Valve clearance at zero

[Sokoloff]

This spring I as I was adjusting my valves, I found that #3 exhaust was at zero, i.e. no clearance at all. Thought maybe it was operator error. :) I'm good at that. So I adjusted the valves and checked it again about a month later after a couple of hundred miles. It was 0.21mm. Spec. is 0.20, so I figured maybe I was okay.

But today I just adjusted the valves again. #3 exhaust was again at zero. #4 exhaust was at 0.08 and #5 exhaust was at 0.30. All others were still pretty close to spec.

My compression numbers this spring were
1 150

2 135

3 128

4 115

5 135

6 150

A wet compression test was suggested and that's what I was planning on doing over Christmas when my son came home. That's why I was adjusting my valves in the first place.



So, any ideas what I'm looking at here? As far as I know, this engine has never been opened up, but has the time come for a valve job?



Len

[bill streep]

Len, I'm sure you've been over this - but, here goes:

When you measured your valves, where was the measurement taken (cam to rocker, or valve stem to rocker), as it's different for different cars. If it's at the valve stem as my 190SL is, it can be real difficult to slide the gauge in between the stem and the rocker - and it seems to go from zero to spec with just barely a turn... You could "cheat", get the right spec on one of them, then measure the rocker/cam clearance and use it for the others.

Also, take a look at your adjusting screws. SOMETIMES the nuts get wacked with the cam lobe, and this can really screw things up. If you are measuring lobe to rocker, as I recollect, it's supposed to be done with the lobe at 90 degrees. On older cars, the lobes can be off a bit...

As you probably know, it's most important to have valve clearances that are similar, AND that all have some clearance - to keep the pistons from wacking the valves.

As for compression, again consistancy is key. #4 is bothersome. Try the old squirt of 30W in the spark plug hole and then check compression. If it doesn't improve, it's usually top end. But I'm thinking you know this... I'm writing this for those that follow...

If it's top end, I'd run some Techron or other top end cleaning product thru before tearing it apart. You never know...

BTW, what model is this? I forget.

[Sokoloff]

Sorry, Bill, It's a '59 220S cabrolet I'm talking about here. Thought I had that in my signature block, but left it out. Assume nothing with me. :) I've done a lot of work on the outside of my engine, but have never opened one up. I've never done or diagnosed a valve job, so all suggestions/help are appreciated.

[bill streep]

Len, the book says .008 for Exhaust, .005 for Intake. Measured between the bottom of adjusting screw on the rocker, and the top of the valve. Don't have the compression handy. Make SURE your lock nuts are on tight - and as I noted above, it's REAL easy for these to screw up. May also need new adjusting screws - they tend to wear.

[Sokoloff]

I was talking metric, .12mm for intake, .20mm for exhaust. I'd sure love the problem to be something simple like worn screws/nuts. The engine has about 75,000 original miles on it and has never been opened as far as I know.

Len

[ja17]

Hello Len,
The compression for a particular engine is often cast into the cylinder head right below the head part number. These numbers are on the spark plug side of the head. The compresson will be in atmospheres probably 7.6 or 8.7 directly under the head number. Multiply this figure by 14.7 for the correct compression in psi. This type of valve train will wear tight, in other words the valves become tighter over a period of time. If this happens too soon you may have a problem. Bill has given much good insight on some possibilities here. If the valve continues to tighten up, it may be deteriorating and you will notice the compression falling off on that particular cylinder hot or cold wet or dry. Ring problems will usually leave hard crusty deposites on the spark plugs and oil consumption can be an issue. Read your spark plugs for more hints.
My first impression on seeing your compression figures is that a previous owner may have overheated the engine and warped the head at some point. When the head warps, it arches in the middle and the head gasket lets go. The common fix is for a machine shop to cut or mill the head. With the head being arched, more material is removed from the front and rear combustion chambers causing the compression to be noticably higher in the end cylinders, (as noted with your compression readings). Ideally the compression variation between the highest and lowest cylinders should be no more than 10%. Larger variation may cause a little roughness in idle or some problems with timing. This may not be fatal, but some compromises in smoothness and performance can result. This is just one possibility for your wide range of compression figures.

More observation and information needed. Keep an eye on the valve that keeps getting tight. If it is deteriorating it will continue getting tight and the compression will begin dropping off. If so it will reach a point at which you will have a noticable miss at idle on the bad cylinder and a decrease in power will be noticable.
Be sure to measure vavle adjustment in the correct place as Bill stated. Remember loose valves will make a little noise but tight valves will burn eventually! Keep us informed.

