite big enough to effectively stop the engine like a stock valve lifter, but it had coil ignition anyway so that needed to be switched off to kill the engine.


This question does have some relevance to e-start. I have a chain saw with a push button CR and after it starts it will continue happily running at low compression until I rev it and the CR closes. I would think that this way of not completely decompressing the cylinder, effectively lowering the compression ratio by a small leak, would make it easy on the starter system by not releasing the solenoid button until after a start.
 
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Bill Thomas

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We fitted a 14mm thingy to Ron's Comet, You just push it open and Kick, It's like we left the piston out !.
Ron didn't get on with it at first, But that was with a Mag' , That we think was not good,
After we fitted a "D" Distributor it was fine.
 

davidd

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HD Auto Compresion Releas.JPG


HD ACR 02.JPG


I believe that the size of the socket is 13/16" and the torque spec is 17-19 lb/ft.

David
 

Monkeypants

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Greg's description of the backlash makes me glad I went thru the effort to fit the Newby belt drive and rear wheel cush drive. I wasn't thinking about e start and backlash at the time, so it's luck rather than good management.
Another type of compression release, one that may not have been mentioned yet, is the type used on the 490 Maico MXer. This engine is at 12 to one CR and very difficult to kick over without the compression release. The compression release is a manual type, but does not release all of the compression.
It effectively reduces the 12 to one to about 8 to one for starting.
The engine starts nicely on 8 to one and then you release the lever to get going. Really get going!
I wonder if this type could be used on a big bore hi compression Vincent engine to reduce load on the estart? Or to negate the need for estart. This would really appeal to me as I really don't want to add the complexity and weight of an estart to the bike.
Would the bike still start easily with some of the charge bled off? Probably only one way to find out!

On edit- I see now that Oldhavens chain saw has a similar compression release, but automatic rather than manual.

Glen
 
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greg brillus

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The solenoids that David posted a picture of above are the exact ones to use, only you need to make up a simple banjo arrangement to move the gases away from the cylinder head.........I don't really see the gases as being an issue, but it can make a slight mess of either fuel or oily residue coming from the valve assembly. Indeed the Royal Enfield cable operated ones that Tim and I know and have used, can tend to do this as well. To answer Gene's question, No sorry I don't remember trying to start the engine holding the decompressor in whilst cranking the engine..........I feel this would tend to work where an electric starter is involved.........Generally once you get the piston just over TDC then a good kick will start the engine no problem. Of course if you are using a Norton AMC gearbox you generally need to turn the engine more past TDC for a good start on the kickstart lever on account of the different kick/crank ratio within the gearbox. The fear factor of using the stock valve lifter on a twin with an electric start is minimal in reality verses the strain on the starter..........It seems obvious that reducing the compression load will definitely help the engine/starter combination even if the reduction in compression is only a partial amount.
 
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