Sudden Excessive Blow By

[hrtull]

Very Excessive Crankcase Blow by.

YM 186 D with Yanmar 3T72HA engine. Purchased this tractor about 2 years ago and refurbished it. I posted the rebuild on this site under Tractor Projects( YM 186 Build). Tach time indicated about 800 hrs. I have used it about 30 hours with no issues. Starts well in cold weather ( never used starting fluid), leaks no oil, runs fine and plenty of power until a few days ago. Temperature was about 40 degrees in Ohio. Usual start up is switch to glow for a few seconds, decompress and free spin for a few seconds and then engage compression and start up never an issue.
This time however it was very hard to start and needed extra battery boost to do so. After starting I let it warm up for about 20 minutes,engine seemed to tun fine but then I noticed crankcase vent hose blowing excessively and starting to drip oil from it. I then took off oil filler cap while engine running and air was gushing out heavily. It had enough pressure to lift the fill cap off after unscrewing.
I then started researching everything regarding excessive blow by. Stuck rings, broken rings, worn rings ,damaged pistons, blown head gasket , cracked head and just about everything else. I realized engine would need inspected. I removed head and all seemed to be in order. Head gasket good (anti freeze clear and no oil). Valves and all valve components appear good. The one thing that really got my attention was when I hand turned the crank to look at piston action the center cylinder sleeve came up with the piston upstroke. I could easily push it back down. After watching many videos of people struggling to remove sleeves this seems not right. I stopped at this point and will remove pistons tomorrow. Before stopping for the evening I added about an inch of rubbing alcohol in each cylinder and it appears to be holding. My question, could this loose sleeve /bad sleeve O ring be causing blow by and such a high crankcase pressure. Also the piston tops looked good as well as interior sleeve walls. The cross hatching appears to be even wear. Any help or advise greatly appreciated, Thanks HRTULL

[winston]

Wow, hard to understand just what has happened. No doubt your crankcase blow by tells us a lot of compression going into the crankcase. Reading your post about the loose liner would tend to indicate that is the cause. However, I am trying to understand how the liner could move with the head setting on it, but then, maybe it didn't move. Your liners do not have o-ring seals. I believe you have what is called dry liners. https://www.hoyetractor.com/PROD/DS-72.htm

Bottom line thought from me is the problem is involving the loose liner.

Back again with a couple of pages from the 169 service manual, basically same engine as your 186.

[hrtull]

Winston, Thanks for the liner information. It does state that the liners are set by hand and removing requires no special tools. So I guess it could be normal. I am puzzled how much blow by could exist even if loose. Like you said the head holds it in and all of that looked good. I thought upon removing the head that I was going to see a very obvious problem. I thought after adding alcohol that one of the cylinders would quickly drain down and didn't but I am probably under estimating how that can change with a hot engine and high compression. I am going to drop pan and remove pistons today hoping to find the obvious problem. I will post my results. Thanks again, Harmon T

[hrtull]

Found the problem. Broken piston flange on front cylinder (A). Going to replace piston and add new rings to the other 2 good pistons. Lap the valves, new head gasket with all other require gaskets and reassemble. A minimum repair but everything else in good shape and before this broken piston it was running perfect with no oil consumption. Thanks, Harmon T

[winston]

Sounds like your on top of it. Let us know when she is running fine again.

[hrtull]

I got this engine reassembled. Installed the new piston and added new rings to all 3 pistons. Lapped the valves and reassembled . Cleaning the old head gasket was probably the longest one thing, lots of razor blades and WD40. I gapped the valves, purged the fuel system and it started right up. Do I need to do any special break in. Thanks and have a great day, HRTULL

[winston]

Only an opinion on my part. I would use as normal.

[hrtull]

Winston, thanks for all your info and help., HRTULL