MEP002A old style injector pump plunger problem

[donaldl]

Gentlemen;Earlier this summer I had problems with one of two of my MEP002a engines having its injector pump Viton spacer deteriorating.My earlier posts explained how to make one instead of paying AMBAC $38.I did manage to fabricate a spacer to get the engine running but I had to reduce the loading on my injector springs because my new spacer was leaking.I ask readers to send me the specifications on a viable Viton spacer so I could duplicate them exactly.I received no responses.So I reluctantly decided to get those specifications off the spacer on my other,running MEP002a.I removed the large cap nut ,then the delivery valve holder.Then I gently removed the delivery valve assembly.When the assembly came out so did the Viton spacer...in three pieces. Just what I suspected MIGHT happen.Well no problem I said....I made a homemade spacer before.I can make one again.But after numerous spacer attempts I could not get the unit to start.I was getting fuel to the injectors but the pressures were too low and the injectors could not spray.So I reluctantly sent AMBAC $38 for a new spacer.After installing the new spacer the engine still refused to run.Same symptoms,ie,low fuel volume and low pressure.So I removed the fuel pump.It was the old style pump and slightly different than the newer stlye,without the "Jesus clips"or the bowtie washer.Maybe simpler but without an exploded view still a challenge.I could not find any problems.So after cleaning it thoroughly I reinstalled it.I cranked the engine...It started!! Whoopie.I must have the Magic touch !(I would not have been working all month on it if I had that Magic touch).I guess that even though the fuel pump plunger was moving(I confirmed it before disassembly) it must have been stuck in mid travel and was keeping fuel pressures too low.Again I reinforced that old lesson....if it ain't broke don't try and fix it.But I still have homemade Viton spacers in both engines as I have confirmed they hold 300 -600 PSI factory pressures by testing them with my POP diesel pressure tester.So my earlier post on spacer dimensions I think are functional.BTW that old style pump had 2272 hours on it.Thats only 94 days of run time.

 

[dangier]

Donald,
May be luck or whatever, but I have never replaced the viton spacer (that little brown fabric ring?), in the delivery valves on the ip's I have got running (5). It's either been folded up inside or broken. First thing I have thrown away. All of the 002's and 003's are still running.
David
ps: let me know if we are talking about two different things....

 

[donaldl]

Dangier;;You are indeed talking about the same part.And I have read others on here running machines without that part.Yet both of my MEPs using old style IP as well as the later newer style IPs have them and WILL not run without them.
Onan makes a test adapter that screws onto a hydraulic pump and the delivery valve assembly,with Viton spacer,are put under pressure and must hold 300 to 600PSI to be considered mechanically sound.Without that spacer I could not maintain that pressure.
Why some machines need those seals and others do not must come down to tolerances.Hard to believe a military specified power system would be at the mercy of a .50 cent spacer.

 

[dangier]

Donald,
When I put together the delivery valve and screw in the holder in the ip, I have always had to tighten it up and give it the extra "tweak" to make it work. They are really tight! That may be the difference. First one I took apart was so tight that I thought it was stripped at first.
David

Another thought-Are you making sure that the original parts stay together in the delivery valve? I read somewhere that they are matched at the factory and lapped in for close tolerances. I have always worked on one ip at a time so parts don't get accidentally switched.

 

[donaldl]

Dangier;That is a clue;I have never really torqued to specs,just snugged that delivery valve holder.Since the delivery valve holder traps the valve assembly against the inside of the injection pump head then compressing it with higher torque readings makes sense.

No I have not mixed my components.But,according to shop procedure you can restore a mated delivery valve to it seat by using lapping compound.I assume that theory holds if you "had" to use replacement components.The delivery valve pressure test addresses relapping original parts if pressures are below 300-600PSI.I found a delivery valve test holder on Ebay and was able to do the test.Since both my MEPs are now running I will leave them alone.But I will keep your "theory" in mind next time I have any problems with the delivery valve assembly and run some tests using higher torque settings,then post those results.Thanks for the info,Don L.