Compression test Mercedes OM 636

catmandoo

catmandoo

Well-Known Member
Joined
21 Aug 2003
Messages
1,803
Location
The Earth but normally in the place of the high st
Visit site
Anybody done a compression test on an OM 636?
Reason is That while best to use glow plug holes can't find a suitable adaptor to screw into them
One suggestion is to use an old glow plug and machine the electrics out etc however I would like to get the real thing .
Got a diesel test kit but the Mercedes requires a M18 by 1.5 thread etc and modern ones are pencil type M10s
One American site uses a M18 by 1.5 injector adaptor with an M10 pencil complete with Schroeder valve screwed into it . While I can do that I am worried about the seal in the M18 as it is flat bottomed and the thread is not tapered . Glow plugs and m10 adapters have a chamfer instead which mates with a cone in the engine block hole thus creating a seal

Any body done it before ?

I have a theory that with the schroder valve keeping the gauge pressure steady small leaks would be insignificant . However as we all know when on the boat with out that vital part all we can do is curse and swear and go home to get it
Wasted journey etc
 
Hi,

Actually just did it last night. I bought an M18 split die and opened the die as much as possible and ran it the whole length of the turned bar (3/4" hex bar turned to 18mm on one end), then part tightened it and went half way, then closed the die as much as possible and taped the first quarter. In my kit I used an adapter that had an m11x 1.25 thread but only had a m11x1.5 tap but the adapter seemed to screw in OK.

It tightened quite nicely in the glow plug holes and I figured it would only make the compression reading lower. Therefore if i had low compression I would need to investigate it and the adapter would be part of the investigation. As it was I had between 19 and 20 bar on all the cylinders with 4500 hrs since a rebuild in 96, so quite happy really. I did the check as my injection pump just leaks a little diesel out of the overflow and was thinking about having it rebuilt but will probably put up with the leak since the compression seems good and will wait until major surgery required.

If you can wait a week or two whilst I have a chat with the engineer I could probably send it up to you.

Or for a few boat maintenance tokens could make you one to fit one of the adapters in your kit.

Why are you testing: I had slow starting but cleaned the brushes and armature in the starter and that made starting faster, also finally put a new battery on a couple of weeks ago and now almost leaps in to life!

I did my injectors last year and now runs smoothly and is more responsive to the throttle (accepting it is an old diesel)

regards

Stav
 
catmandoo said:
I have a theory that with the schroder valve keeping the gauge pressure steady small leaks would be insignificant . However as we all know when on the boat with out that vital part all we can do is curse and swear and go home to get it
Wasted journey etc
Click to expand...

The cylinder pressure is an instantaneous reading and the Schrader valve would be irrelevant. Strikes me that a machined out glow plug would be your best answer.
 
birdseye said:
The cylinder pressure is an instantaneous reading and the Schrader valve would be irrelevant. Strikes me that a machined out glow plug would be your best answer.
Click to expand...
Not sure you are right . In the first place my test kit uses pencil M10 adapters which have built in schrader valves and secondly if you want to catch an instantaneous reading you lock the pressure in with the valve . Analogue dial and hose have pressure let down button to manually drop pressure in hose
 
Long story but new reconditioned engine has problem with fuel

1 contaminated with petrol 2009 Greek Island tanker
2 suspect injectors sticky due to biofuel and impact of FAME

Confidence builder after full service
Replace injectors
Clean old and keep as spares
Check torque head bolts
Check, reset tappets
Contaminated fuel caused runaway , loud bang and black smoke on arriving Datca Pier 2009
So had on my mind for some time now ��
 
Thanks for offer . Have ordered new bits including one glow plug so will check M18 adaptor against plug for shape may get away with copper washer .

Like cross section of OM 636 particularly last photo . Looks like Bosch injectors not TDz type also glow plug old series type not new parallel ones which are qui her start due to higher voltage
 
You must log in or register to reply here.

Share this page

Top