Bukh starting handle.

[LittleSister]

I used to ride big single motorcycles, where the position of the kickstart engagement in relation to compression, and the right speed to apply to the kickstart, were critical. That's because you had quite a bit of force in your leg, but little more than a single cycle of the engine achieved by each application of the kickstart.

By contrast, for Bukh (and similar ) marine engines flywheel speed is the thing you need (at least in theory). You won't be able to turn the handle past compression, so its the power of the flywheel that's carrying it over compression, and the faster it's going the more power there is available. It will take quite a few turns to get it up to the highest speed you can (before you start tiring), and it will be critical to be able to release the decompressor before the speed of the flywheel falls (and preferably while you're still turning the handle). I'm hoping to rig up some sort of system of cords so I can release the decompressor with my foot.

 

[James_Calvert]

A bit of cord in your teeth might do it...

 

[Poecheng]

In my defence, I have been discussing single cylinder Bukhs, not some namby-pamby -easy-to-start twin cylinder jobby

 

[VicMallows]

Another here who can start his BUKH20 from warm with no problem. I did even manage a 'next morning' start once with the help of a little easy-start. The big difficulty if you are on your own is the de-compressors: on mine they are linked and spring-loaded and need to be held open (not 'flicked on' !). I have indeed used a cord looped through a turning point and held under my foot.

The starting handle is pretty basic and it should be trivial to make one. Happy to measure the shaft diameter and pin size/position is you need that.

 

[LittleSister]

In my defence, I have been discussing single cylinder Bukhs, not some namby-pamby -easy-to-start twin cylinder jobby

Except the Bukh twin is just a doubled up single - each of the two cylinders is of the same capacity as the single, so the compression of each is just the same as the single. It's not like having the same capacity/compression effort divided in half.

 

[Poecheng]

Except the Bukh twin is just a doubled up single - each of the two cylinders is of the same capacity as the single, so the compression of each is just the same as the single. It's not like having the same capacity/compression effort divided in half.

I was trying to get my head round this last night. If the flywheel is the same weight then I think you would be correct. If the flywheel is of greater mass then it would use that greater mass to start one cylinder (not two) and therefore probs an advantage. Don't know the answer :encouragement:.
Also with a twin , surely if you even get a "spark" on the first compression, you rapidly bring cylinder 2 up to fire whereas on a single it has to go through the whole cycle to catch again.
I am sure I have started twins in the past but never a single Yanmar or Bukh - I am sure I have started a Sabb with the ignition helper.
Anyone started a Bukh DV10 by hand?

 

[LittleSister]

I was trying to get my head round this last night. If the flywheel is the same weight then I think you would be correct. If the flywheel is of greater mass then it would use that greater mass to start one cylinder (not two) and therefore probs an advantage. Don't know the answer :encouragement:.
Also with a twin , surely if you even get a "spark" on the first compression, you rapidly bring cylinder 2 up to fire whereas on a single it has to go through the whole cycle to catch again.

Good points. I stand corrected.

Anyone started a Bukh DV10 by hand?

I'll get back to you on that one! I think I may have started it once by hand when warm, but can't remember for sure. I can remember failing to start it from cold when I tried once just to find out, and concluded it would definitely need some needs of releasing the decompressor while still turning the handle, but probably also a punishing regime of fitness training!

 

[Mataji]

I was trying to get my head round this last night. If the flywheel is the same weight then I think you would be correct. If the flywheel is of greater mass then it would use that greater mass to start one cylinder (not two) and therefore probs an advantage. Don't know the answer :encouragement:.
Also with a twin , surely if you even get a "spark" on the first compression, you rapidly bring cylinder 2 up to fire whereas on a single it has to go through the whole cycle to catch again.
I am sure I have started twins in the past but never a single Yanmar or Bukh - I am sure I have started a Sabb with the ignition helper.
Anyone started a Bukh DV10 by hand?

The cylinders on the Bukh twin travel together, ie they both compress and reach the top at the same time. Doesn't this make it doubly hard to hand crank?

 

[Poignard]

ll get back to you on that one! I think I may have started it once by hand when warm, but can't remember for sure. I can remember failing to start it from cold when I tried once just to find out, and concluded it would definitely need some needs of releasing the decompressor while still turning the handle, but probably also a punishing regime of fitness training!

