OM617 (non turbo) cam profile specs, piston height specs etc - Page 2 - PeachParts Mercedes-Benz Forum

DeliveryValve · #16 12-20-2010, 08:25 PM

Quote:

Originally Posted by panZZer

Where does one get a blank?? you need MORE material for higher lift ,not regrinding one that was already ground, all you could do is play with the ramps with a used cam.

A cam is basically a bump on a circle. When the follower is siding on the circle, it is at zero lift. As the cam rotates, the follower goes over the bump positive lift is created. When you regrind a used cam, you make the circle smaller so the bump would have a higher lift. The valves are then adjusted to take up the slack from making the circle smaller. But there is a cut off point to how much it can be adjusted and custom adjusters may have to be created.

Lift is just one aspect of a few aspects to consider in cam grinding, the art is to find the right amount to make the engine happy. Some other aspects to consider are lob separation, overlap, duration and lobe centerline.

Of course IF your engine calls for a much higher lift, then a blank cam maybe in order. But you have to remember with the higher the lift, it may also entail having a reliefs cut in the pistons from keeping the valves from hitting them.

You might want to talk to Geoff in person, he is very approachable and will talk to you through on what he can do with a used cam that's not worn.
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Stretch · #17 12-21-2010, 04:46 AM

Quote:

Originally Posted by DeliveryValve

I doubt it, these cam companies like to keep everything secret. You know... they would like to make money...

.

I understand that for custom cams the data might be considered to be more sensitive - although just like the bomb you can't de-invent it and it can be copied - even so I was wondering about the stock / original version.

It would be nice to get confirmation of the bench mark dimensions that I will be measuring and publishing here!

Stretch · #18 12-29-2010, 09:09 AM

I've persuaded the wife to let me work indoors so long as I keep the place clean - it is way too cold for this fair weather mechanic to work in his garage... so here are some more measurements of my new camshaft. When it gets warmer perhaps I'll even fit it to the engine - you never know!

I've used the camshaft cog as a reference point for the camshaft position. I've loosely assembled the camshaft in the bearing towers on the living room table and positioned a clock gauge (DTI) on a stand so I can measure the cam rise. I plan to repeat this measurement when the camshaft is positioned in the engine as I expect I'll get more consistent results.

I defined tooth number one as the TDC tooth when the camshaft alignment marks are set correctly for the correct timing - also top dead centre - but I've measured the top of the cam surface NOT the point at which the cam touches the cam follower. See picture. The measurement of the cam height is approximately 11 teeth behind the point of cam / cam follower contact. I'm going to check this out too.

From the measurements and the data in the FSM you can see that this cam (code 11) is a normal power cam for a normally aspirated OM617. The lift is 8.5mm not like the uprated cam which has a 10mm intake lift and a 10.4mm exhaust lift.

Stretch · #19 01-18-2011, 03:26 PM

well you might be interested in piston height?

Stretch · #20 01-22-2011, 06:24 AM

I thought the following measurement might be of use to those of you who are interested in cams and perhaps modifying them: A measurement of the clearance between the piston at TDC and the valves.

To measure this I did the following:-

1) Set the crank to TDC by aligning the marks on the balancer and the timing pointer.

2) Moved the camshaft out of the way - I'm in the middle of rebuilding my engine so this was easy for me as the timing chain wasn't even set up!

3) Removed the valve nuts and springs and allowed one of the valves to slide down onto the piston crown.

4) Set up a clock gauge / DTI and adjusted the position of the crankshaft so that the dial gauge was at its highest point - i.e. I checked the piston was actually at TDC

5) Pulled the valve up - measured - pushed the valve down - measured

Here are the results:-

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

I had previously checked the valve depths on the head (during my rebuild) and these were 1.05mm (inlet) and 0.8mm (exhaust)

So the measured clearance between the recesses in the piston and the valve is:-

Inlet (Piston #1) 2.13mm
Exhaust (Piston #1) 2.08mm

The difference of 0.05mm between the two measurements can be attributed to the precision of my depth gauge (0.05mm) and the castings on the piston crowns - and any errors I made such as not having the DTI exactly upright - it looks terrible in the photo above!

vstech · #21 01-22-2011, 08:06 AM

ok

Stretch · #22 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 · #23 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 · #24 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 · #25 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.

Stretch · #26 11-28-2011, 02:12 PM

...the difference between the calculations and the data in the FSM?