617 piston/valve clearance - PeachParts Mercedes-Benz Forum

4x4_Welder · #1 01-12-2011, 09:38 PM

I am talking with the guys at Delta cams about a performance cam for the 617, but need to know what the clearance is between the valves and pistons at TDC. As I do not have my engine disassembled right now, does anyone else have this spec?

t walgamuth · #2 01-12-2011, 10:17 PM

Not very much. Why would it matter? at TDC, by definition, the valves are closed.

leathermang · #3 01-12-2011, 10:23 PM

Quote:

Originally Posted by 4x4_Welder

performance cam for the 617

4x4_Welder · #4 01-13-2011, 12:38 AM

Hey, I'm trying. Clearance is important for timing and overlap at intake/exhaust TDC, when both valves are slightly open.
Most of the power increases over the production of these engines were due to changes in the cam profile. I see lots of people talking more fuel, more boost, and no cam alterations so it's an overlooked part. I know going to a Delta torque grind in my Subaru EA81 actually really woke it up, I am also running a Delta custom grind in the 300 in my van with great results.

DeliveryValve · #5 01-13-2011, 12:45 AM

Quote:

Originally Posted by 4x4_Welder

Hey, I'm trying. Clearance is important for timing and overlap at intake/exhaust TDC, when both valves are slightly open......

If Delta doesn't have that info, then why reinvent the wheel when Colt Cams has that info and is already set up for a performance grind?

coltcams.com

.

leathermang · #6 01-13-2011, 01:04 AM

Quote:

Originally Posted by 4x4_Welder

Subaru EA81

I love that engine.. it will really perk up with the Redline Weber 32/36 carb on it. That is a pushrod engine used by many experimental aircraft people due to being ' bulletproof'... It is the VW air cooled 4 engine with the 7 major faults fixed.. due to the hiring of the former head of VW. It is smaller and lighter than the air cooled engine with twice the hp stock... meaning AC can be run on it down here in the south.

gastropodus · #7 01-13-2011, 01:16 AM

Quote:

Originally Posted by leathermang

I love that engine.. it will really perk up with the Redline Weber 32/36 carb on it. That is a pushrod engine used by many experimental aircraft people due to being ' bulletproof'... It is the VW air cooled 4 engine with the 7 major faults fixed.. due to the hiring of the former head of VW. It is smaller and lighter than the air cooled engine with twice the hp stock... meaning AC can be run on it down here in the south.

Off-topic, but curious... what are the seven major faults? I know one big one was VW putting the dog house oil cooler behind piston #3, making it run hotter.

Kurt

leathermang · #8 01-13-2011, 01:31 AM

Screw on paper oil filter instead of just wire screen in bottom of pan, Water cooled, electronic ignition, available with hydraulic lifters, more compact and lighter..not needing the heat exchangers used for providing warm air to passengers, Not a single bolt holding the flywheel on, 15,000 mile valve setting instead of 1000 ( Muir recommendation). Alternator.Screw on valve cover holding instead of that over the center wire spring.

Stretch · #9 01-13-2011, 04:56 AM

Quote:

Originally Posted by 4x4_Welder

I am talking with the guys at Delta cams about a performance cam for the 617, but need to know what the clearance is between the valves and pistons at TDC. As I do not have my engine disassembled right now, does anyone else have this spec?

Errr as stated above at TDC the valves are shut - very shut.

The pistons on my (non-turbo) OM617 protrude from the block by about 1.6mm if I remember correctly. Check the FSM for the limits.

The valves sit in the head - just below the surface. I think they can be recessed by about 1.5mm from the surface. Again check the FSM as I'm doing these numbers from memory.

The only thing that stops the pistons from hitting the head is the head gasket. I measured my new head gasket to be 2.2mm when it is uncompressed. I forgot to measure the old head gasket - if I find it (though I may have chucked it already) I'll measure that thickness too.

