Hydraulic Head Question

[GunInstructordotcom]

I finally got to replacing my HH on my 1970 M35A2C. All was going well until I noticed that the metal piece with the slot in it which is inside the rectangular port on the HH and engages the nub on the fuel shut off shaft, it moves up and down with resistance. On my old HH, it slips up and down easily. So I oiled it with some ATF and moved it up and down, which helped some. I installed the HH and when I inserted the fuel shut off shaft, the lever swings back and forth, but it is stiff and I have to help it return completely with or without the spring-assisted part attached to the lever. The U-shaped clamp on the shaft is less than finger tight, so that is not the issue. My new HH is a "Diesel Fuel Injection Parts" brand in a blue box with white writing. It was thoroughly wrapped in several layers of plastic and inside a plastic box with red caps on the injector line holes. When I bought it some 3+ years ago, it was advertised as NOS. There is no ID plate on it. The part number is HD90101A, name is "Head Rotor". So my question is, can I repair the stiff part such as taking apart the HH and polishing the shaft that the slotted part rides on? Or is this out of my league and I should just b uy another HH?

 

[Elk1111]

You can take it apart and clean it but don’t use anything abrasive. The tolerances inside the hydraulic head are very tight and it will leak if those aren’t kept.

 

[GunInstructordotcom]

You can take it apart and clean it but don’t use anything abrasive. The tolerances inside the hydraulic head are very tight and it will leak if those aren’t kept.

Being that the HH is new I'm wondering if it is a defective part. I'm guessing that the C&C HHs are Chinese manufacture, so that's a possibility.

 

[rustystud]

More than likely it has dried assembly lube on it. Taking it apart and cleaning with brake clean and reassembling it with some oil will do the trick. Or you will find something horrible in there !

 

[Floridianson]

Guess it all depends if you want to go to all the trouble of pulling the head completely off and tearing it apart or something maybe more simple. My two cents if it was just assembly lube then the diesel fuel running through the head would clean that off. Can you still move the fuel control unit assembly with your finger from wide open to shut off when everything is assembled? I will say I had some hydraulic heads rebuilt from Ambac and sold them on steel soldiers and they may have had a light coating of machine oil but that's about it to prevent rusting. Myself I might try this first. If the fuel control unit assembly is moving free enough with your finger with just a little resistance you might try this. Leaving the timing shut down cover off have soldier b hit the start button. The fuel control unit assembly should be at the 7:00 position to start. As soon as it starts use your finger and move the fuel control unit assembly towards the rear but not all the way or it will shut off. You're just trying to lower the RPM to idle. Then let it run for a while and see if the fuel control unit assembly freeze itself up. When you need to shut it down just with your finger push it all the way back towards the firewall to the no fuel position. Also don't forget to add some power service fuel cleaner and don't be afraid to double the portions.

 

[GunInstructordotcom]

I pulled the HH and compared it my old one. The shaft of the old one is polished, the new shaft has scratches running along it. It is thoroughly lubed and yet the new slotted piece drags along the shaft. I believe it has burrs in the hole that the shaft rides in. I have to force the piece to move up and down with a small screwdriver. Taking it apart and examining the surfaces for burrs or machining marks is next. Also, to eliminate the possibility there is hardened lube in it.

 

[Floridianson]

Send it back to distributor. That's a shame it had to happen to you but as per the TM you're supposed to check that before you installed the head. When holding the head up right the sleeve should be at the bottom. flip it upside down and the sleeve should slide by itself down the plunger by gravity. All the Ambac heads that I had were rebuilt and pass this test.

 

[GunInstructordotcom]

Yes, you're right, I should have examined the HH three years ago when I purchased it.

 

[msgjd]

I learned in the 70's as a teen laying underneath a car stranded in a store parking lot during a snowstorm that we should also always test a rebuilt starter's function before installing it ..

Luckily a NAPA was only a half-mile walk and i had my tool box in the trunk , but still ! ... I made two round trips for two starters before I got one that spun

 

[GunInstructordotcom]

I learned in the 70's as a teen laying underneath a car stranded in a store parking lot during a snowstorm that we should also always test a rebuilt starter's function before installing it ..

