Causes of low compression

[Eagleview]

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[Eagleview]

It is not the rings and is not the cranking speed if you can make the exhaust flapper move when you put shop air into the cylinders .

It is the Exhaust valves leaking . You need to take the head off and find out why they are leaking . Are there stellite seats fitted to the head ? If so , I am thinking THEY are what is leaking . The valves are not bent as they would have seen this when they ground them . You said you had lash so it is not that . You said the timing was correct so it is not that . The machinist would need to be tripping to install too long a valve guide which would bind on the valve head to stem taper so it SHOULD not be that . Lay the head upside down on the bench(valve stems clear of the bench) and put some regulated air into the exhaust ports , one at a time and spray some soapy water/WD40 etc onto the seats , I'll bet money they are leaking . The inserts will be loose or cracked .

 

[kevin37b]

Ether since day one ? Good luck .

 

[Tractorboy88]

Tractor is equipped with a 5" diesel starter.
I connected the 2 4DLT batteries in series to make it 24 volt system to increase cranking speed, but the increase did little to no effect on my compression. I compared readings to my 2000, which shows 350 psi compression (cold) and starts very quickly.

A fellow mechanic stopped by the shop today and suggested to replace the valve springs. If i have to pull the head back off to take to another machine shop, ill have all the valve hardware replaced, so if the valve springs have no effect, i'll already have the springs.

 

[IH3444]

Were the seats cut also? This is usually done after installing new valve guides. I'm also not a fan of grinding valves. You usually grind down through the hardened surface into the softer metal. This means that your valves will need checking more often, and will then sink into the hardened seats. Hardened seat rings are made of a harder steel so they can take cutting. Usually just a slight top trim to ensure the valve is hitting the seat perfectly. This does sound like a valve seat slight leakage problem. Were the valves lapped in after cutting? IH3444

 

[Tractorboy88]

Were the seats cut also? This is usually done after installing new valve guides. I'm also not a fan of grinding valves. You usually grind down through the hardened surface into the softer metal. This means that your valves will need checking more often, and will then sink into the hardened seats. Hardened seat rings are made of a harder steel so they can take cutting. Usually just a slight top trim to ensure the valve is hitting the seat perfectly. This does sound like a valve seat slight leakage problem. Were the valves lapped in after cutting? IH3444

Really couldn't tell you. I would think so, the owner of that shop has been in business for 30+ years, but is mostly automotive work, not diesel.

 

[Tractorboy88]

Installed new valve springs and reset lash.
Rechecked compression and all 3 cylinders are at 300psi, give or take 5psi variation.

 

[davesl708]

Installed new valve springs and reset lash.
Rechecked compression and all 3 cylinders are at 300psi, give or take 5psi variation.

Looks like there is still over 100psi loss.

 

[Tractorboy88]

I read on another forum that these tractors run from 300+ psi compression and my manual states the compression ratio is lower than 2000 diesels. I've still yet to do anything to bed the rings in, but i do know the valves still leak with 100 psi air pressure and those new springs.

I'm calling the diesel machine shop tomorrow.

I just want the darn thing to start without ether!

 

[Texasmark]

Well if the shop did something wrong he did the same thing to all cylinders.......Maybe he ground the seats to the wrong angle and the valves don't have enough surface area seated due to a mis match of the head and valve mating angles.

Surely he "lapped" the valves after grinding.

 

[LD1]

I just did a head on a 4-cylinder.

Had the head milled and seats ground. But got new valves and springs/locks. For the cost to machine a valve, and the price of new valves, it was foolish to try to save the old valves IMO.

I agree with others that you have a valve issue. All new valves and springs for my 4-cylinder were ~$80 for the 8 valves and springs.

The angle of the valves and seats also need to be matched, but not the same. Its an interference angle. The valve and head are ground 1/2 a degree to 1 degree different. Then need lapped.

Take that head back, have them re-work it, and you should be all set.

 

[Texasmark]

I got out the 1965-75 Ford Tractor Service Manual covering 2000 through 7000 and 3400 thru 5550 in response to my comment this morning about valve facings. Quoting from the manual:

REFACING VALVES

The valve refacing operation should be closely coordinated with the valve seat refacing operation so the finished angle of the valve is 1 degree MORE than the valve seat to provide an INTERFERENCE angle for better seating. Adjust the refacing tool to obtain a face angle of 45 degree 30 minutes as shown in Fig 20 (Part 1, Chapter 1 of the manual).

