Getting ready for some engine work on 7020

Have had my 7020 PS for 3 or 4 years. Has been good to me, used mainly in the hay field. Showing around 3900 hours. Has always been hard to start. Had the injection pump rebuilt last year, and planned on injectors this year. Had a pop through the exhaust when under a load. Originally thought it was because of the straight pipe on it, but started thinking otherwise last year. Decided it was time to look deeper in to it before the spring rush gets here.
Pulled injectors and checked compression yesterday.
#1-150 #2-200 #3-260 #4-0 #5-180 #6-260
These are cold psi, turned over with starter. Definitely have a #4 issue. Thinking a valve. Everything on top is good, no rocker or push rod issues. This tractor used very little oil last year, doesn't get hot, and actually ran very good for only firing on 5 cylinders. Does have a fuel haze, but mostly only at idle.
Planning to get head off this week and see where we are. Although the compression numbers seem low across the board, the lack of oil consumption and no major blow by makes me think rings are not a huge issue. Unless I can't find a problem with the head I'm leaning towards not doing a complete O/H. Tractor gets 100-200 hours a year, and may not even run all winter.
Will be looking for a good machine shop to send head to. I'm in Eastern Ohio, south of Youngstown, so would like to find someone within driving distance to save on freight. I would like to find someone who knows these old tractors. I've dealt with several shops over the years that I have not been confident in their ability to diagnose and repair the issues that comes with this older equipment.

First of all, to get an accurate compression test, you would need a fully charged battery with a battery charger running to maintain full charge.

Many times a push rod adjustment screw has backed off allowing a push rod to jump out of place. Pull the valve cover and check all tappets .017" COLD.

I, personally, don't have a lot of faith in leakdown tests. In this case, I don't see what good a leakdown test is going to do, especially when you are showing no compression on one cylinder. All a leak down test will tell you is if there is some kind of a leak in the cylinder (rings, valves head gasket or a crack in the head or sleeve).

every time i have not done a preasure test or air check  on somthing whether it be on a engine or a transmission hydralic syestem because i thought i knew better it has allways cost me more money and time and that dont bring home the pay check

How would this work? Before ripping it apart,pull 4 injector and valve cover to be sure 4 is on TDC compression. Rig a hose you can jam down injector hole with a blow gum attached and force air into cylinder to see if you can hear it leaking past valves or piston into crankcase. Listen to manifolds and breather.

That will do it! lmao!

If the head isn't cracked, it would get new copper sleeves for the injectors if it was mine.

Allis dealers (not all) had the tooling. Not most machine shops.

DanWi wrote: Just curious What would cause damage like that detonation or something going thru the engine? Timing off causing it to run hot. I suppose a person can get all the head stuff in order and put it back together with a good pump and injectors, but I would wonder what caused it.

I am very fortunate. I have a very good retired AC mechanic with all the AC specialty tools to help me. You're 7020 head is one of very few models with the copper/injector tube set up. Make sure you find the right shop to do your head. I do like my 7020, it's the 301 at it's best. IMHO. By the way, if you have time, while your tractor is down, pull the pan and check rod bearings. We replaced them on the 7020 and 8070 this winter. Really not that expensive.
Leon B Mo

This is another of those kind of rare problems. Gas exhaust valves were more frequently replaced because of burning. The diesels, not so much, but it does happen. That particular valve hasn't been doing its job for some time. Hard starting and low power go with that sort of damage. A trained ear can hear that wheezing, when the engine is turning over, quite easily. Your popping noise is the compression going right out the exhaust. When an intake valve does something similar, it pops back through the air cleaner.

I would guess that it started as a tight or warped valve which started leaking combustion gasses which quickly leads to cutting torch effect. Burned it away not a chunk broke out.

WOW!  Good job.  You'll be happy when it's fixed.  Should start good and run "like new".


Edited by GSTROM99 - 20 Feb 2024 at 7:55am

I received the injectors, and they are AC holders, so no chance of installing them backward. I'll hold off a while until you verify the head is usable.