Right hand turning the starting handle, left hand operating the decompressor.

 

[Poecheng]

The cylinders on the Bukh twin travel together, ie they both compress and reach the top at the same time. Doesn't this make it doubly hard to hand crank?

Surely they are not both firing at the same time - you only make boxers fire like that? on an in-line twin, they will fire alternately in order better to balance the engine. So even if pistons aligned one is coming up to shove out to the exhaust and the other to ignition ?

 

[rotrax]

I believe that is so with the Bukh twin.

 

[Poecheng]

I believe that is so with the Bukh twin.

Weird. My apologies to Mataji.

 

[neil_s]

I extended the 'handle' end of my Bukh starting handle so that you can get both hands onto it comfortably. Helps a lot!

 

[rotrax]

Good tip-thanks!

 

[chewi]

I believe that is so with the Bukh twin.

why would Bukh do that rather than balance the power by letting the four stroke cycle do it?


surely the pistons rise and fall in sympathy, but the compression cycle.s are 360 degree out of phase.
I bet you have to turn the flywheel to adjust the valves on cyl 2.
That would indicate they are 360 degrees out of phase.

 

[Poecheng]

why would Bukh do that rather than balance the power by letting the four stroke cycle do it?

So you cannot start the bstard by hand !

 

[Mistroma]

I started my old Bukh DV20 a couple of times many years ago. I'm small, light (or was then) and not that strong. Only method that worked was:

1) Disconnect rear decompressor from connecting link on cover and tie it open with a slip knot
2) Tie other decompressor back with a slip knot and length long enough to grip in my mouth
3) Crank furiously with no compression and pull slip knot when at max. speed
4) Release 2nd decompressor once engine firing on one cylinder.
5) Don't forget to reconnect link between decompressors later.

 

[rotrax]

I dont have a Bukh manual but over 50 years of repairing, tuning and modifying WELL out of standard conditions the excellent twin cylinder engines designed by Edward Turner and built in the hundreds of thousands at Meriden by the Triumph Motorcycle Company leads me to believe that Bukh twin engines would have both pistons rising and falling together with one cylinder compressing and firing and the other preparing to do the same next time up.

This is known as a 360 degree twin.

It is possible-and has been done many times-to have both firing together. This effectively makes it a big single cylinder and apart from allowing different pulses to reach the drive train has little merit for anything other than very specific use. Off road motorcycle competition over difficult terrain is one.

The basic problem with a 360 twin is primary balance. The bits whizzing around inside have to be balanced-in the case of a twin cylinder motorcycle by the internal flywheel and the Bukh by the external one. Inertia is a terrible thing inside a high reving motorcycle engine. A piston which weighs 6 ounces at rest will have the effective weight of a fully loaded double decker bus when the poor old con rod has to stop it going up and start it going down at 8,500 RPM in one of my old racing 650cc twins, turning out 64 BHP on a Heenan and Froud water brake.

Those engines did not last long and needed plenty of rebuilds..........................

Another method is the one Honda chose in the early sixties with their 250 and 305cc Super Dream twins-a 180 degree crank.
These had one piston going up and one going down and an offset firing order giving a different exhaust noise. Two stroke twins get away with this very well, but four strokes, due to the cams and cam drives or central flywheels suffer from "rocking couple"-the effect of the crankshaft wanting to rock up and down at the ends due to the uneven balance at low speeds. Get 'em really buzzing-10,000 RPM and above, not a problem.

So, various ways for twins to fire, I am pretty sure the Bukh will be a conventional 360 degree twin with alternate firing order. I think I can tell by the exhaust note.

 

[Vara]

Have started both bukhs and old Volvo two pots from cold, the secret is a second person on the de compressors and easy start, not pretty but it works!

 

[VicMallows]

Have started both bukhs and old Volvo two pots from cold, the secret is a second person on the de compressors and easy start, not pretty but it works!

Totally agree! The problem is that many have been so 'indoctrinated' with the idea that easy-start (ether) will destroy their engine that they would rather call out SeaStart ... or, heaven forbid, the rescue services.