I.H. 606 problem

Hi guys - I am an old school diesel injection guy originally from UK now living in New Zealand. I am trying to help an old tractor enthusiast friend of mine ( he has no Internet) with a problem. This is it in a nutshell.

We have a 1960’s International 606 Tractor with a D236 engine.

It idles perfectly at 600-650 rpm. When the throttle is opened there is a knocking sound (similar to “diesel knock”) for about 2 to 3 seconds then by the time the engine has reached 1000rpm the noise completely disappears and the engine runs beautifully at all speeds. I haven’t actually heard it myself but the owner says he thinks he can hear the noise through the inlet manifold. We are pretty certain the noise is not caused by the injector nozzles as they are all new plus there is no smoke of any sort when the knock occurs. The owner says it is just annoying really rather than being a major problem but he would like to get to the bottom of it – and so would I !! There is a possibility that the guy who re-worked the cylinder head has used brass or bronze valve guides – could this be anything to do with it do you think?
Any thoughts would be much appreciated.
Cheers
Rod

I would check two things, maybe three. First off, static timing. It should be 3 degrees BTDC. If that checks ok and it runs good at full throttle, no sputter I would go to third check and that is valve clearance of .027 all around. If the static timing is earlier than 3, I would retard it to correct and then put a window on and check the automatic load advance. A whole lot of guys, have a sputtering engine at high speeds, no load and they advance the timing to get rid of it when in reality they need to look at the load advance. That engine should have zero advance while cranking and as soon as the engine starts it should advance two marks on window. It needs to be set under load on a dynamometer so it maintains full advance at all no load speeds but retards one mark at half load and retards two marks at full load. I have set many over the years by just making sure the retard some while accelerating from low idle to full throttle. That for sure is not the best way but it will get you by. I also have seen an engine where the valves were protruding a little too much and touching the pistons. I didn't notice a knock though. Most of the time the valves are recessed too much but some machine shops push the height in head a little too much.

Thank you very much Pete - I have passed this on. Much appreciated!