OM617 (non turbo) cam profile specs, piston height specs etc - PeachParts Mercedes-Benz Forum

Stretch · #1 12-15-2010, 06:48 AM

G'day Folks,

What with these freezing short days and all (in the Northern hemisphere) I've been messing about making gucci drawings of my new camshaft profile on my 1981 OM617.

I've made some measurements and using a CAD package I've worked out the lift of the cam at 10 degree intervals. I've attached my results in case they are of use to others - may be there is a cam expert out there?

Anyway here's the question - does anyone have an official source for this sort of information?

I'd like to check my measurements.

I've got the latest code 11 cam (successor of the 00 - but probably has the same shape).

layback40 · #2 12-15-2010, 07:05 AM

Interesting piece of work Army.
It doesnt look quite right though.
You will see the sides of the lobe look as though they are approaching being slightly concave. There should be slightly more metal in those regions. The cam that you have drawn would be prone to valve bounce.

I have no idea where you would get the original spec on the cam.

Stretch · #3 12-15-2010, 07:43 AM

Quote:

Originally Posted by layback40

Interesting piece of work Army.
It doesnt look quite right though.
You will see the sides of the lobe look as though they are approaching being slightly concave. There should be slightly more metal in those regions. The cam that you have drawn would be prone to valve bounce.

I have no idea where you would get the original spec on the cam.

Thanks for the response it is a bit rough - I know - I based my drawing on two circles and two tangential lines... the tangential lines start and stop at the same height but their positions are done by eye. So I know it isn't accurate enough.

If I still had the kit I'd use a finely pulsed tachometer and a LVDT to make a time capture measurement of the cam's surface at very slow rotations. But I don't work at a university anymore...

Stretch · #4 12-19-2010, 01:52 PM

I'm going to have to 'do it the old fashioned' way. I'm going to measure the lift from the camshaft with a DTI...

I have found some good graphing software that can interpolate between the measured points for me. I've attached the result set showing the data in the PDF file in my first post.

Strange - I've just noticed that the X-axis values have been decimated - Oh well I'm gonna have to check on that...

panZZer · #5 12-19-2010, 05:28 PM

I was thinking about this yesterday--What if people made a performance cams for the benz like they probably do for the cummins.

DeliveryValve · #6 12-20-2010, 01:36 PM

Quote:

Originally Posted by panZZer

I was thinking about this yesterday--What if people made a performance cams for the benz like they probably do for the cummins.

At the beginning of this year I got in contact with Geoff Bardal at Colt Cams in Aldergrove, British Columbia Canada. I was led to his company through the Volkswagen TDI circle in which he makes a performance TDI profile that people have had good reviews on. He also has done thousands of profiles on various gas and diesel applications and has also done extensive work on the Cummins 5.9L diesel.

I called him to price out a profile for my own TDI. While on the phone, I asked him about a performance profile for the OM617.95x and said he has one that he did back in the 1990’s in which his customer was happy. He has not done one recently, but is experienced in the OM61x since has been to regrind or repaired several to factory specs.

After a little discussion of varying applications the 617 is being used in our circle, he thinks there is a lot of capacity to get more performance out of the 617 cam, even more so then his earlier profile.

He is very interested in the working with 617 folks to create custom grind for each custom use. He offered me for about $340 shipped, a custom grind that he will work with me to get it right, provided that I get him a cam to regrind. I think this a great idea but unfortunately for my engine, I still want to make other mods i.e. different turbo and IP mod.

However, I do think it is important to get some R&D in and if somebody who is further along then I am or is looking to improve on the stock setup, should contact him or even Delta and get a project going. The more profiles available, the better for all of us.

http://www.coltcams.com/

Colt Cams Inc.
2325 264th street
Aldergrove BC V4W 2L5
Canada

Phone: 604-856-3571
Fax: 604-856-3572

.

