The Tractor Doctor
By Ron O'Neill
Cylinder heads need service from time to time. When the tractor just doesn’t run properly anymore, and all else has failed, we begin to look at replacing or rebuilding the cylinder head to solve the problem. Additionally, many times a coolant leak into the inside of the engine leads us to thinking that it could possibly be the head or the head gasket. John Deere tractor owners’ cylinder heads and their problems seem to find their way in front of me as often as carburetors do. It’s usually the same scenario…a greasy old casting wrapped in ‘swaddling’ clothes, lying in the trunk of a car or the bed of a pick up truck with the instructions “could you take a look at this?” After a short question and answer session regarding what the owner believes is wrong, and what trouble they have been having, a decision is made as to what needs to be done with the cylinder head.
Recently there have been 3 separate episodes of old John Deere cylinder heads that have crossed my path, and it is these that I wish to discuss …this being the first topic of conversation in this month’s article. We have a 630 with a previously rebuilt head; a John Deere 1939 H; and a John Deere 420. All had cylinder head troubles; all had different solutions. So here goes, and I hope that readers will find this information helpful regarding cylinder heads.
First the man with the 630; his problem---poor “runability”. The tractor didn’t seem to run properly and tended to change how it ran as it warmed up. We all know how ‘sweet’ a 630 can run, and that is what this customer was asking for. He had taken a compression test and found uneven and erratic
compression. The man said that he thought the cylinder head was the original one for the tractor and he felt that it needed to be rebuilt. Looking at the cylinder head even before “laying a finger on it”, I stated that I could see 3 things wrong right off the bat. No. 1; it was not an original head, but more probably a rebuilt one by the way the underside of the valve cover was painted. Original John Deere heads are not primer painted in this area, but they usually are when they are rebuilt to prevent rusting…this one was painted. No. 2; by looking at the head gasket and the flat surface of the head, the gasket was not holding. Recognizing this problem is best done by an arm’s length visual inspection. The head gasket and head surface should be a clear and shiny color all the way around the fire ring area. If you see a dark area on the gasket or head, it will almost always be from the combustion chamber to a water jacket, or from one combustion chamber to the other. Any dark area such as this means the gasket is leaking. Usually the gasket is the victim part, and you have to find why it leaked in order to fix the problem. This 630 head gasket was leaking both to a water port and between cylinders. My question here; “was the head gasket installed in the proper direction?” The customer stated that he didn’t know. Some head gaskets are marked “out” or “to cylinder head”; some are not marked. They must be installed with the smooth side of the gasket to the engine block, and the crimped area around the cylinders (called the fire ring) to the cylinder head. Any other way is wrong, and the gasket will not seal properly. I had my doubts whether this gasket had been installed properly, but I could not say for sure at this time. And, finally, No. 3; an immediate visual problem (without disassembling the head)…a pet peeve of mine…upside down valve springs. Most valve springs have at one end a number of coils that are wound closer than the other end. In other words, the coils at one end of the spring may be 3/8 inches apart, and at the other end only 1/8 inch apart. If you have valve springs that have tighter wound coils at one end, the spring must be installed with the tighter wound coils against the cylinder head. The spring was made to compress against the tighter coils, and its force (in order to pull the valve shut properly) relies on which way the spring is installed. I have seen countless numbers of rebuilt cylinder heads with upside down valve springs. The 630 head had 2 of the 4 installed improperly. That being said, the valves were removed; we then took a look at the valves and seats. Rebuilt cylinder heads almost always come with new replacement seats and new valve guides…that’s a good thing. New replacements seats look like the example in picture 1. They are installed in the head with about .003 or .004 press fit. After the seats are installed, and when the head is sold, it usually does not come with a set of valves and springs. This is because the valves must be fitted to the new seats by grinding the correct angle into the seat, and setting the correct seat width, and then landing it in the correct place on the valve face. Usually after this is all done properly, I like to finish it all off by hand lapping the newly refaced valve to the seat. In this 630’s case the valves were just installed onto the new seats; they were not fitted to mate each other in any way. The valve seats were very narrow as they came from the box, and the valves had no seal on them. The result here is bad and erratic compression and a poor running 630. To top it all off, one of the exhaust guides had been broken off of the head and was bouncing around inside the valve spring. This was probably done when the guides were pressed into the head; more than likely it was cracked, and then it broke off during operation. The end of the story for this 630 head was that it needed a valve guide, a head surface job, and valves and seats that were mated to work and seal together, and to be assembled properly. Although I was just the ‘inspector’ as to what was wrong with this head, I’m sure the owner saw to it that whoever had redone the head did it correctly the next time.
