OM615 - head, valves, gasket, and timing chain diagnosis

[kalpol]

I finished getting the head off my 73 220D - now for the thrilling conclusion.

I found No. 3 cylinder 3/4 full of green antifreeze, and found a weird eaten-away shallow place in the head gasket from that cylinder to the water jacket (the outer skin was instact but no gasket in between. The head is not cracked, as far as I can tell, I wiped it up and examined it closely and no cracks do I see. If you'll remember, I noticed timing chain stretch +20 degrees, but there is no evidence the pistons and valves have had inappropriate contact - I examined them very closely and no sort of damage is apparent. However...when I put the head on the ground I noticed a couple of valves stuck open (both exhaust, I think). I poked at them a bit and then tapped them closed with a rubber mallet. I tapped them open with same and all but one closed again. I quit at this point.

So...what is going on here? I can guess at a couple of things: the resistance I felt while turning the engine over was hydraulic lock. The lack of compression is mostly due to valves sticking open. The head gasket is definitely blown between No. 3 and its water jacket and coolant was being sucked in and blown out in large quantities. I have some sticky valves, why I don't know - they are either bent in spite of my inspection or they are all exhaust valves and have sooted up to the point of not working (possible??). The No. 2 and No.3 cylinders look all right but I'll have to look more closely...I noticed two tiny vertical black lines about 10 mm long at the top of No.3. I can't feel anything else in the cylinder and can still see some hone marks I think.

Let me know what you think! Thanks!

[strelnik]

I think you have two choices, depending on your time and motivation:

1. get another identical head and gasket after checking the block surface and the cylinders for wear as much as you can;
2. get lots of little boxes, a a clean work area and disassemble the head cylinder by cylinder, noting everything. If you clean off valves, bolts or other surfaces, DON'T use a steel wire wheel. Use brass on the valves and fasteners, try cleaner on everything else.

Check with a large magnifying class for cracks. If none are seen, consider having the head pressure tested.

Since your engine cannot be sleeved like a 616 can, make sure it's worth the investment before you commit

Get the FSM and take your time.

[Lycoming-8]

Is there something different about the engine in a '73 220D vs a '68 220D? We had the block sleeved on the '68 many years ago, so I would think that it would be possible on a '73 as well.

[JimSmith]

The condition of the head needs to be established after it has been completely disassembled and then cleaned in one of those hot, nasty de-greasing tubs. At that point you can magnetic particle inspect the head (it is not aluminum) and find any cracks. Look carefully in and around the valve seats. Seats can be replaced and minor cracks can be drilled and welded. I had one at the valve seat of two valves and they were successfully repaired, and two new seats were pressed in. On my car the intake valves were the bad ones. They had caked on oily, hard tar from oil leaking past the stem seals and valve guides on the intake side.

The valves should be subjected to the same process and then measured to look for straightness and any unusual wear.

I would replace the guides and springs, as a minimum. Like someone already noted, check the pistons and the cylinders. I was pleasantly surprised on the 1971 220D - the cylinder walls looked like new and piston heads cleaned up nicely.

In those days a local shop did the head work, including the weld repairs and pressing in the valve seats, then machining and lapping all the seats, re-assembling the head, etc, all for $176. The gasket kit cost another $80 or so, meaning for about $250 I had the cylinder head rebuilt and the engine ran like new again. Not sure you can do that for those bucks anymore, but considering inflation you are probably going to come out about on par. Good luck, Jim

[dannym]

Hitting the valves with anything, including a rubber mallet is not a good idea.

You need to remove all the springs and take all the valves out.
Then give the head a good cleaning. A degreasing tub is good but I just use mean green or some other good degreaser. Let it sit for a while and hose it off.

Then the head should be magnetized and sprayed with powder. If there are any cracks you will see them.
If there are cracks you can either fix or replace it. I would replace it. I never heard of fixing a head before. Not saying you can't, just stating my opinion.

Next plane the head to make sure it's flat. Do NOT skip this step!

Clean the valve guides with brass wire brush. It would be a good idea to replace the valves. Coat the shafts with a good moly grease & reinstall.
You should see a big difference on how they move.

Install springs and new valve seals.

Reinstall head with new gasket.

Danny

[jt20]

if you have sticking valves after cleaning the valves throroughly and replacing them into their original guides, you should get new valves and guides.

Unless you are tooled to do so, you probably want a shop to do head work. Simply replacing valves will not do much.

Do not forget the roto caps. The valves are supposed to spin a little each stroke to keep the seat symmetric.

[JimSmith]

The valves are made of a hardened steel. The guides are made of a soft brass or bronze. The guides wear out, the valves don't, unless the seats are damaged, or the engine was run without oil or water or some other out of design parameters condition (like never changing oil). So, the chances are you will need guides. You get the old ones out by either freezing them and knocking them out from the combustion chamber side of the head with a tool, or you just knock them out with the tool. Aluminum heads can be resistant to just knocking them out. This is a cast iron head so it is probably not an issue.

Weld repairing small cracks in cast iron is not all that unusual. Through wall, long cracks is another issue for any essentially finish machined piece like a head. Lots of heat will distort the part and merely truing the parting surface will not correct a bunch of internal twisting and racking. The procedure for small cracks is to drill out the end of the crack to make the intersection between the crack and the sound metal a nice radius, not a sharp corner that forms a stress riser and helps the crack grow. Then you open the crack up a bit for its length and fill the groove and drilled ends in with weld deposited metal. The welder has to be familiar with cast iron to know how much heat is enough to make a sound weld, and how much is too much - too much and the cast iron slumps away from the area, filling in oil and water passages, etc.

