by 38racing » Tue Dec 26, 2023 10:43 pm
it's on an ariens snowblower with some history. dumpster dropoff few years back missing wheels. I cobbled some wheels.Memory not complete as it has what looks aftermarket carb that I may have installed. I remember that it started fine and ran except engine would die when it started to blow snow. Back then a forum suggested it was lack of clearance on exhaust valve. Indeed it was and when I ground to create clearance it ran and blew snow. But it's been sitting idle again, in shelter last winter. I decided to pull out this winter but cobbled wheel broke. got some better used wheels but when checking it over I noticed wheel drive belt riding on edge of large pulley instead of in groove. I found top and bottom pulleys out of line. To remedy this I removed bucket and moved big pulley forward and small pulley (on cam shaft) slightly inward toward engine. When I started the engine after this (started and ran fine) there was a clunking noise in the pulley area. When I engaged the wheel drive the noise disappeared. I repeated just a brief period and shut it down. I removed bucket and it was obvious that the mounting stud ends of the wheel drive pulley were now hitting those of the auger pulley. Since engaging wheel drive moves its pulley away from auger pulley the noise would stop. I proceeded to move pulley back a bit and cut off the mounting studs of both pulleys flush with the nuts. I replaced bucket. Now the engine won't start. It has electric start so rpm is good. (no pulley clunking when it cranks) At times it had a week fire from muffler but only as it stopped when I disengaged the starter. I checked spark. Jumps the 1/4 gap of that black tester. Has fuel. primes plus I try with carb cleaner. Compression 150 psi. Leakdown at 25 psi about 20% and leaks slightly at both intake and exhaust. So i get to thinking spark timing or valve timing. Verified flywheel key. Removing plug I see both valves moving and appear in time with piston. