Bukh DV20 Valve Set/Clearence

[Bliss]

Hello everyone.
Im new here. May I ask someone to assist in describing step by step procedure to adjust the valve clearence on a Bukh DV20.

 

[pvb]

Normal procedure - try looking for a YouTube video to show you what's involved in adjusting valve clearances.

Valve clearances with a cold engine are 0.25mm for the inlet valves and 0.30mm for the exhaust valves.

 

[Bliss]

Normal procedure - try looking for a YouTube video to show you what's involved in adjusting valve clearances.

Valve clearances with a cold engine are 0.25mm for the inlet valves and 0.30mm for the exhaust valves.

Hi. Iv tried searching YouTube but I can only find videos on 4,6 and 8 cylinder engines. Is it correct to say that’s it’s not important to find TDC or correct firing order as it appears both pistons fire simultaneously.

 

[PaulRainbow]

Hi. Iv tried searching YouTube but I can only find videos on 4,6 and 8 cylinder engines. Is it correct to say that’s it’s not important to find TDC or correct firing order as it appears both pistons fire simultaneously.

TDC and firing order can be ignored. If one valve on a cylinder is open, the other must be closed, so turn the engine until one valve is open, then adjust the other, same for all cylinders.

 

[Bliss]

TDC and firing order can be ignored. If one valve on a cylinder is open, the other must be closed, so turn the engine until one valve is open, then adjust the other, same for all cylinders.

Many thanks Paul for explaining that to me. Thank you

 

[PeterWright]

Hi. Iv tried searching YouTube but I can only find videos on 4,6 and 8 cylinder engines. Is it correct to say that’s it’s not important to find TDC or correct firing order as it appears both pistons fire simultaneously.

Hi,

I don;t know the engine but both pistons firing simultaneously sounds pretty unlkely to me, unless it's actually designed to shake the boat to pieces.

A 4-stroke twin is normally designed so that the two pistons go up and down together but, on the up stroke one is compressing while the other exhausting and on the down stroke one is firing while the other inducting. For the next revolution, they swap roles. Remember that for a full cycle, a four stroke engine must turn 2 revolutions and that the camshaft turns at half engine speed so that it only turns 1 revolution per cycle.

In general, to set valve clearances you want the follower of the valve you are setting to be on the heel of the cam. To find this position, get the valve wide open then turn the engine 1 rev. This works for all 4 stroke engines, regardless of the number of cylinders.

Peter.

TDC and firing order can be ignored. If one valve on a cylinder is open, the other must be closed, so turn the engine until one valve is open, then adjust the other, same for all cylinders.

Hi paul,

While I agree that it's best to ignore no. of cylinders and firing order, I'm afraid a lot of engines have valve overlap, where the inlet opens before the exhaust closes, hence my preference for the process I described above.
Crude explanation of valve overlap here:

Valve timing - Wikipedia

Peter.

 

[PaulRainbow]

Hi,

I don;t know the engine but both pistons firing simultaneously sounds pretty unlkely to me, unless it's actually designed to shake the boat to pieces.

A 4-stroke twin is normally designed so that the two pistons go up and down together but, on the up stroke one is compressing while the other exhausting and on the down stroke one is firing while the other inducting. For the next revolution, they swap roles. Remember that for a full cycle, a four stroke engine must turn 2 revolutions and that the camshaft turns at half engine speed so that it only turns 1 revolution per cycle.

In general, to set valve clearances you want the follower of the valve you are setting to be on the heel of the cam. To find this position, get the valve wide open then turn the engine 1 rev. This works for all 4 stroke engines, regardless of the number of cylinders.

Peter.

Hi paul,

While I agree that it's best to ignore no. of cylinders and firing order, I'm afraid a lot of engines have valve overlap, where the inlet opens before the exhaust closes, hence my preference for the process I described above.
Crude explanation of valve overlap here:

Valve timing - Wikipedia

Peter.

Hi Peter, i'm aware of valve overlap, but if setting tappets and watching what's happening you'd see that the exhaust valve hadn't fully closed and keep turning the crank until it had closed. Probably easier to just do it, rather than explain it.

 

[Bliss]

Hi,

I don;t know the engine but both pistons firing simultaneously sounds pretty unlkely to me, unless it's actually designed to shake the boat to pieces.

A 4-stroke twin is normally designed so that the two pistons go up and down together but, on the up stroke one is compressing while the other exhausting and on the down stroke one is firing while the other inducting. For the next revolution, they swap roles. Remember that for a full cycle, a four stroke engine must turn 2 revolutions and that the camshaft turns at half engine speed so that it only turns 1 revolution per cycle.

In general, to set valve clearances you want the follower of the valve you are setting to be on the heel of the cam. To find this position, get the valve wide open then turn the engine 1 rev. This works for all 4 stroke engines, regardless of the number of cylinders.

Peter.

Hi paul,

While I agree that it's best to ignore no. of cylinders and firing order, I'm afraid a lot of engines have valve overlap, where the inlet opens before the exhaust closes, hence my preference for the process I described above.
Crude explanation of valve overlap here:

Valve timing - Wikipedia

Peter.