In looking at Figure 20 the above statement is not properly stated. The interface between the valve and seat is 1 degree interference fit. However, per the Figure 20, 30' of that is shown to be excess VALVE material/slighter cutting angle and the other 30' is the same for the SEAT.

So the valve is undercut (slighter angle than 45 degrees from a right angle from top of valve to face runout by 30') and the seat is undercut by 30' also providing the 1 degree interference fit.

Going to betcha your machine shop didn't know this and may be the root of the problem as the subject states..........."for better seating". The specs for 3000 gassers and diesel are the same so it's not a diesel unique issue, probably a Ford unique issue and going to bet you the shop may have missed it since you made the comment about their experience being what it was. Why not something like this? You covered seemingly all the other bases. It's an easy error to miss, affects all cylinders, allows/can allow exhaust gasses to escape to make your flapper flap while cranking, makes for lower compression.........

Good luck,
Mark

 

[Texasmark]

I just did a head on a 4-cylinder.

Had the head milled and seats ground. But got new valves and springs/locks. For the cost to machine a valve, and the price of new valves, it was foolish to try to save the old valves IMO.

I agree with others that you have a valve issue. All new valves and springs for my 4-cylinder were ~$80 for the 8 valves and springs.

The angle of the valves and seats also need to be matched, but not the same. Its an interference angle. The valve and head are ground 1/2 a degree to 1 degree different. Then need lapped.

Take that head back, have them re-work it, and you should be all set.

The Ford manual does specify a 1 degree interference fit, but both valve and seat are ground exactly the same sharing half of the 1 degree interference each. But I was surprised to read that as I too am used to the angles be different but also having the interference fit. The Ford manual states "for better seating" and with them identical there would be more metal to metal contact to help in effecting a good seal. I recall years ago that the different angles were to aid in preventing valves from sticking shut (engines that sat up for long periods.....like old tractors) course that's due to less material contacting so you trade off less material contact for not sticking. Course the more metal to metal contact the cooler the valves will run due to improved conduction cooling. Does seem like his solution considering all that's come before this and his findings.

 

[Tractorboy88]

Thanks for the input guys. I was able to get the head to the diesel shop I used for my 2000 on Thursday. He has a way of vacuum testing for leaks and said he would check first. I'll update when I hear from him or when I have other news, until then, we wait.

 

[LD1]

Sounds good. Keep us posted on what he finds out, and how he fixes it

 

[Tractorboy88]

Got the cylinder head back from the machine, again.

New valve seats, valves, springs, seals. retainers and locks. Vacuum tested and magna-fluxed.

Installed the head and set the lash.

Checked compression, 375 psi. on all 3 cylinders! Clipped on the air hose and held the engine on compression stroke, and the only faint hiss was by the rings.

I think we're in the ballpark!

Installed the injectors and lines. Started cranking to bleed out the system. No fuel! What in the world?

Pulled the pump, made a few quick checks and then took it to the pump shop. The plungers were stuck, $792 to rebuild with a new head.

Son of a biscuit.

 

[The Fred]

Post #32 BINGO we have a winner! Super Duty Dan gets a free case of beer!!!!!

Fred

 

[JRobyn]

Sucks! Glad you got the valves sorted though, wow, how could any decent machine shop have let that get by?

 

[The Fred]

I can tell you because I replace a fair amount of valve guides myself, the concentricity of the valve moves once the guide is replaced and it takes a bit of cutting to correct it. The real machine shops use a Serdi valve seat machine to get it right the first time.

I use Neway seat cutters and use a dye to make the initial check, then after final cutting and lapping a vacuum check tells the story.

Regards, Fred

Home

 

[Tractorboy88]

Sucks! Glad you got the valves sorted though, wow, how could any decent machine shop have let that get by?

I can tell you because I replace a fair amount of valve guides myself, the concentricity of the valve moves once the guide is replaced and it takes a bit of cutting to correct it. The real machine shops use a Serdi valve seat machine to get it right the first time.

I use Neway seat cutters and use a dye to make the initial check, then after final cutting and lapping a vacuum check tells the story.

Regards, Fred

Home

The first machine shop i sent it to performs 99% of their work on gasoline engines. He did mine as a favor since he knew me and business was slow. I asked him to put new guides, seats, and valves in, but he told me a set of guides and a simple grind would be all it would need.

Maybe he didn't realize a proper valve job was critical in a diesel because of the higher amount of compression.

Maybe he let one of his slacker employees do the job.

Maybe hes just getting old and senile.

Who knows, but i've heard several others tell me hes had a bunch of comebacks in the last 2 years.