Joe Alexander
Blacklick, Ohio

[Sokoloff]

Thanks for the reply Joe. I'll try to pull the spark plugs tomorrow if I get a chance. I did pull them earlier this year some time after the first incident of a zero valve clearance. They all looked good. Oil usage has gone up slightly this year. Compression is 8.7:1. Car runs very well.

As for overheating, I can't say that it has never happened. I have owned the car since 44,000 miles. 77,000 miles on it now. No evidence of any head gasket problems that I've noticed. Wouldn't an overheating usually show up as a head gasket/oil/coolant problem? Oh, upon rereading your post, you meant that it may have had a head gasket problem repaired once.

Len

[ja17]

Hello Len,
I am only saying the past history of that cylinder head is a little suspicious with your compression readings like they are. Some of your compression readings are actually higher than specs and others lower. We have no way of knowing for sure unless you have the repair records from the previous owner.
Watch for any decreasing compression in that #3 cylinder which may indicate a bunt valve.
The fact that it runs very well is a good sign. Maybe the adjustment will settle in and be ok. 77,000 miles is not a lot for one of these engines. Good luck!

Joe Alexander
Blacklick, Ohio

[john m]

Hello sokoloff
My general rule; three valve adjustments; then install new nuts.
Since you are not the original owner; replace the nuts now.

I would suggest making friends with a good local mechanic; an invitation to your house and an adult beverage or three can do wonders.
If you just happen to have the valve covers off and ready to adjust; "well", what true mechanic can resist tinkering or showing off to an amateur? :)

[Sokoloff]

What are you drinking John? :)
See attached photo of the plugs. #3 is a bit darker than the others. Other than that, they all look okay.

Len

[Sokoloff]

Did another compression test today, including wet on the two low cylinders. Here are the results:

1 90 149

2 89 142

3 85 135 wet 90 162

4 75 120 wet 90 146

5 85 138

6 90 150

Since the compression came up so much with the wet test, the problem probably isn't with the valve and the seat being burned but rather something with the adjusting nut/screw. The plan is to swap the adjusting screw with the valves that are holding the clearance and see what happens. Plans are also to get all new lock nuts.

Other input welcomed.

Len

[Sokoloff]

The first number in my compression test is the initial number that the compression gauge jumps to.

Len

[ja17]

Hello Len,
Anything which takes up space in the combustion chambers will raise the compression. So if you squirted a lot of oil in the cylinders, you will get a false reading. Just a little to seal things up is the norm.

The spark plugs look good. I always had good luck with the NGK plugs also.

The valve adjustment will not normally make much difference in compression as long as the valves close. The ends of the adjuster screw (tappet), are normally what gets worn, causing adjustment to be difficult. These hardened ends get worn like the facets of a cut diamond instead of being round and smooth.
The bronze bushings on the shaft ends of the rocker arms wear as well as the rocker arm shafts themselves. All these things contribute to the valves not staying in perfect adjustment. A lot of expensive parts here however as long as the valves close your compression should be nearly optimal.

If you have bottom end problems, which I doubt, (at 77,000 mi.) you will have oil or oil deposits showing up on your spark plugs. This does not seam to be the case. Is your mileage documented to be correct? How long were those plugs in the car? Are you checking the compression when the engine is warm?

Joe Alexander
Blacklick, Ohio

[Bambo Jr.]

I had low 90# compression in #5 cylinder and a second compression check after squirting oil in raised it to 140#. I assumed I had a broken or stuck ring with those results. Pulling the head I discovered perfect "no ridge" cylinder walls but an exhaust valve with a pinhole in it. The inner pinhole was so small that oil plugged it to raise the compression during the check but would leak pressure during a dry check!

[ja17]

Hello Greg,
Yes this is more typical than bottom end problems. As the vavle gets worse it seats higher in the head making the valve adjustment tighter and tighter.

The later M180 engines had re-designed valve train with improved adjusters and the addition of valve rotators to prolong valve life.

Joe Alexander
Blacklick, Ohio

[Sokoloff]

Plugs have been in for about 8500 miles. Did the compresion test with a warm engine. From all the information I could gather on the car, I am about 98% certain that the mileage shown on the odometer is accurate. Just used a syringe full of Marvel oil in each cylinder, maybe a tablespoon.

My plan right now is to switch the lock nuts and adjusting screws for #3 and #1 and also switch #4 and #2. If I find that #3 and #4 are still loosing their clearance, then I'll look at the bushings maybe. If I find that the problem moves to #1 and #2, then I'll know that it is the screw and/or the lock nuts. Of course, I'll look for the worn adjusting screw indications you mention when I take them out.

Thanks for your input.

