Duff 206 #1 Posted January 30, 2010 Hi, folks, I started to tear down the M12 for 312-8 #2 not really knowing what to expect. When I got the tractor it had obviously been put outside and left for dead, although my good friend who found it for me said the PO had claimed it was a runner when he parked it. When I drained the oil there was no evidence of water inside, and it did have excellent compression - almost too good, if here is such a thing. I never tried to start it before tearing the tractor apart figuring I'd need to do some serious work on it eventually, which brings us to now. Right off the bat, one of the things I've learned here is to RTFM (translates to "read the freakin' manual" for those not into acronyms) before blindly jumping into things like tearing down engines, so I downloaded all 152 pages of the Kohler Service Manual and put it into a ring binder. Newbies, please hear me: the download may be a bit of a PITA, but the information and guidance in that manual is great! To the engine itself. Much to my surprise and great delight when I pulled the head I found the inside of the cylinder spotless - no scoring, no discoloration, and no ridge at the top of the piston travel. When I got a good light I could see very faint cross hatches on the cylinder walls from honing indicating that someone at some point, and probably not too long before putting the tractor down, had at least had the short block rebuilt. That probably also explains why the head bolts were way too easy to loosen up. Whoever did the rebuild probably didn't retorque the head bolts after the first run cycle. The head gasket popped off very easily and fortunately didn't show any signs of burning or blowby. Although I have a new one on the way, I think I'll keep this one in stock just in case I blow one and need one on short notice (I've got 3 M12 motors). The valves are incredibly clean as well, and the seats are very clean and even. No pits, erosion or discoloring from high temps. Same with the valve stems and springs. Aside from some minor carbon build up, the top end of the engine is in really nice shape. A little work with a stiff tooth brush and a plastic bondo spreader while keeping things clean with my shop vac and all is well. The "too good compression" turned out to be the valve lash on the exhaust valve having been set way too sloppy so that the ACR didn't lift the valve on the compression stroke. Turning by hand I can see the lifter raise at the right time in the cycle but it just barely contacts the valve. I'll deal with that tomorrow. Oh....my question. Nearly forgot! After I wire brush the cooling fins on the head I'd like to apply some engine paint to keep them from corroding again. Does aluminum need to be primed with anything special, or will any good quality high temp paint stick to it? I'm sure I'll have more to ask as I plow through this project, but I've tied up enough space here for tonight! Thanks loads for any replies! Duff :banghead: Share this post Link to post Share on other sites
Horse Fanatic 51 #2 Posted January 30, 2010 Duff, if you get the metal clean and free of grease, just paint will be fine. Good news on the engines internals! Share this post Link to post Share on other sites
Confused99 2 #3 Posted January 30, 2010 Personally, I would leave the aluminum bare. It will help with heat dissipation. Jason Share this post Link to post Share on other sites
Duff 206 #4 Posted January 30, 2010 Personally, I would leave the aluminum bare. It will help with heat dissipation. Jason Thanks for the info, Glenn, and Jason, I am sort of leaning toward leaving it plain for just that reason. Is there any way to slow down that white powdery corrosion/oxidation-type effect I see on the head? Part of it may have come from the machine having sat outside uncovered and unused for quite a while before I got it, although my #1 312 which I keep indoors and dry is showing some light oxidation/corrosion as well. Maybe it's just one of those things that bugs the h*ll out of me but really doesn't affect the condition or life of the tractor, and most of it is actually covered by the cooling tins. Duff :thumbs: Share this post Link to post Share on other sites
TT-(Moderator) 1,162 #5 Posted January 30, 2010 Painting the cylinder head can't be all that bad, Duff.... the engine manufacturers have done it for years. (and so have I) If you don't paint it, you can spray it with WD40 occasionally to slow down the oxidation, but it will eventually cook off anyhow. The fact that the head tin covers all but the edges of the fins and the muffler will be right in the way might make that a tough job though. Share this post Link to post Share on other sites
sorekiwi 761 #6 Posted January 30, 2010 WD-40 works great to stop aluminum getting the "fuzzies", and will also stop the head bolts from going rusty. If you spray it on while the head is warm it seems to soak into the aluminum pretty well. If you are repainting the shrouds etc though, I'd leave it a while, WD contains solvents that might screw up the fresh paint... Share this post Link to post Share on other sites
Confused99 2 #7 Posted January 31, 2010 Painting the cylinder head can't be all that bad, Duff.... the engine manufacturers have done it for years. (and so have I) I am trying to think of an engine that had the aluminum head painted and can not think of any. Which engines have you come across that have the head painted? Thanks, Jason Share this post Link to post Share on other sites
rick 257 #8 Posted January 31, 2010 Without going outside and looking, I can safely say the heads on a K161, a K241, and a Briggs 11HP are painted. I think on the newer engines the heads are not painted, nor the aluminum blocks. Share this post Link to post Share on other sites
TT-(Moderator) 1,162 #9 Posted January 31, 2010 Just about every Briggs & Stratton flat head engine built from way back in the beginning up until the 90's had painted heads, cylinder fins, etc. I think they quit painting them (blocks and all) to save money - not to help with cooling. Kohler, Wisconsin, Clinton, and Tecumseh engines used to have everything painted - including the spark plug and wire. Once the manufacturers started installing all of the extra cooling tins, a lot of the surfaces were not painted just because the paint couldn't get to them. Keeping the flywheel screen and cooling fins clean is more critical than having a thin layer of paint on the fins. It's also very important to operate these engines at or above 3/4 throttle to insure adequate airflow. Chugging them around at idle on a hot day is an invitation to failure. Share this post Link to post Share on other sites
Confused99 2 #10 Posted January 31, 2010 Yeah, now that you mention it, I can remember some painted engines. You are probably right that the main reason for not painting was to save some $$$. Jason Share this post Link to post Share on other sites
rickv1957 75 #11 Posted January 31, 2010 Jason,looking in garage the only cylinder head I see not painted is the onan on a 520,Rick Share this post Link to post Share on other sites
linen beige 15 #12 Posted January 31, 2010 Which engines have you come across that have the head painted? Every Kohler K series I've ever seen. every Briggs I've owned, every Lauson/Techumseh I've owned,.... Share this post Link to post Share on other sites
Duff 206 #13 Posted February 1, 2010 Thanks, guys, for all the replies. Educational! I've sort of compromised - after a thorough cleaning I painted the block but not the cooling fins on the cylinder jug (they're pretty much invisible behind the tins and the muffler anyway), and I'm going to clean up the head and leave that natural as well. The tins are in great shape but I'm going to give them a quick spray to match the block (gloss black). Should get my gasket set this week, then reassembly and hopefully a running engine! This project was going too smoothly - when I went to pull the main drive pulley so i could clean behind it for paint I managed to break a chunk out of it . Newbies - word of caution here: do not succumb to temptation and think you can "gently" pry the pulley loose (even with both set screws backed out) by using a big screwdriver between the pulley and the block. The result ain't pretty! Beg/buy/steal/borrow the appropriate puller! Anybody got a spare 7466 drive pulley they'd be willing to part with? (Oh - TT, thanks again for the template for the tool to hold the starter brushes in place for reassembly - worked slick! Duff :banghead: Share this post Link to post Share on other sites