Hi Peter. Sorry I explained it so wrong and probably confused everyone. Probably confused myself more than anything. Lol. Yes both pistons move at the same time. Over the 5 years of owning this fine engine iv been setting the valves totally wrong. Iv been working on the opposite piston after finding position. It actually feels like a different engine no that the valves are in the ball park.Less vibration and a noticeable increase in power are the 2 main things so far. My new method of setting the valves consists of hand rotating the engine, starting with the front cylinder and whilst making sure the exhaust valve is fully in the down(open) position. In this position I then set the intake valve on the same cylinder. After that,I hand rotate again, and whilst making sure the intake valve is in the down(open) position I set the exhaust valve. That’s the first cylinder complete. Then I move onto the other cylinder doing the same procedure. Is this method the correct way of do it. Many thanks for yor taking the time to reply to my post.

 

[PeterWright]

Hi Bliss,

That's Paul's approach, which is OK if you're sure that the open valve is fully open, but you're still quite close to where the one you're trying to set will open. If you use my approach of opening the valve you want to set, then turning the crankshaft one revolution, you will be close to the middle of the heel of that cam and no chance of being on the ramp starting to take up a bit of clearance. That way, even if you get it wrong by + or- 60 degrees, you should still be on the cylindrical part of the cam form. On a Triumph Bonneville with E3134 cams, there is a lot of overlap and the cam forms are very steep so as soon as the exhaust valve just starts to close, the inlet starts to open, but I don't think your Bukh has such aggressive cam geometry.

Peter.

 

[Bliss]

Hi Bliss,

That's Paul's approach, which is OK if you're sure that the open valve is fully open, but you're still quite close to where the one you're trying to set will open. If you use my approach of opening the valve you want to set, then turning the crankshaft one revolution, you will be close to the middle of the heel of that cam and no chance of being on the ramp starting to take up a bit of clearance. That way, even if you get it wrong by + or- 60 degrees, you should still be on the cylindrical part of the cam form. On a Triumph Bonneville with E3134 cams, there is a lot of overlap and the cam forms are very steep so as soon as the exhaust valve just starts to close, the inlet starts to open, but I don't think your Bukh has such aggressive cam geometry.

Peter.

Thanks again Peter for your explanation. I’m truly am learning so much here. I’m currently in the middle of an open sea passage. Should arrive 6pm tonight australia time. When she cools down I plan on fine tuning her using your method. Thanks again.

 

[Bliss]

Hi Peter. Sorry to disturb you. Just wanted to check with you before I start this new improved method of valve adjustment.
Working on the front cylinder I will bring the inlet valve to it’s open position. Then I hand rotate flywheel 1 full revolution and set the exhaust valve on that same front cylinder. Then repeat down the line

 

[ex-Gladys]

Don't forget 360 degree parallel twins the cylinders fire on alternate revolutions... (4 strokes fire each cylinder once every 720 degrees)

 

[pvb]

Don't forget 360 degree parallel twins the cylinders fire on alternate revolutions... (4 strokes fire each cylinder once every 720 degrees)

Forgive me, but is there a difference?

 

[ex-Gladys]

Forgive me, but is there a difference?

Difference from what?

 

[pvb]

Difference from what?

Firing "on alternate revolutions" is surely the same as "once every 720 degrees".

 

[ex-Gladys]

It was an alternative description that may or may not have made it clearer to some readers. Sorry I didn't meet your high linguistic standards.

 

[PeterWright]

Hi Peter. Sorry to disturb you. Just wanted to check with you before I start this new improved method of valve adjustment.
Working on the front cylinder I will bring the inlet valve to it’s open position. Then I hand rotate flywheel 1 full revolution and set the exhaust valve on that same front cylinder. Then repeat down the line

Hi Bliss.

Sorry, I only just picked this up.

The approach I am advocating is that, for anty valve, you rotate the engine until a valve is wide open, you then rotate the crankshaft one full revolution and set that same valve. It doesn;t matter which cylinder or which valve, the same rule applies. If you think, when you rotate the crankshaft one rev, the camshaft turns 1/2 a rev so, if you start on the peak of the cam (valve fully open) you will finish on the heel of the cam.

All the best rules of thumb are simple, reducing the probability of mistakes. This rule of thumb applies to all 4 stroke engines, be they singles, twins V8s or even a Napier Lion H24. No need to add up or take away, just get the valve full open, turn the crank a full turn then set the tappet, all on the same valve. Then you're ready to move on to the next valve.

I like simplicity, probably because I'm a bit simple, but I like to think it's because simplicity is elegant.

Peter.

 

[Bliss]

Hi Bliss.

Sorry, I only just picked this up.

The approach I am advocating is that, for anty valve, you rotate the engine until a valve is wide open, you then rotate the crankshaft one full revolution and set that same valve. It doesn;t matter which cylinder or which valve, the same rule applies. If you think, when you rotate the crankshaft one rev, the camshaft turns 1/2 a rev so, if you start on the peak of the cam (valve fully open) you will finish on the heel of the cam.

All the best rules of thumb are simple, reducing the probability of mistakes. This rule of thumb applies to all 4 stroke engines, be they singles, twins V8s or even a Napier Lion H24. No need to add up or take away, just get the valve full open, turn the crank a full turn then set the tappet, all on the same valve. Then you're ready to move on to the next valve.

I like simplicity, probably because I'm a bit simple, but I like to think it's because simplicity is elegant.

Peter.

Hello again Peter.
This time it has sunk in and thanks for taking the time to provide a well explained procedure. Not have I only corrected my technique but I have a good understanding of what I’m doing. Thanks again, stay safe

 

[PeterWright]

Firing "on alternate revolutions" is surely the same as "once every 720 degrees".

Not in my book. Firing every 720 degrees could be firing on alternate revolutions, but it could be firing on the same revolution if your objective is to induce a lot of vibration, As I said in post #6 above, unlikely, but not impossible.

Peter