LEAK DOWN RATE TEST RESULTS

[PGWIN]

Following on to a long path of getting my 12V to run great again I did a leak down RATE TEST on my 12 valve because it hasn't been running up to par and this was the next step after going through the fuel system.

Results are below - this is the average of 3 meaurements (really more 3 repeatable measurements of the same value on each cylinder), at 100PSI, with piston at TDC for each cylinder, using a MAC leakdown tester:

#1: 4%
#4: 24% - audibly louder than the others, sounds like it is coming out the intake valve listening through the intake manifold.
#2: 10%
#6: 11%
#3: 7%
#5: 16%

The fact that they go from 4% to 24% and audibly much louder on #4 leads me to believe this could be my problem, or at least the leakage rate would be concerning of a valve problem on the verge of getting worse quickly.

I'm inclined to pull the head to at least have a known good baseline understanding on the mechanical condition.

Any words of wisdom or thoughts on this would be greatly appreaciated.

(this is the fuel system path I had followed before this) thought this deserved a separate thread as it is valve/head specific issue: https://www.turbodieselregister.com/threads/something-not-good-has-happened-
to-my-cummins.259570/#post-2523835

 

[PGWIN]

Any interest in this subject?

I did pull the head , cylinder croosshatch looks really good no evidence of scoring so I am hoping my issue are in fact leaky valves.

I did not see any evidence of a valve smacking a piston.

Waiting for torq valve spring compressor and then will remove valves.

Can any one offer tips on what to look for after removing valves and / or what exactly you would recommend in the rebuild - I'm only planning mild power increases for towing heavy.

Thx

 

[GAmes]

I went back and read the thread. (btw, the link doesn't work, probably because it didn't print all in red) How many miles are on the engine? More than likely all you need is a standard valve job, maybe resurface the head. I'm convinced that Felpro makes the gaskets that are in Cummins packages. As you probably know, the Felpro will cost less. On the other hand, a Cummins top gasket kit will provide every little gasket you need for reassembly plus a handy measuring gauge for the head bolts. They are reusable.

 

[GAmes]

Also, you might consider an after market exhaust manifold since you are there.

 

[crabman]

Just to confirm what you suspect. You can do a water/air leak check with the head off and it will show you which valves are leaking. There are several videos on YouTube showing how to do this.

 

[PGWIN]

Thanks for the tips. Will look up the water test. Yes the Cummins gasket kits are like 329$. I'll need to do the trade cost for the two options.

110k miles on the truck - which is why I am a bit surprised of the valve leakage, but maybe excessive heat can cause this - the prior owner didn't have a pro and towed heavy but allegedly never in 5th. Initially I thought maybe I floated the valves with the exhaust brake one time that may have compromised sealing - but that doesn't "appear" to be the case.

One question a noise I hear when rotating the engine: with the head on and rockers intact - I could rotate the engine by the harmonics balancer bolts and it was silent except for escaping gas. I then removed the head and turned the engine to move cylinders to wipe any coolant off the cylinder walls that spilled down - but noticed an internal clunk/noise wihile laying on the ground turning it maybey about every 1/4 turn I could hesr it. Would this be the tappets falling on the cam - since they are not being compressed but the rocker assembly?

And ... the link from above hopefully works now: www.turbodieselregister.com/threads/something-not-good-has-happened-to-my-cummins.259570/#post-2521667

 

[PGWIN]

It is also interesting that the two highest leak rates cylinders correlate to the intake valves with the greatest lash. I coppied the measurement results from the link above. It would seem the valve lash is greater because something is preventing full seating (bent valve or burned valve?) The exhaust valves do have i think 60 lb springs - well significantly higher than the intake valves. My original target lash was .009/.018 and I never saw lashnincreas such as in #4/5 intake below.

Cylinder / Int / Exh

#1 / .008 / .018
#2 / .008 / .017
#3 / .009 / .018
#4 / .0115 / .019
#5 / .011 / .018
#6 / .008 / .0185

 

[GAmes]

Not that I think .001 is a big deal but the spec is .010/.020 Now that the head is off overthinking the past and speculating is a waste of time. You don't know the total history and never will. Since it only has 110k there is a possibility it is a manufacturer flaw.

 

[PGWIN]

Thx - I found a good shop to grind valves at least recommended by 2 independent people - Del' s machine in Sacramento. They clean, magnaflux, grind reassemble, and do Cummins 12V heads daily.