On my 220D the valves were all reused. They had well over 150,000 miles on them and were caked with junk when they came out, but they cleaned up fine. The valve seats in the head were another story. Two were cracked and all had to be remachined to re-establish the seating geometry.

All this stuff is within the capability of an automotive machine shop with any experience - they go out of business if they can't do this kind of work well.

Jim

[kalpol]

Originally Posted by JimSmith

On my 220D the valves were all reused. They had well over 150,000 miles on them and were caked with junk when they came out, but they cleaned up fine.

Good information, thanks. How did you clean them? Can they cleaned with a brass brush on a bench grinder, or is that too much?

[JimSmith]

The head disassembly, inspection, cleaning and reassembly was performed by a local machine shop. The valves were cleaned chemically (some kind of hot solvent that does a great job) and then wire brushed to remove anything that was still there, they were inspected for mechanical condition (stem wear, seating surface condition) and then reground to set the seating area geometry. I was expecting to buy new ones and the guy convinced me that was not necessary.

Jim

[Stevo]

Originally Posted by kalpol

Good information, thanks. How did you clean them? Can they cleaned with a brass brush on a bench grinder, or is that too much?

You shouldn't have any trouble with valve guides out and in. I cant remember just exactly what I used as a "tool" but It was something lying around the shop. If you can feel ANY slop in the valves (going through the guides) the guides need to be replaced. I did this job with my mechanic/buddy looking over my shoulder. easy job, be careful putting the springs back, its hard to tell which end goes down.

[JimSmith]

Originally Posted by Stevo

You shouldn't have any trouble with valve guides out and in. I cant remember just exactly what I used as a "tool" but It was something lying around the shop. If you can feel ANY slop in the valves (going through the guides) the guides need to be replaced. I did this job with my mechanic/buddy looking over my shoulder. easy job, be careful putting the springs back, its hard to tell which end goes down.

I presume the new guides were reamed to size before you pressed them in? Anyway, the clearance or play issue between the guides and the valves applies to the new guides. The guides are typically made of softer material, brass or bronze, so they are the part that is designed to wear and be replaced. Not that valves are so costly, it is just good mechanical design practice. So a good valve will rock around a bit in an old guide - and changing the valve instead of the guide is not going to fix the play issue.

The stems should also be measured to determine if they have any taper end to end, or hourglass shape. Anything outside the allowable wear limits in the manual and you should buy replacements. No need to replace all of them, just the ones that are bad. The springs are another story. Harder to examine, more prone to fatigue, so I just changed them.

Good luck, Jim

[Stevo]

"I presume the new guides were reamed to size before you pressed them in? Anyway, the clearance or play issue between the guides and the valves applies to the new guides. The guides are typically made of softer material, brass or bronze, so they are the part that is designed to wear and be replaced. Not that valves are so costly, it is just good mechanical design practice. So a good valve will rock around a bit in an old guide - and changing the valve instead of the guide is not going to fix the play issue.

The stems should also be measured to determine if they have any taper end to end, or hourglass shape. Anything outside the allowable wear limits in the manual and you should buy replacements. No need to replace all of them, just the ones that are bad. The springs are another story. Harder to examine, more prone to fatigue, so I just changed them."

Good luck, Jim
__________________
Jim
I didn't think I said to replace the valves and not the guides We measured the dia of the valves and found them good so they fit into the new guides very nice.
With all due respect, I surely wouldn't get into a pissing contest with you over the proper way to do something on an engine My post was just a comment by a rookie about the job

[JimSmith]

Steve,

I apologize if the tone of my post suggested I was hankering for a pissing contest. I used to write procedures for maintenance on sophisticated equipment and find the total benefit of the information in these threads is often less than the sum of the individual posts - they are, by the process by which the posts are made and certainly not on purpose by the posters, often out of sequence and from different perspectives. My comment was to make sure the guy doing the work did not confuse new valves with old guides as my experience suggests if the mechanic can interpret something the wrong way, he will, eventually. l

So my intent was not to cast aspersions at your contribution, and if that is how it came off, I am sorry. Just trying to make sure the mechanic on this task is not confused by the way threads with information come together. Jim

[Stevo]

Originally Posted by JimSmith

Steve,

I apologize if the tone of my post suggested I was hankering for a pissing contest. I used to write procedures for maintenance on sophisticated equipment and find the total benefit of the information in these threads is often less than the sum of the individual posts - they are, by the process by which the posts are made and certainly not on purpose by the posters, often out of sequence and from different perspectives. My comment was to make sure the guy doing the work did not confuse new valves with old guides as my experience suggests if the mechanic can interpret something the wrong way, he will, eventually. l

So my intent was not to cast aspersions at your contribution, and if that is how it came off, I am sorry. Just trying to make sure the mechanic on this task is not confused by the way threads with information come together. Jim

No apologizing necessary Jim. "tons" can be heard to read, my contributions are usually from the point of view of someone that has made that particular screw up and can feel the posters pain The knowledge and input of the real "Pros" like yourself are the backbone of this form.