Len

[john m]

Hello sokoloff
RE: Did another compression test today, including wet on the two low cylinders. Here are the results:

1 90 149

2 89 142

3 85 135 wet 90 162

4 75 120 wet 90 146

5 85 138

6 90 150

Since the compression came up so much with the wet test, the problem probably isn't with the valve and the seat being burned but rather something with the adjusting nut/screw. The plan is to swap the adjusting screw with the valves that are holding the clearance and see what happens. Plans are also to get all new lock nuts.
Other input welcomed.
Len

The results indicate three possible conclusions.

#A. Bad valve seat to face seal (carbon) combined with bad valve stem seals #3, #4. and #5.

#B. Failing head gasket on #3, #4. and #5.

#C. Bad rings on #3, #4. and #5.

What you need now is a special tool called a compression leakdown tester; here are links to a few choices.

http://buy1.snapon.com/products/diagnostics/eepv309a.asp?partno=eepv309a&dir=catalog

http://shop.store.yahoo.com/pitposse/testers.html

http://search.ebay.com/search/search.dll?cgiurl=http%3A%2F%2Fcgi.ebay.com%2Fws%2 F&krd=1&from=R8&MfcISAPICommand=GetResult&ht=1&SortProperty=MetaEndSort&query=cylinder+LEAK+DOWN+TESTER

http://www.etoolcart.com/browseproducts/Index2.html

http://www.powersportsnetwork.com/enthusiasts/catalog_items.asp?catalog=776&levelcode=6154

http://www.thetoolwarehouse.net/shop/TTW304.html

http://www.thetoolwarehouse.net/shop/STR-CLT2PB.html

http://oemproamtools.com/auto/clt2pb.htm

http://www.racerpartswholesale.com/long29.htm

http://www.etoolcart.com/browseproducts/Cylinder-Leak-Down-Tester-CLT2PB.HTML

https://www.prostreetonline.com/pso/pages/products.asp?producttype=Engine&producttypesub=Accessories

How to use a compression leakdown tester:

http://www.morrowmarsh.ca/concours/techpages/leakdowntester.htm

http://www.xs11.com/tips/misc/misc3.shtml

http://www.revscene.net/Articles/Leakdown/

http://www.motorcycleproject.com/motorcycle/text/leakdown.html

http://www.mgdriversclub.com/tech/cylinder.leakdown.test.html

http://www.mbmopar.com/Hot_Topics/hot_topics.htm

http://www.geocities.com/dsmgrrrl/FAQs/leakdown.htm

http://www.vclassics.com/archive/leakdown.htm

http://www.w-p-c.com/buggyleakdown.htm

http://pw1.netcom.com/~wceng/articles/leakdown.html

http://www.type2.com/library/engineg/leaktst.htm

http://www.autosite.com/garage/repairqa/ques057.asp

Your spark plug picture shows me:
Oil fouling on #3 and #5
Heavy depositing on #6

Oh; to answer your other question:
"Budweiser", Anheuser-Busch.
And your car sounds like a six pack, LOL

Have a great day

[Bambo Jr.]

Joe,
Appreciate the info. Can the later model engine (180) valve rotators be used on my 127 engine without modification or is it a design adaptation impossibility?

[ja17]

Hello Greg,
No these upgrades canot be installed on the early M180 or M127 heads. The entire later cylinder head with the later improvements can be switched. There are a fair amount of parts that would also have to be changed on the M180 to use the later head, (longer timing chain, camshaft, rockers, valve cover and misc.) I would not be surprised if just the later series head is available from Mercedes.
In any case a good parts car or donor engine would make the job fairly simple and inexpensive. The latest version of the shop manual suppliments describes some of the changes and oimprovements in the M180 cylinder heads. Greg your M127 engine is a close relative of the M180 but different. Your cylinder head is halfway between Len's M180 and the latest M180, M127 cylinder head. You have the later style valve adjusters and rockers but no valve rotators. The next year production on your M127 engine did have the valve rotators. This head swap would be fairly easy.
Joe

[john m]

Hello Bambo Jr. (Greg)
Thank you for the nice picture of valve with hole.
Note: I only posted the top three possible; a compression leakdown tester will identify the actual cause.

The results indicate three possible conclusions.

#A. Bad valve seat to face seal (carbon) combined with bad valve stem seals #3, #4. and #5.

#B. Failing head gasket on #3, #4. and #5.

#C. Bad rings on #3, #4. and #5.

What you need now is a special tool called a compression leakdown tester

[Robby Ackerman]

I wouldn't be surprised if your valve is tuliping.

[Walt Puryear]

With older cams, the base circle can vary several thousandths, so when you check clearance it is important that the cam lobe be in exactly the same position each time. Also the engine temperature should be the same - cold.

Walt Puryear