Engine timing - TDC

[Tomo23]

I've had the pump done up for an om366 unimog engine. we've had it running but this mog has had some serious money on it so I want to get it spot on.
Ive been advised about how to do the timing etc but to find true TDC I've been told to drop a valve and use a dial gauge.
That in itself I'm happy with.
But how do I hold the valve up and compress the spring to get the collets back in when I'm sorted?

 

[Phil P]

I’m not familiar with that particular engine but on the one’s I’ve done the piston will hold the valve up enough to get the spring back on. It depends on whether it’s a flat top head and the shape of the piston though.
If the piston won’t hold the valve up enough another way is to remove the heater plug or an injector then use and airline to put pressure into the cylinder and hold the valves closed.

 

[Tomo23]

I had heard of the air trick but thought if I've got to have an injector out I could just put something down that hole with the dial gauge and save dropping a valve in the first place.

My dad did say the piston could hold the valve up. He had also read that there is enough adjustment on the tappet to push the valve onto the piston and just use the dial gauge on the rocker arm. Or something to that effect.

 

[Phil P]

I had heard of the air trick but thought if I've got to have an injector out I could just put something down that hole with the dial gauge and save dropping a valve in the first place.

My dad did say the piston could hold the valve up. He had also read that there is enough adjustment on the tappet to push the valve onto the piston and just use the dial gauge on the rocker arm. Or something to that effect.

I wouldn’t tighten the rocker down as you could end up bending something if it goes tight!

 

[ACEngineering]

I've had the pump done up for an om366 unimog engine. we've had it running but this mog has had some serious money on it so I want to get it spot on.
Ive been advised about how to do the timing etc but to find true TDC I've been told to drop a valve and use a dial gauge.
That in itself I'm happy with.
But how do I hold the valve up and compress the spring to get the collets back in when I'm sorted?

Dropping valve is best way I find on a perky.
They dont drop much when on TDC due to the piston.

Just make sure you dont turn engine too far and loose it inside

 

[Tomo23]

I wouldn’t tighten the rocker down as you could end up bending something if it goes tight!

That was my worry.

Dropping valve is best way I find on a perky.
They dont drop much when on TDC due to the piston.

Just make sure you dont turn engine too far and loose it inside

Crikey don't say that.

 

[Pennine Ploughing]

Best way is to bolt a long bar on a pivot over the valve head, and hang enough weights on it to open the valve to make it touch the piston, i made one out of a breaker bar, get an old socket welded horizontal to a plate with holes in it, make a leg with holes in it, bolt or clamp the leg to the head, , bolt together at appropriate hight, put in long breaker bar, hang weights on it to it opens the valve, on to piston, dial gauge on and rock the crank at tdc
Saves dropping a valve and danger of it dropping in if turn over

 

[Tomo23]

Best way is to bolt a long bar on a pivot over the valve head, and hang enough weights on it to open the valve to make it touch the piston, i made one out of a breaker bar, get an old socket welded horizontal to a plate with holes in it, make a leg with holes in it, bolt or clamp the leg to the head, , bolt together at appropriate hight, put in long breaker bar, hang weights on it to it opens the valve, on to piston, dial gauge on and rock the crank at tdc
Saves dropping a valve and danger of it dropping in if turn over

Now I like that idea. I think I might just have enough room to the side to get away with that.

 

[davidroberts30]

the problem is not holding the valve up but compressing the spring

bit of chain on a rocker bolt and a spring compressor on that
but best way is as said just lever the whole valve and spring down and dial on top of that

 

[Tomo23]

Quick setup made up and used a dial Vernier caliper as a gauge.

 

[pail of ale]

U sure there isnt a mark on the front pulley

 

[Tomo23]

U sure there isnt a mark on the front pulley

It looked more like a big gouge mark. We wanted to be sure.

 

[William james]

Small tight o ring onto the valve stem to stop it dropping fully down?

 

[MrNoo]

U sure there isnt a mark on the front pulley

Trouble is they are not always right, I always (when rebuilding an engine) put a dial gauge on to find TDC before I whack the head on, surprising how many are not right. I have done them before through the injector port but not the best way.