Cylinder head No. 2 involves a 1939 John Deere H, belonging to Jeff Schmidt of Kaukauna, Wisconsin. Jeff is a subscriber of the Green Magazine and currently still farms 300 acres. This John Deere H still does all the hay raking on this farm, and Jeff wouldn’t have it any other way. The little H was getting anti-freeze into the right side or No. 2 cylinder, and Jeff decided to take it apart this winter and fix it. The cylinder head was disassembled, cleaned, bead blasted thoroughly, and then inspected for cracks; here is what was found. Picture 2 shows the John Deere H head disassembled and being magnafluxed for cracks. It was detected that the right side combustion chamber of the head had once before been repaired (welded) to repair a crack. I noted however that a crack had reappeared at the very edge of the weld repair, and this is probably the cause of the internal leak. The head was checked for straightness as shown in picture 3. I found it to be perfectly flat. The cracked area of the head can be seen in picture 4; note the black arrows…this is an area of any John Deere 2 cylinder head where cracks most often appear. Hot welding cylinder heads is a process involving kiln heating the complete head; welding the cracked area; and slowly cooling the head back to normal, and then grinding the welded area back to a normal shape. It also usually involves removing the valve seats to properly heat and weld the damaged area, and then installing new valve seats when done. After all of this is finished, a normal valve and seat job is performed as was mentioned in the 630’s case. The head was then reassembled. Disappointed as we both were to find a cracked head; I suggested at this time that the head be rewelded at a qualified machine shop. It is my thought that it is always best whenever possible to keep the original castings with the tractor. I am glad that a crack was found and a reason for the leak was realized. It would have been a real disappointment to have to do this job over again if the head still leaked. As for the head gasket in this case, picture 5 shows the H’s gasket with blackened areas (just as I spoke of earlier) to be the problem. As I also mentioned, the head surface was perfectly flat…so why does the head gasket show darkened areas? It was noted by looking at the block markings on the gasket that it had been installed up side down. Once again, head gaskets are meant to be installed with the smooth side toward the block, and the crimped fire ring toward the cylinder head. The little H will soon get a “re” reconditioned head and a new right side out head gasket…no more coolant in No. 2 cylinder. My thanks to Jeff Schmidt for allowing me to write about his John Deere H.
Finally, cylinder head project No. 3 involves a John Deere 420. The head came to me (once again) wrapped in rags with the following instructions; do a valve job on it! The exhaust valves were both leaking, and the owner had detected some coolant coming out of the muffler on start up. Once again, the head was disassembled, cleaned, bead blasted, and then magnafluxed. THIS TIME, no cracks were detected, BUT the head showed .004 warpage. The exhaust seats showed severe wear and pitting, and would have to be replaced as would the intake seats. Valve guides to valve stem wear was excessive and in need of new guides. The intake and exhaust valves had been ground before and were worn too thin on the margin to be reused. When coolant is present in a combustion chamber and the tractor is run that way for any length of time, it tends to pit the exhaust valve seats, and severely erodes them as is shown in picture 6. Here too, the head gasket had blackened areas…and yes, you guessed it; while once again checking the block to gasket markings, it was found that the head gasket had been installed backwards. Even in the I.T. manuals, under any cylinder head section, it states which way the head gasket must be installed. If you aren’t sure, and the gasket is not marked, chances are it will be installed the wrong way. Remember…smooth side to..........
Too read the rest of this article, see Green Magazine's March 2010 issue.