crankshaft and camshaft

[EASLOOP]

My East Anglian has an ageing Bukh DV10 diesel. I am having major problems starting. Bukh have been exceptionally helpful but I want to know if anyone else has had a problem similar to that which follows. I have been unable to start the engine following a head re-build. When the exhaust valve seized the push rod hit probably the rocker arm and bent. This may have caused the camshaft to be shifted out of sync with the crankshft. Apparantly up to about 1975 - date of my engine - the cams were sweated onto the shaft. But following such problems the cams were sweated and pinned. Bukh advise me to check the alignment of the two shafts by use of some very special kit that I do not have nor know how to use. They have a pragmatic check which involves looking at the rocker arms movement and the TDC position etc.
Has anyone ever had this problem? and if so how did you discover it and solve it.
Looking forward to some input. I may have to learn to sail off and onto the moorings.

John
Otty Bird

 

[aztec]

is TDC marked on your flywheel/pulley?

if it is then you should find both inlet and exhaust valves "overlapping" by a simmilar amount. (meaning they should both be open slightly at TDC on ecxhaust stroke or "rocking"... both have clearance on power stroke)

if one is different to the other your diagnosis may be right.

the camshaft will be timed to the crank position, it sounds like there is a possibility of the exhaust lobe having moved (never heard of this though) in which case you'll need to replace the camshaft. or the camshaft has moved (jumped a tooth/teeth) in which case wear must be present.

looking from a different angle;

did the exhaust valve "sieze" and why??, or did the cam cause it to impact the piston?

just a thought.

hope you find the answer.

steve.

 

[EASLOOP]

Hi,
Thanks fery much for your input.

On removing the cylinder head I saw that the exhaust valve was coked up along parts of the distal end of the valve shaft. The valve surfaces were badly corroded and was no doubt leaking. The exh valve was jammed in the guide to the fully opened position, i.e. as far as the rocker could push the pushrod without hitting the piston. I think the following is what happend. When the valve jammed fully opened on the next stroke the rocker arm had nothing to stablize it and so flopped around. As the pushrod, having flopped to one side and now out of aligment with the tappet - came up with the cam the pushrod cup edge caught the tappet adjuster and jammed into the rocker bending the rod. This only occurred with the exhaust valve, the inlet was OK and its pushrod was not bent. With a re-furbed head installed - complete with new valves, guides, etc etc, - I can bring the piston to what I think is TDC (good compression) at which point both valves are closed with tappet clearance. As both valves are synchronised it seems that both cams are either OK or both have been moved.

I am not familiar with 'rocking' and 'overlapping'. Could you put it in words I can understand? i would like to be able to check this tommorow.

rgds
John

 

[rogerthebodger]

The best way to check cam shaft /crank shaft alignment is not at TDC on the compression stroke but at TDC on the exhaust stroke.

On the compression stroke both valves are closes for most of the up stroke but at TDC on the exhaust up strike the inlet valve is just starting to open and the exhaust valve is just finishing closing and as you move the crank back and forth you will see the valves both move and can determin there position better than on the compression stroke

 

[boatmike]

It sounds as if your head has been refurbished OK but in replacing it you have the valve timing wrong. As you already have advice from Bukh you should have some sort of timing diagram. The check your other correspondent suggests is not precise enough frankly. You need to see when exhaust and inlet valves open and close relative to TDC and then use a protractor to mark these points on your flywheel. Then rotating the engine (in the correct direction!) and watching the rockers should make it obvious if you are one tooth out on timing. If unsure I strongly recommend find a good diesel mechanic to check it for you or you could end up with bent valves again or worse.

 

[aztec]

ok, sounds as if the cause of the problem was the valve then. i would also tend to think that the damage to the valvetrain would take some of the load off of the camshaft.


right before you get too involved in the cam timing issue, recheck everything else including fueling. after the pump/injector has been disturbed make sure that fuel is actually getting there. all a diesel needs is hot air (compression) and fuel and it should at least fire/smoke. are you getting anything from the motor?

it sounds as though you have compression, so i'd be looking at the fuel side first.

has the cam been out?, and has the injection pump been removed/moved?

 

[EASLOOP]

Hi,
Thanks for your help. I have had my injector completely rebuilt by a very competent engineer - all for only £40. I saw the unit as it was disassembled and it is a complete wonder why it worked at all - but it did!
Installing the injector tomorrow - work permitting - and wll see what happens.

I'll let you know the outcome.
rgds
John

 

[Heckler]

when the piston comes to top dead centre the valves are both closed on one stroke (the firing stroke) and on the next TDC the valves should be "on the rock" i.e as the piston gets to TDC one valve will be closing as it gets to the top and as it goes past the top the other valve will start to open, hence the saying "on the rock" you can twist the crankshaft pulley back and forward before TDC and after TDC and as you do so the valves appear to rock.