4020 Diesel Hard starting

David G · May 24, 2009

I have a friend with a 4020 diesel that will not hit a lick when hot, but let it sit a while, prime and it will start right up. The engine also runs rough at high speeds.

Thanks in advance.

4010 puller · May 24, 2009

Sounds like injection pump issue. What year is it?

David G · May 24, 2009

buickanddeere · May 24, 2009

Fuel pressure between primary and injection pump?

Bob · May 25, 2009

TYPICAL of a Roosa DB pump with a worn "hydraulic head".

When it won't start, poor a bucket of cool water over the injection pump's hydraulic head (the area where the injection lines connect), wait a few minutes, then try to start it. If it starts then, you have "nailed" the problem as a bad hydraulic head.

DO NOT poor cool water on the pump while cranking or without waiting a few minutes.

bob15 · May 25, 2009

Bob, how does the "hydraulic head" wear out?

Also, pouring water on a hot head and rotor can cause an involuntary lock-up or a siezure.

bob

Tx Jim · May 25, 2009

bob15,
I'm not Bob
But the head gets too much clearance from 1000's of turns so that when pump gets hot fuel thins enough that pump can't build sufficient psi. Same principle as as a hyd pump losing psi capabilities.

Bob · May 25, 2009

"how does the "hydraulic head" wear out?"

The head and rotor are a precision-ground matched set and when they wear the clearance between them becomes great enough to let warm, thin, diesel slip through so the pump can't build enough pressure to "crack" the injectors. Therefore, no start.

The head will NOT seize if you do as I posted and pour water on it, wait a couple of minutes, then crank it.

I did NOT suggest pouring water on a hot pump when the engine was RUNNING, which CAN cause the pump to seize.

bob15 · May 25, 2009

The clearance between the H & R will not change, it can't, because they never touch. You WANT the thin layer of fuel between them, if not, you have a siezure. The clearance between the head and rotor can range from around 100-120 millionths to 200 millionths depending on the customer, but at no point does the head and rotor touch, except for the keepers, if the lapped surfaces touch while the pump is spinning, bad things will happen.

As for the fuel becoming hot and thin, yes that is correct. However to fix the problem, the pump should be rebuilt because it probably needs new, oversized TP blades. If it was put on a test stand, the return fuel will be too high. It ins't a worn out H&R, because they will be re-used, but rather worn out TP blades.

bob

Bob · May 25, 2009

It's good to know the "heads" never wear out!

bob15 · May 25, 2009

I work at the Stanadyne engineering center, in CT, I mainly work with experimental electronic pumps, models DS & DE.

I just never heard of the wording of the H&R as you had put it, no offense meant.

bob

J.ReinkeFarms · May 25, 2009

People always forget the rule of thumb that I was taught way back in the way back about diesels.

-If it starts hard cold you have a compression issue
-If it starts hard hot you have injection pump/fuel pressure issues.

4020 Diesel Hard starting

David G

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