1530 valve adjustment

[JonL]

I own a NH 1530. I think NH changed that family (25-33 HP) to the TCs in '99. I looked for TDC(top dead center) in the factory manual and I saw a picture in the fuel pump timing section. When I put #1 cylinder (cylinder at front) close to TDC, I found no mark on the flywheel. I did notice a factory notch with a dab of yellow paint on the back side of the flywheel (just behind the belt) but it did not line up with #1 TDC and the scale on the engine. Am I missing something or doing something wrong?

I guess I could take the injector out of #1 cylinder to find TDC for #1 but I know there must be an easier way. Your help is appreciated.

 

[djradz]

It's been a long time since I did the adjustment on my 1720, but as best I can recall, I didn't worry about finding TDC via the pulley. I think I just rotated the crank (manual says to do it cold) until the valves where closed. Since they're in the closed position for most of the rotation, it gives you plenty of opportunity to make the measurement. You can easily see when the valve goes open and the rocker pushes on it, so I always figured that I just turn it another half a turn (crank rotation) from that point, and it's good to measure.

 

[JonL]

Thanks. That's the method I used. What worried me was the engine characteristics changed a little after the valve adjustment. It idled a bit faster and did not quite have the same wide open RPM. All of my adjustments were adding about .002. That seemed a little odd. I am starting to wonder if my feeler gauge is inaccurate. I have done a lot of valves adjustments on motorcycles in the past so this is not a new thing for me.

 

[Marlowe]

Just a little food for thought here; when adjusting valves on an engine, the piston will reach its top dead center twice during the combustion cycle. The top of the compression stroke is the one you're looking for. That's when both valves should be closed and adjusted. The other time it reaches TDC is the top of the exhaust stroke and the exhaust valve should be closing, or closed, and the intake valve is about to open.

Good luck with it.

Tom

 

[djradz]

Can't say if adding or subtracting is the norm. As the valves wear and seat in further, adding would be necessary. But as the valve steam and rocker surface wear, subtracting would be necessary. You may want to post elsewhere in the forum, to get others' input on this. Sure could see where adjustment could make the engine run different, but I wouldn't have expected top-end speed to be reduced. Good luck. Just a fyi, my 1720 called for 0.008 on both the intake and exhaust.

 

[JonL]

Thanks again. I did double check everything and the valves all appear in spec (.008). The engine had a little over 500 hours on it and this was the first valve adjustment. When I checked the valves, I made sure I was well into the cycle when the valves were closed and made sure the clearances were not measured when the cam had either just closed or was almost opening the valves. I was disappointed not to find a legible TDC mark for #1 cylinder. The small notch on the back of the fly wheel did not line up with TDC of any cylinder that I could tell. Maybe it was for the fuel pump timing.