Chat6155 3 #1 Posted October 7, 2013 Hello all. Going along with my 1st Kohler rebuild and came up with a few questions I'm hopeing that the learnered here will be able to impart some guidance on. 1st, while glassbeading the head, I found what appears to be an eroded away area on this corner of the gasket mating surface around the exhaust valve. As you can see in the pictures, the area from the inside of the head bolt bore to the combustion chamber is fine. Was just wondering if it's good to go or should I replace it? Right now, only planning on doing the Figure 8 on the glass covered 600 wet to even the mating surface out. If it's any help for diagnosis, a: 2 pictures of the piston that came out of it. The eroded area on the top edge was towards the valves. The rest of the piston had normal wear. I'm assuming that this may have been caused by pre-ignition. b: Also, just came from machine shop and he told me the exhaust valve seat spun when he tried to do the grind. And, the exhaust valve stem was tapered from about 2/3 of the way up to almost the bottom of the head. c: The little bit of crud you can make out in the head bolt bore is the only one. All the other head bolt bores were clean. 2nd question. While cleaning the Kohler carb [has the main adjust needle just behind the throttle], I discovered a very small orifice [12 o'clock in the picture]. Can anyone identify it for me? I tried following the casting on the outside, but that didn't go very far. I know the other orfice [about 1 o'clock] is the air bleed for the idle mixture screw. It would be helpful to know as I want to blow air through it to ensure it's clear, I just don't know where the air is supposed to come out at the other end. Thanks in advance. Share this post Link to post Share on other sites
Fordiesel69 263 #2 Posted October 7, 2013 That piston is no longer usable with the errosion you have. This is caused by the engine not being decarboned at proper intervals, in addition to a ridge forming at the top of the cylinder bore. Kohler says 500hrs, I say 250hrs max and I will be starting another thread explaining why with pics. If you can spare the extra cash, go with a style d piston and narrow rod. You will have better oil control, and most important, less bore wear over the life of the engine. The style A pistons oval the bore out, and being the rings are thicker, creat more wear. The machine shop will need to install a new valve seat and guide, as well as the valve itself getting replaced. Quite common for those to loosen up on a high hour engine, but it is not normal for the seat to loosen up. As for the carb, not sure. Share this post Link to post Share on other sites
KATO 115 #3 Posted October 9, 2013 Without seeing the whole engine its all a guess of course, but it looks to me like you had a blown head gasket likely caused by a severely overheated engine. Which would also cause valve and seat problems AND piston damage. piston looks like the material was torn away rather than eroded due to expansion in that area, as it is where the combustion chamber is. Hard to say if there was any preignition without seeing the rod and crank as it will usually show up on the rod bearing surfaces and crank. Could have been as simple as clogged fins etc Share this post Link to post Share on other sites
Chat6155 3 #4 Posted October 9, 2013 The head gasket didn't look bad / damaged or blown when I disassembled the engine, but this is my 1st Kohler, so maybe I wasn't sure of what to look for. In addition to a new con rod, when I pulled the pistonand saw the damage, I wrote that off too. The machine shop confirmed a new piston purchase in that the block needed an over bore of .010". In addition, after cleaning up the crank throw, the machine shop saved it by turning it .010" under. Both valve seats and guides were replaced, in addition to the valves also. The previous piston and partial con rod now hold the honor of paper weight. Again, my 1st Kohler, just trying to learn. Without seeing the whole engine??? Hear ya go... Share this post Link to post Share on other sites
WH nut 553 #5 Posted October 9, 2013 Looks like it starved for oil and it got hot. Share this post Link to post Share on other sites
Chat6155 3 #6 Posted October 9, 2013 Story goes that 2 PO's ago was using it for snowblowing on a 312 the winter of '12-'13 and was a bit tardy on checking the oil. PO was going to strip it for parts, but I picked it up complete just to rebuild it because I hadn't done one before. Luckly, inside of block, cam, tappets and govenor were ok. Rebuild kit should be here by the end of the week and I'll get the piston to the machine shop for final bore and hone Monday. Hope to have it up and running not too long after that, if time allows. Share this post Link to post Share on other sites
KATO 115 #7 Posted October 10, 2013 OUCH ... THAT WOULD XPLAIN ALOT Share this post Link to post Share on other sites
Fordiesel69 263 #8 Posted October 10, 2013 Don;t use the cheap china points that come with the kit (if it does). They will last 1-2 hours and crack. I clean the original kohler points and keep using them until they go bad. Are you going to put the balance gears back in? Share this post Link to post Share on other sites
WH nut 553 #9 Posted October 10, 2013 I have used the Cheap China kits/ Sterns in several motors and haven't had a problem. I was also told my an Old Wheel horse dealer years ago to always replace the rod if you changed pistons or rings. He said the rods get brittle and the extra force from new rings would cause the rod to break. I have experienced that Share this post Link to post Share on other sites
Chat6155 3 #10 Posted October 10, 2013 Wasn't aware that the new points could possibly be low quality imports, thanks for the heads up. Is there any way to tell? The existing points are just about burned away, so they're out of the equation. However, the condenser tested good. Was going to hold on to that as a spare. Any measurment I should look for on the fiber pin that activates the points, or is wear generally minimal on that? New rod comes with the kit. Will polish off the casting flash [i know, I know...it's not going into a Camaro or Vega driven by Grumpy Jenkins, but just for piece of mind]. Balance Gears; nope...after all I've read about them here, they, along with their clips, spacers, shims and the pins they rode on are now contently resting in a coffee can in the garage, probably never to see the spray of oil again [will fill the pin holes with 1/2" freeze plugs]. If worst comes to worst, I'll mount the engine on Isolator mounts. But, as of now, the engine has no 'equipment destination'. It's just a rebuild for the sake of self-induced learning. Share this post Link to post Share on other sites