If you want to see a measurement of the cam surfaces on both the inlet and outlet valves for #1 cylinder on my engine you can see that here:-

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

t walgamuth · #10 01-13-2011, 05:22 AM

Ok now I realized it. Of course overlap occurs when the piston is up on the exhaust stroke.

I doubt there is much room to increase lift at this point in the cycle though. There is just not much room in the combustion chamber to work with.

barry123400 · #11 01-13-2011, 10:36 AM

Increasing lift is not practical I would think. Duration increases are limited as well I suspect to less than eighteen degrees on either side of TDC. This is because the engine becomes an interference engine when the cam is only eighteen degrees off. My logic may be fuzzy here so make allowances.

As the revs come up floating valves may also be another problem but with good valve springs and the engine rpm not elevated much it may not be an issue.

I would try to locate a company that has actually got the specs of the redesign of the original cam profile and has proven it in service. Not start from scratch.

The suggestion to contact colt cams is the way to go in my opinion as well. If they post their reprofile changes it would be nice if you could post them on site and the claimed difference. Most engines out there intake fuel through the intake valve.

Unfortunatly these old indirect diesel intake fuel from the precombustion chamber so I would thing there may be something to gain but not as much as on a typical gas engine. In the final anyalisis what do I know though? Colt cams claims might blow me out of the water.

Now the above said the later cams over the earlier are a higher horsepower gain type I believe in the 123 blocks. I guess the issue is if the factory did take it as far as practical.

leathermang · #12 01-13-2011, 12:40 PM

I agree with these last three answers.

If someone was to look for an aftermarket cam.... they should study the FSM concerning the cautions listed as to matching the cam and the follower.. or something that contacts it... as some I think are ' chilled' some hardened' or some combo.. just a warning... would not want to do all that work and then just have one part eat up the other one due to metallurgical ignorance.

And I still say... if you want more hp get another type of car... if you want longevity and fuel efficiency along with good looks... do normal preventive maintenance to your car.

Alastair · #13 01-13-2011, 01:28 PM

Best way is measure it....

Shove a dial-gauge on each valve at TDC Firing-stroke, then press down the valve by levering it down into contact with piston and measure the movement indicated on the dial gauge...

The Valves are recessed into the head, usually well below the face due to wear...(Ive seen up to 1.5mm below head face on an old engine with original valves and seats)

There are Valve Cut-Outs in the Pistons of approximately 1mm on my N/A engines....

As most of these engines are 30+ years old, the valve-seats in the head will be worn down increasing clearances....
--Maybe the engine you are thinking of modding also has 30 year old valves as well, increasing clearances even more!

--Obviously all the above should be back to 'Spec' if the head has been Properly Re-Manufactured with new Seats and Valves etc--(But--How often is This done)

...

I'll bet you'll be surprised just how much clearance you'll find if its measured....

As a limit, they say the clearance between valve and piston should never be made below 20 thou, if you're grinding heads messing with valves or timing or messing with head-gasket thicknesses, Same would apply for 'overlap lift' ....

4x4_Welder · #14 01-13-2011, 01:33 PM

It's more the timing of the intake/exhaust valve opening, including overlap that can really make a difference in the engine. Advancing the cam you could get a Cummins-like powerband, retard it and it'll have plenty of horsepower but only at higher rpms. Too much overlap and it won't be able to build boost, too little and it won't scavenge properly, the list goes on and on.
I just think there is a lot of potential left in these engines, and the Fins have proven it.
Oh yeah, I already have gotten rid of the car. I have made a highly disapproved use of putting it in a truck. I can't leave anything alone.

leathermang · #15 01-13-2011, 01:41 PM

I do not disapprove of you putting it into something else.... I assume YOU OWNED both of the vehicles .. LOL
I probably missed it... but tell us about the ' FINS' finding the rest of the potential of this engine.... The more sophisticated engine you start with.. the harder it is to make gains...
and we are assuming those gains are not at the expense of Longevity....