4x4_Welder · #7 12-19-2010, 10:35 PM

I have had good luck with Delta Camshaft of Tacoma, WA with gasser cams, I'm actually running one of their regrinds in my van right now. It might be worthwhile to contact them and see what they could do with an OM617 cam.

Stretch · #8 12-20-2010, 03:38 AM

I was thinking last night that there is also a bit of a strange relationship between the cam and the cam follower - it slides all over the place. So I'm gonna see if I can measure the movement at the valve as well.

At the moment it is so cold (and humid) here I can't paint my engine bay so I may as well fill in my time with a bit of research.

The operational clearance - the movement of pistons and valves - in these engines is somewhat scary compared with petrol engines.

vstech · #9 01-22-2011, 08:06 AM

ok

Stretch · #10 01-22-2011, 08:13 AM

Quote:

Originally Posted by vstech

ok

Thanks for the thread rename John - it explains a bit more about the content now!

Stretch · #11 02-09-2011, 03:59 AM

Here is data for the position of the cam lobes.

I've only got a 150mm vernier caliper so they are not as good as they could be - there is an accumulative error in the summation of the individual distances for the new cam shaft - the old one I've got worked out better - that was pure luck!

Stretch · #12 11-27-2011, 01:48 PM

...that I'd like to correct.

In post 20 I've got the clearance wrong.

The clearance was measured directly as described in the post.

I measured the "drop" of the valve from its position in the valve seat to the piston crown. This was:-

Inlet (cylinder #1) 3.18mm
Exhaust (cylinder #1) 2.88mm

This is the clearance.

I was trying to find out how thick the head gasket was when fitted... I'm interested in this because the piston on my engine sticks out above the surface of the block by 0.85mm. The head gasket is the only thing that stops disaster!

This roughly drawn picture above is meant to show that the valves are recessed into the head.

In my engine they were:-

Inlet (cylinder #1) 1.05 mm
Exhaust (cylinder #1) 0.8 mm

The recess in the piston crown was measured to be 1.25mm

So adding the distance of the recess in the crown of the piston to the depth at which the valves have been recessed into the head you get

Inlet (cylinder #1) 1.05 mm + 1.25mm = 2.3 mm
Exhaust (cylinder #1) 0.8 mm + 1.25mm = 2.05 mm

So subtracting the combined values of the recesses the distance between the top of the piston and the head is either

Inlet (cylinder #1) 3.18 mm - 2.3 mm = 0.88mm

or

Exhaust (cylinder #1) 2.88 mm - 2.05 mm = 0.83mm

As said before 0.05mm has been "lost" some where in the measuring process. This is equal to the precision of my depth gauge...

So after all that I can estimate my head gasket thickness when fitted to be somewhere between 1.68 mm and 1.73mm on a cold engine! The uncompressed head gasket thickness was 2.2mm.

So a head gasket seems to be compressed by about 20% of its thickness when fitted.

Stretch · #13 11-28-2011, 04:45 AM

I've been wondering about the odd numbers of offset correction for timing chain elongation described in the FSM (chap 5-215). I've done some calculations that suggest that the smallest offset key is pretty useless...

Well it is pretty useless to correct for 4 degrees - it is better for 6!

Take a look at this image of the PDF I've attached.

The diameter of the hole in the camshaft sprocket on my OM617 non turbo is most definitely 28mm - but it looks like Mercedes have designed the offset keys for a 30mm diameter. Does anyone know if the turbo cam has a 30mm diameter hole in the camshaft sprocket?

And the size of the Woodruff key / offset key slot is 4mm

I've measured the PCD of the camshaft sprocket and I reckon it is 119mm. I've used this value to calculate the circumference of a "circle" running around the sprocket where I expect the chain to be resting. This circumference was then proportionally divided up for each angle of elongation => i.e. circumference of PCD circle divided by 360 degrees multiplied by "degree of elongation at camshaft sprocket"

It is nice to see that roughly speaking if you have one degree of elongation measured at the crank that is equivalent to about 0.5mm linear elongation.