Luckily a NAPA was only a half-mile walk and i had my tool box in the trunk , but still ! ... I made two round trips for two starters before I got one that spun

That must have been frustrating. At least I caught my HH defect before I completely installed it. Just a few low pressure lines and the four mounting nuts.

 

[rustystud]

That must have been frustrating. At least I caught my HH defect before I completely installed it. Just a few low pressure lines and the four mounting nuts.

I'm glad you decided to take it apart. You never know what is in there unless you look.

 

[rustystud]

Yes, you're right, I should have examined the HH three years ago when I purchased it.

Who takes apart a brand new part to inspect it ? You did nothing wrong. Anyone of us would have done the same thing.

 

[Floridianson]

Nothing to take apart when you are checking to see if the sleeve slides freely on the plunger. Just flip it upside down. That way you can make a decision as to the problem and possibly fix it. Yeah I would think after 3 years the distributors probably not going to be any help. As soon as I get the chance I'll go through the TM and post it on the sticky about replacing the hydraulic head. Really no big deal but it is a pain in the butt have to install a head and then have to remove it for something that might be a problem that can be repaired before we install the head. I replaced quite a few heads on non running trucks back before I had the overhanging tire and even then it wasn't much fun. Now I've have the spare tire I know it wouldn't be any fun.

 

[GunInstructordotcom]

I'm glad you decided to take it apart. You never know what is in there unless you look.

I knew something was wrong when I saw the scored lines on the shaft. They were not deep but they were scratches that are not supposed to be there, especially on a new HH. The hole in the ledge that slides up and down must be rough to do that and cause the resistance to sliding.

 

[rustystud]

You might be able to salvage this Hyd Head. After dealing with whatever is scratching the shaft you can take some "jewelers rouge" and polish the shaft back to a usable one again. You might need to use a really small ultra fine file at first to knock down the high ridges on the shaft.
Once the shaft slides smoothly in the bore you can check and see if it will still work doing a "vacuum" check on it.
To do this you need to clean the shaft and bore with "brake klean" or something that will clean and leave no residue. Once the shaft and bore are clean and dry, you will place you finger on the top of the bore and pull the shaft down with your other hand. Just pull it down about 1/2" and let it go. The vacuum you created should pull it back up. Then again placing your finger on the top bore hole, pull the shaft completely out. It should make a nice crisp "popping" sound. If it passes these two tests it should be fine to pump diesel fuel.

 

[Floridianson]

Be interesting to see if those scratches are the whole length of the plunger and would extend into the pressure chamber. Please let us know or have some pictures. I guess everybody's got to be the first at something so congratulations on being the first and having this problem supposedly a new part. Myself if the scratches are only in the lower chamber where the sleeve rides maybe you can get them polished out. I'm still wondering if CC would make good on this even after all the time passed.

 

[Elk1111]

What is everyone’s thoughts on using the plunger from the old head to replace on the new one?

 

[NY Tom]

What is everyone’s thoughts on using the plunger from the old head to replace on the new one?

New production HH from China do not include the plunger as far as I know.
You are supposed to use your old one.
While this does not seem to be ideal, I guess it works since they are selling the heads.

This is not correct - button and retainer are not included. My error here please disregard.

 

[rustystud]

New production HH from China do not include the plunger as far as I know.
You are supposed to use your old one.
While this does not seem to be ideal, I guess it works since they are selling the heads.

No plunger ? They need to fit the plunger to the Hydraulic Head. So they must sell the plunger with the head.

 

[rustystud]

What is everyone’s thoughts on using the plunger from the old head to replace on the new one?

It would be like finding a very small needle in the proverbial Haystack. The plunger was factory honed to the bore of the Hydraulic Head. I suppose if you found a plunger that was slightly wider than your old one you could hone out the bore, but you would need some extremely precise machining work to do this.
Than again you could get lucky ! Never hurts to try.