leak down test results - Page 3 - PeachParts Mercedes-Benz Forum

llm4 · #31 04-01-2011, 06:28 PM

The link is the type of tester I used.
http://www.saferacer.com/longacre-leak-down-tester.html?productid=1958&gclid=CLeIv--T_KcCFQbe4AodiRHyqw

-I connected the tester to the injector holes for the first test (when rebuilt injectors). For other tests I used the glow plug holes.

-I installed the springs myself, not the machine shop. I didn't check them in a spring rater but they all were the same height and took a lot of pressure to get the nut started on the valve. I hope this is acceptable

-I need to rephrase build-up. I think the leakage problem is making the build-up happen. I hope that is clearer.

- Leak test was done at TDC of each cylinder and did not have to lock the crank. I made a homemade "timing tape" to determined TDC for each cylinder and marked the balancer. I can post the procedure I used to mark the balancer if needed.

Thanks again!

leathermang · #32 04-01-2011, 11:06 PM

Unless your problem is fixed... yes, you need to post a description of everything you did and how you did it...
This stumble... the same at all 'RPM's ?

llm4 · #33 04-02-2011, 08:57 AM

Its throughout the entire RPM range. Its not a dead cylinder but a weak one. Its not as bad as cracking an injector line.

Here is the procedure I used to mark the balancer:
*A 4 stroke engine has 2 revolutions per cycle.
*I wrapped a piece of masking tape around the circumference of the balancer and cut the ends so they touched. Carefully removed the tape and stuck it to a table top. Doubled the measurement (represent two revolutions), then divided the total length by 5 (# of cylinders). I took that measurement and cut a new piece of tape that long. I stuck the tape back on the balancer starting at the factory TDC mark, and then marked the balancer at the other end of the tape. Repeated that step 4 more times and end up back at TDC.
Follow the firing order and every other mark will be TDC for that cylinder. You can verfiy by looking at cam lobes for each cylinder.

That was harder to write than do.

I am going to pull the manifolds this morning and test again. I will post later if I find anything.

Thanks

leathermang · #34 04-02-2011, 11:19 AM

But how did you determine that the top of the piston was at ' TDC ' at the same time your crank pulley indicated that ?
You said you verified by the valves being closed.. but that is not particularly accurate...
Did you stick an extended dial indicator on the top of the ( or even A ) piston .. mark spots evenly on both coming up and going down.. then split that difference to determine Actual TDC ? In other words... you are assuming the pulley is not rotated on the crank ?

Stretch · #35 04-02-2011, 03:05 PM

If I were you I'd take off the valve cover and check to make sure that the valves are closed when you perform your leak down tests.

I would also try doing a leak down test with a lower pressure as you may (just may) be turning the crank at 100PSI. But I have a sneaky feeling you are making a measurement when a valve is open.

EDIT:- Oh yes forgot to say. On the valve cover you've got the firing order nicely cast into the top. Follow this order - checking that the valves are closed for each cylinder.

vstech · #36 04-02-2011, 03:13 PM

Quote:

Originally Posted by leathermang

But how did you determine that the top of the piston was at ' TDC ' at the same time your crank pulley indicated that ?
You said you verified by the valves being closed.. but that is not particularly accurate...
Did you stick an extended dial indicator on the top of the ( or even A ) piston .. mark spots evenly on both coming up and going down.. then split that difference to determine Actual TDC ? In other words... you are assuming the pulley is not rotated on the crank ?

this would be difficult to accomplish with a IDI diesel... you'd have to pull the prechambers.

Chas H · #37 04-02-2011, 03:48 PM

A valve can be used a TDC indictor. Let the piston push it up untill it goes no further.
But the TDC mark on the front pulley should be accurate.

babymog · #38 04-02-2011, 07:01 PM

The timing indicator on the front cover is adjustable, needs to be set properly.

I did mine with the head off, with the head on you'll need to pull a prechamber as John mentioned. Be careful doing this though as the prechamber fits into a depression in the piston, need to be sure that your dial-indicator rod doesn't get hung up at an angle.

leathermang · #39 04-02-2011, 07:45 PM

WHEN PULLING THE PRECOMBUSTION CHAMBER.....

THE GLOW PLUGS MUST BE TAKEN OUT FIRST !!!!!!!!

layback40 · #40 04-02-2011, 08:03 PM

Leak down test should not be done at TDC. About 1/3 of the way down the stroke is ideal.
Has the OP tried doing a test after placing some oil in the cylinder to see if it seals it up?

leathermang · #41 04-02-2011, 08:06 PM

Quote:

Originally Posted by layback40

Leak down test should not be done at TDC. About 1/3 of the way down the stroke is ideal.
Has the OP tried doing a test after placing some oil in the cylinder to see if it seals it up?

Agreed... AND it means some method of LOCKING the crank is needed for safety...and for it to stay there long enough to do readings... He did not mention adding oil that I saw... which should have been the part which showed how much of the leaking was being caused by the rings...

layback40 · #42 04-02-2011, 08:21 PM

Another clue. After I removed the head, when removing the intake valve from the #4 cylinder I noticed there was a tremendous amount of carbon (or crusty oil) build up on the backside of the valve and intake port. It was so bad it was almost blocked! This was not normal and I was convinced the valve may not have been seating properly due to build up and leaking by. Maybe this is an indication of the problem.

I would have thought this was caused by a bad valve stem seal. It shouldnt cause the valve to leak though.

As a kid, (back when Noah was building the ark) we used to place the head of gassers on their side & fill the inlet/exhaust ports with petrol, if the valves needed doing you would see the petrol leaking into the combustion chamber around the valve seats. I think the same would work with a diesel.
The motor in question here sounds like it has a valve or 2 not seating properly. The head is going to have to come off again any way.

llm4 · #43 04-02-2011, 10:17 PM

I think I found it. Looks like I got a bad valve job. Need to pull the head again and see whats wrong.

Check out the video. I did a leak down test again, sprayed some WD-40 in the port and this is only with 15 psi.

http://www.youtube.com/watch?v=nx6-c6BTXzk

Thanks again for everyone's help! I will post an update after I pull it apart.

leathermang · #44 04-02-2011, 10:23 PM

What a bummer !!!

barry123400 · #45 04-03-2011, 11:45 AM

Well you learn or refine something everyday. I will put the heads on their sides and add thin fluid to the chambers on any head from now on as a pre head installation test. It just means you have to test twice.

Once for intake and once for exhaust valves before installation. Your issue might have been caused by really sloppy valve guides. This has the potential of causing your problem so check them.

When they are worn as you know the refference for getting the seats concentric is no longer there. My method I have always used of checking with the head on it's back does not sound as good. For another thing if there is a crack in the passage before the valve it might catch it.

I assume you put the intake valves in by a random choice method. Yet the problem remained on the same two cylinders. It is common practice to just change a few valve guides if the remainder are good.

Thanks to the member for the posting of an alternative head check method on this thread. I will always check the head unless I have complete faith the shop that ground the seats and valves checks their job well. Even then for the time taken it is easier than having to remove the head again.