I think I'm inclined to go with the 3 angle grind. Is there any downside to this.? I wonder why it would not be a factory design if it is better (more machining is cost?).

Wrt the Gasket sets after some research I feel comfortable with the Mahle set of which I use their OE components on BMW and have always been pleased with quality - they are priced like Felpro about $100 for upper set vs $350 for Cummins. I think they possibly could be an OE for Cummins.

Then decided to deal with the I deal with the killer dowel pin since all apart. Pin is about a good 1/8" on its way to major damage so will tab that and re-torque bolts per recomendations.

 

[PGWIN]

Update:

HEAD machining done: valves seats machined new valve guides, and .007" milled off the deck (warped).

Decided to pull injection pump to have it bench tested For balance BUT 250 ft-lbs with a torque wrench didn't phase it and then a breaker bar with pipe extension (3 ft lever arm) and at least 300ft-lb didn't budge it.

Any suggestions to get this nut off - is this common that it would take this load and not budge?

 

[GAmes]

That is definitely excessive. A PO might have over torqued it. It should only be 144 ft/lbs.

 

[PGWIN]

Ok different pipe with a levermof 38" and about why I could lift on the end of it popped it. I'd say about a 110 _ 120 lb load is my max lift and I was about there = 330 - 360 ft-lbs ( now for the history only record I have of the fuel system being worked on was at the dodge dealer in about 1998). Timing is stock.

On to pull the gear now.

 

[PGWIN]

Called the local Bosch authorized pump shop. Seems a very decent shop. I wanted them to check balance, check ask seating, increase fuel adjusting

Issue is they will only set to spec due to (of course) gov regulations. I was hoping to install 3k ask before and have them increase fuel output but all is limited by factor spec.

Also not sure how a modified fuel plate/star wheel effects what they will do?

So installing 4k gsk afterward defeats the pump setup at shop.

Any thoughts on how to handle this? Which no could do all myself!

 

[GAmes]

Where are you? The authorized Bosch shop in Austin, TX is also a speed shop. The owner, who drives a '96, had designed a towing plate that he installed in my pump while it was in there to fix an oil leak. He would have installed a GSK too if I had wanted one.

 

[PGWIN]

In Sacramento , Ca.

 

[GAmes]

CA, say no more. You might check Reno to see if they have a Bosch shop.

 

[PGWIN]

Yes I'm aware of the Ca issue - 2x4's, air, trees and yes the 32oz soda...... are all list as official health hazards and thus require gov control!

Anyone have experience with Reno shops?

 

[GAmes]

Doing a quick google all I could find was Sierra, and apparently they send the pumps and injectors out. You might have to send it to http://theaustinfuelinjection.com/ or another Bosch shop that is out of state.

 

[DonFitzwater]

I'm very surprised your head wasn't cracked. I've done about 7 head swaps in the last half dozen years on 12 valve engines and they were all cracked from injector bore into valve seat area of the head. Some were abused and some not. None had leaks or other problems from the cracks, all needed head gaskets from normal wear and tear.

I've had fantastic luck with Oregon Fuel Injection as well as Industrial Injection. Both are quality companies in my experience (5 injector pumps, VP44 and P7100)

 

[PGWIN]

Well, actually there were two very small cracks ( magna flux). Shop that did the work is very reputable - does 12V heads weekly. I talked it over with him - his perspective was it was better than the last 50 heads he had seen, he said if it was him he would use it.

PUMP REPORT: Update just got the injection pump back, I went locally Zac a baseline at the Bosch shop. Pump is about 12% higher out put than stock. No issues. #1 barrel was slightly out of spec (high) and adjusted back. Pump made in Brazil- which in his opinion was better than the made in India pumps. So at least there is one unknown out of the way.

#ad

TAPPET COVER GASKET DECISION: I was contemplating replacing the tappet cover gasket. It doesn't leak now, is original. Original thought was leave it alone if not leaking. I've seen reports on failed replacements. One reference to the Mahle gasket being a better design than Cummins (allegedly Cummins made decision to compromise two designs into 1 - which is "less forgiving). I have the gasket in Malhe kit.

Jury is out, at 110k miles (Yes 25yrs old) risk it and replace, or leave alone? Here's where lack of seeing hundreds of trucks (experience) shows up!. Votes?