I have approx 150hrs on the overhaul on my 1994 B7100HST. The engine was overheated by the previous owner and I didnt find out about it until after I purchased the tractor, thus the reason for the overhaul. While doing the overhaul I replaced all gaskets, rings, and 1 piston (middle cylinder). It runs great and has great power. I have started noticing some smoke coming from the blow-by tube in the last 50 or so hours and it is using a little oil. It seems to have been getting progressively worse. I did a compression check at operating temperature and got 355@#1, 305@#2, and 395@#3. I also rechecked the #2 cylinder after adding approx 1tsp of oil and it increased to approx 375psi. I also honed the cylinders during the overhaul and inspected them for any damage, of which i found none. The cylinders still had the factory cross hatching. At the time of the rebuild the tractor only had approx 470hrs. Can someone give me a little insight on the situation?
B7100 compression question
- Thread starter firehart2
- Start date
It doesn't appear as if #2 is sealing as well as well as #1 and #3 are. I don't suppose you checked bore inside diameters when you replaced that piston?? It may be out of round --- may never seal completely. Actually, compressions are reasonable even with #2 on the low end of acceptable. I would guess that's the origin of your blow-by. If it were me, I would ignore it all and run it. Just watch it --- a little blow by won't hurt anything. Just keep the oil fresh.
No i didn't mic the bores, but I would figure that it would've started the blow-by right off the bat if the cylinder was that far out of round. Like I said, for the first 100hrs or so it ran great and the rings seemed to seal right from the start. Just got me flustered as to why it would start doing it now.
So, what caused you to decide to rebuild it when you learned that it had been run hot?? What problem did you figure that created?
If the cylinder in #2 was not quite perfect the rings will initially seat and everything will seem copacetic but the rings will wear quite fast. Hence the seemingly good overhaul but the blowby is an indication the rings are on the way out. I have seen this many times with cheap overhauls.
By design, the cylinders can be bored twice without re-sleeving. You'll have the block out no matter which way you go. First step would be to check each bore and see where they are against the spec and see if they're out of round or not.
P.S. I think it's twice ----- verify that.
P.S. I think it's twice ----- verify that.
aquaforce
New member
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L245DT FEL, JD450 Track loader, 5' scrape blade&mower, 5x10 trailer, Dump truck
I think there is more to that cylinder than meets the eye. If a piston had to go then the bore most likely suffered some too.
You might do a freshen up with boring/pistons and high quality rings and do just fine.
My .02 cents
Did the tear down last night and found #1 piston to have a cracked ring land. I may have over looked it during the last rebuild. #2 looks fine and it had the lowest compression (go figure). I can still the the cross hatch marks in all three cylinders and they all look good. #3 piston looked good and tested out good during my compression check. Looks like I may just have it bored and throw in all new pistons and rings. Next stop is the machine shop.