Test your technical knowledge (for me :-)

[spock500]

Ok, here's the question;

For every two whole revolutions of the crank you have only one compression stoke, the other being to expel the exhaust.

So, on a five cylinder (OM 605) diesel engine how many compression strokes do you have for each single turn assuming No1 cylinder starts at TDC on it's compression stroke?

 

[evdok]

Phone a friend?

 

[Number_Cruncher]

2.5

 

[Dieselman]

ditto NC.
2.5 unless this is a trick question and you lose one due to No1 already being just past it's compression stroke.

 

[Quincy_W140]

Ok, here's the question;

For every two whole revolutions of the crank you have only one compression stoke, the other being to expel the exhaust.

So, on a five cylinder (OM 605) diesel engine how many compression strokes do you have for each single turn assuming No1 cylinder starts at TDC on it's compression stroke?

For every two revolutions of the crankshaft, the camshaft makes 1 revolution.

To answer your question (?) "how many compression strokes do you have for each single turn" [of the crank??]...the answer would be 1/2 as on the first revolution it would be compression and the second exhaust as you stated [or the camshaft??]...the answer would be 1.

Multiply my answer by the number of cylinders.

What are you really trying to work out?

Q.

 

[spock500]

Thanks for the speedy reply chaps -

I have just bolted down the head after having it reconditioned.

Its a bit of a long story but this is the second time due to problems after the first head was refitted it suffered an awful tappet problem.

The first time I re-assembled everything I put the hydraulic tappets onto a radiator for 2/3 to let the oil drain out and then popped them back in - I was told by the head recon centre to put them in a vice with wood and squeeze the oil out which I tried using a large G clamp, it seemed too hard to get the oil out this way so opted for the former.

The engine ran ok but did have this awful tappet noise so I ordered and fitted 20 new lifters - still the same no change, on measuring the gaps from tappet to adjacent tappet there was a large gap (see photo)

So, off comes the head again back to the head centre for another round of grinding and valve stem seals.

I followed the same procedure and put the lifters on a hot rad for a week turning every other day - tons of oil ebbed out onto news paper until they stopped - I have followed the re-assembly to the letter and have ensured everything is torqued up correctly but she wont fire -

Turing the crank over I can only feel compression on maybe one cylinder hence the question of how many compression stokes should you be able to feel per turn -

Ahhh...feel better now thats off my chest

So either there is oil still in the lifters keeping the valves open OR the seats which are now quite deep having been machine twice are causing the valves to protrude too high

 

[Dieselman]

Just check the clearances and perform a leak down test. Even a compression test may reveal valves not closing.
You do have the valve timing correct, don't you.?

 

[spock500]

Yup, valve timing is spot on as left chain on and crank not moved whilst head off -

I dont have a compression test tool but I can only really 'feel' one area of resistance when turning by hand and even this feels a bit weak.

There isnt supposed to be any clearance between the bottom of the lobes and the lifters, should maintain contact all the time to avoid bounce.

 

[Dieselman]

The tappets must have a small amount of slack otherwise they will hold the valves open when hot, or in your case, maybe all the time.

Can you slide a feeler in at all.?

The advice given to compress the tappets before installation was correct.

It seems a silly question, but didn't you check this before installing the head.?

 

[spock500]

I'll take the rocker cover off and try but I doubt it as when I did it the first time you could get a feeler gauge (actually a piece of ally coke can as couldnt find my feeler gauges) under most of the lobes even when the pointy bits were facing upwards.

The only one that you could were those that had a gap (see photo above)

 

[Number_Cruncher]

>>the seats which are now quite deep having been machine twice

I think this is a distinct possibility - the operating range of this type of hydraulic tappet is really quite small.

From the top of the valve stem to the lowest point of the camshaft bearing should be a distance (T) of between 23.7 and 24.2 mm. To measure, take the cams out, put the bearing tops back, and nip down, then rest a round bar along the cam bearings, and measure the gap with some slip gauges.

If you're just outside this range, there is a 0.4mm tolerance on overall valve length, so, you might be able to grind a skim off the tip of the valve stem to bring the T measurement back into range. If you're further out, you'll need to fit new valve seats.

 

[Dieselman]

From the top of the valve stem to the lowest point of the camshaft bearing should be a distance (T) of between 23.7 and 24.2 mm.

Isn't that just the initial spec to check the seats and valves are correct. The hydraulic tappets must have a greater range than that.

 

[spock500]

The hydraulic tappets are very fussy and will not accommodate much at all, those that were sat on the shortened valve stems (see photo) not only were very noisy but let in air whilst expelling most of the oil -

when you took them out you could close them shut in between your fingers and they would spring open again offering no cushion at all

 

[spock500]

>>the seats which are now quite deep having been machine twice

I think this is a distinct possibility - the operating range of this type of hydraulic tappet is really quite small.

From the top of the valve stem to the lowest point of the camshaft bearing should be a distance (T) of between 23.7 and 24.2 mm. To measure, take the cams out, put the bearing tops back, and nip down, then rest a round bar along the cam bearings, and measure the gap with some slip gauges.

If you're just outside this range, there is a 0.4mm tolerance on overall valve length, so, you might be able to grind a skim off the tip of the valve stem to bring the T measurement back into range. If you're further out, you'll need to fit new valve seats.

Let me see if there is much oil left in the lifters, my thoughts are that they may have extended themselves to the maximum limit to accommodate the shorter valves and just putting on the rad wasnt enough, they were also new so could have retained the oil for longer -

I can put them back without any oil in them put the cams back and there should be a gap of some sort do you think?

 

[Number_Cruncher]

>>I can put them back without any oil in them....

If you are taking the hydraulic tappets out, do the measurements as given in my post above (you've already done most of the necessary work!) - it's the only way to be sure that you're in the right range.

Shorter valves?

 

[Number_Cruncher]

>>Isn't that just the initial spec to check the seats and valves are correct.

That's the range given in the MB service information when re-working the cylinder head. The note specifically says;

"If the measurement obtained is less than dimension "T" or "a", it is no longer possible to achieve correct valve clearance compensation; replace valve seat ring or cylinder head as appropriate"

"a" is the depth of the valve rim beneath the plane of the cylinder head sealing surface - I didn't describe it to the OP because it's not a measurement he can easily make with the head installed.

So, in summary, I would take the tolerance seriously.

 

[spock500]

No one is sure what happened but there's a good chance I bent some of the valves by bolting down the cams untimed the first time round causing them to be shorter.

The other possibility that they had been ground too much the first time round, whatever the cause 5/6 of the valves were shorter than those adjacent (see photo) - we have put new valves in to those that were damaged along with new valves guides -

I tend to think it was my fault not paying attention but some of the problems couldnt be explained by this leading to the second conclusion also.

 

[spock500]

Does anyone want a good laff as to what I did to overcome the noisy tappet first time round?

Wasn't going to admit this to anyone but it is funny

 

[Dieselman]

Does anyone want a good laff as to what I did to overcome the noisy tappet first time round?

Not more Coke can...

 

[spock500]

As a 'rule' I wouldn't normally do something like this, but needs must :bannana: