Questions involving I.P. timing. - Page 4 - PeachParts Mercedes-Benz Forum

winmutt · #46 07-22-2011, 11:01 AM

Quote:

Originally Posted by Stevo

Here is a quote from an old post I have concerning the problem you are refurring to.

"It turns out that a number of IPs made in 1982 were mismarked, so that you actually have to set the driven element so that the wide mark is 3 splines PAST the timing mark. If you've done this, the pump works like any other. This information is clearly set forth in the OM617 engine manual, proving yet again that, even if you know how to do a job, RTFM first."

Ah limited to 1982.

Diesel911 · #47 07-22-2011, 12:49 PM

Quote:

Originally Posted by leathermang

I don't think it is a learning problem.... I think it is an ' avoiding it' problem... several really good threads with pics have been done.. have not looked at them lately... it is really straight forward once you have seen it done... I wonder if Whunter has or would do a video on it.. ? Or anyone else that wanted to... ?

If Hunter did make a Vid He could most likely sell the on eBay for $25-$50. a pop.

leathermang · #48 07-22-2011, 01:23 PM

Quote:

Originally Posted by Harry Verdurchi

Indeed this could be a problem .If the guy did not mark the ballancer to the crank and put it back on 180 degrees off .The crank is offset . Only FOOLPROOF way to check is to pull the Head and put a dial indicator on the top to get TDC then check the Marks . Then you know .

WHOA THERE !!!! The TDC can be determined by pulling a precombustion chamber...
like hundreds of dollars and hours of labor difference!!!!!

Stretch · #49 07-22-2011, 01:30 PM

Quote:

Originally Posted by Harry Verdurchi

Indeed this could be a problem .If the guy did not mark the ballancer to the crank and put it back on 180 degrees off .The crank is offset . Only FOOLPROOF way to check is to pull the Head and put a dial indicator on the top to get TDC then check the Marks . Then you know .

Well I see what you are saying - that would be pretty incompetent. You wouldn't have to remove the head to check though:-

Set the engine with the markings to TDC for number one cylinder. Remove the front group of rocker arms and remove the valve nuts and valve spring on one of the valves on #1 cylinder. Carefully lower the valve onto the top of the piston crown.

If the piston is indeed at TDC the valve will drop by a few millimeters say 6mm.

If the valve stem starts to disappear - quickly pull it back up before it drops into the cylinder... otherwise will need to remove the head to retrieve the valve.

FYI - this is part of the procedure in the FSM for setting up the position of the tachometer sensor on the front of the engine.

leathermang · #50 07-22-2011, 01:35 PM

WHOA THERE ARMY !!!!
That is not good procedure either.... first because you can find TDC by taking out just the precombustion chamber..
AND your method is not the standard and more accurate way of finding TDC... which involves choosing a distance of piston movement before AND after TDC.... having marked those on the crank pulley....you split the difference... THAT is accurate TDC.... because at the top of the stroke.. the actual movement of the piston is non existant for several degrees... thus can not be measured any closer than that that way..

Stretch · #51 07-22-2011, 01:41 PM

Quote:

Originally Posted by leathermang

WHOA THERE ARMY !!!!
That is not good procedure either.... first because you can find TDC by taking out just the precombustion chamber..
AND your method is not the standard and more accurate way of finding TDC... which involves choosing a distance of piston movement before AND after TDC.... having marked those on the crank pulley....you split the difference... THAT is accurate TDC.... because at the top of the stroke.. the actual movement of the piston is non existant for several degrees... thus can not be measured any closer than that that way..

I disagree - if you put a clock gauge (DTI) on the top of the valve stem when doing this you can find TDC very accurately. Have a look at chapter 03-345 in the FSM.

Also for the purpose of the possibility of the timing marks on the end of the crankshaft being 180 degrees out - I'd say it was a very good way of doing it. This valve will either rest on the piston crown or fall into the cylinder (not what you want - so catch it before it falls).

I think this is particularly appropriate for the average home mechanic who is quite unlikely to have the necessary tools to remove the pre-chamber.

leathermang · #52 07-22-2011, 01:49 PM

Think about the physics of the situation I have mentioned....The method I describe as been used for all sorts of engines for decades... you will be SEVERAL degrees off using your method... I don't have to look at the FSM for this one... I have 40 years of messing with engines and the physics is proven...
and taking the front group of rocker arms off... fraught with danger...
As compared to pulling the PCC to put that clock directly on the piston top..

Stretch · #53 07-22-2011, 01:54 PM

Quote:

Originally Posted by leathermang

Think about the physics of the situation I have mentioned....The method I describe as been used for all sorts of engines for decades... you will be SEVERAL degrees off using your method... I don't have to look at the FSM for this one... I have 40 years of messing with engines and the physics is proven...
and taking the front group of rocker arms off... fraught with danger...
As compared to pulling the PCC to put that clock directly on the piston top..

Oh well - it looks like we'll have to agree to disagree on this one. I'd do it my way - and you'd do it yours.

Stevo · #54 07-22-2011, 01:55 PM

Quote:

Originally Posted by tangofox007

Just make sure the manual that you are reading fits the car that you are working on. It's highly unlikely that an OM616 in a '79 240D is going to be fitted with an OM617 IP manufactured in 1982.

Good of you to point that out

leathermang · #55 07-22-2011, 01:56 PM

You are suggesting that pulling the entire head... meaning having to put the chain and everything back together correctly.... is better than having access to the top of the piston ( which is what you are suggesting pulling the head for ) by pulling and reinserting the precombustion chamber ? Think about that first...as your reputation is on the line...

leathermang · #56 07-22-2011, 01:58 PM

Quote:

Originally Posted by Army

Oh well - it looks like we'll have to agree to disagree on this one. I'd do it my way - and you'd do it yours.

Can you not visualize the fact that the movement of the piston is TINY....and for several degrees NOT AT ALL .... when the crank throw is at the top of its rotation cycle ?
Measuring from a distance before... to the same distance after it starts back down and marking the spot half way in between is the standard ACCURATE way to measure it...

Stretch · #57 07-22-2011, 02:02 PM

Quote:

Originally Posted by Harry Verdurchi

I can do it and maybe you and a few others here but as I posted for this fellow for him the ONLY FOOLPROOF WAY for Him would be to do it that way.

If you were planning to remove the head though you could easily perform this simple check.

I'd do this before doing all the extra work.

It isn't quite as good as actually physically checking for the presence of the piston at TDC but it would give you a good idea.

Remove the valve cover and a glow plug on #1 cylinder.

Rotate the crank by hand and watch for the position of the timing marks and the position of the valves over #1 cylinder.

As you rotate the engine you should hear air escaping from the cylinder through the glow plug hole on the compression stroke. The valves should be closed and the timing marks should be more or less in the correct position when the air stops coming out.

Stretch · #58 07-22-2011, 02:12 PM

Quote:

Originally Posted by leathermang

Can you not visualize the fact that the movement of the piston is TINY....and for several degrees NOT AT ALL .... when the crank throw is at the top of its rotation cycle ?
Measuring from a distance before... to the same distance after it starts back down and marking the spot half way in between is the standard ACCURATE way to measure it...

During my winter madness I spent quite a bit of time messing about measuring cam profiles and piston heights - I put quite a bit of information in this thread:-

OM617 (non turbo) cam profile specs, piston height specs etc

When I was measuring the piston height with a DTI I didn't see the dial not moving for several degrees. If I remember correctly it was quite a sudden change as the piston came up the bore, reached TDC and then returned back down. It just goes to show doesn't it? You can never measure too much eh? Now do I need to dig the engine out the back of my garage and prove it to you?

leathermang · #59 07-22-2011, 02:14 PM

No one in their right mind would take the head off one of these engines just to find the top of the piston with the precombustion chamber available.....
Army,
Here is one example.. in this case due to angle he used a method to hard stop the piston and then turned the engine backwards. something our engines do not want to have happen to them due to the long timing chain design... but the phsics are the same...as noted in the second post.. I am not making this stuff up...and it is not a matter of opinion...

http://www.mossmotors.com/forum/forums/thread/5744.aspx

""Finding TDC shouldn't be too hard. First you'll need a degree wheel and some type of pointer. This might be a problem if the engine is in the car, if so then you'll have to be a little less precise but you should still be able to get close. Remove the plugs and make up a piston stop from an old spark plug. I've done this by breaking out the ceramic insulator and drilling and taping the plug body for an appropriate sized bolt. Raise the piston on the number one cylinder to nearly the top, install the piston stop and adjust the bolt until it hits the piston, then lock it in position. Mark the front pully or damper at this point and then carefully turn the engine backwards until the piston hits the stop again. Mark this point. One half way between these two points is TDC. If you're using a degree wheel, then remove the piston stop, rotate the crank to where the calculated TDC lines up with the pointer and mark your damper. If you don't have the degree wheel, then measure between the two marks and mark the center. You should be close enough to be able to set the timing and tune that Prefect.""

""In theory it might work. I'm afraid though that with the piston right at the bottom, a movement of several degrees on the crank would make an all but imperceptible vertical movement of the piston. That's probably pretty much like Bill suggested at the top. Just a very small error in finding the exact top or bottom could lead to a several degree error at the crankshaft."""

Stretch · #60 07-22-2011, 02:29 PM

Quote:

Originally Posted by leathermang

No one in their right mind would take the head off one of these engines just to find the top of the piston with the precombustion chamber available.....
Army,
Here is one example.. in this case due to angle he used a method to hard stop the piston and then turned the engine backwards. something our engines do not want to have happen to them due to the long timing chain design... but the phsics are the same...as noted in the second post.. I am not making this stuff up...and it is not a matter of opinion...

http://www.mossmotors.com/forum/forums/thread/5744.aspx

""Finding TDC shouldn't be too hard. First you'll need a degree wheel and some type of pointer. This might be a problem if the engine is in the car, if so then you'll have to be a little less precise but you should still be able to get close. Remove the plugs and make up a piston stop from an old spark plug. I've done this by breaking out the ceramic insulator and drilling and taping the plug body for an appropriate sized bolt. Raise the piston on the number one cylinder to nearly the top, install the piston stop and adjust the bolt until it hits the piston, then lock it in position. Mark the front pully or damper at this point and then carefully turn the engine backwards until the piston hits the stop again. Mark this point. One half way between these two points is TDC. If you're using a degree wheel, then remove the piston stop, rotate the crank to where the calculated TDC lines up with the pointer and mark your damper. If you don't have the degree wheel, then measure between the two marks and mark the center. You should be close enough to be able to set the timing and tune that Prefect.""

""In theory it might work. I'm afraid though that with the piston right at the bottom, a movement of several degrees on the crank would make an all but imperceptible vertical movement of the piston. That's probably pretty much like Bill suggested at the top. Just a very small error in finding the exact top or bottom could lead to a several degree error at the crankshaft."""

Nice the method in the FSM is similar. However, the FSM method is more accurate as it uses the design of the head with its vertical valve stems and a DTI to do this for us.

I've actually done the head on and head off measurements before. I've already posted a link to the thread for the head on measurements. And here are the head off measurements in this thread

Timing marks gone from my OM617 engine

Here's what I wrote in post #8 many moons ago...

Quote:

Originally Posted by Army

Here are some pictures of setting up and checking the position of the TDC slide. As you can see the head is off - pistons and crank are installed - upper half of the rear crankshaft seal and the front crankshaft seal are in position.

Dial test indicator DTI is used to see when #1 piston reaches end of travel (needle stops moving and starts to head back the way it just came).

There is no adjustment on the pointer bit - just fit it in place - but you can just about see from the picture that there is a hair's breadth of a difference between the zero degree mark on the crankshaft weight and the end of the pointer. Worth remembering!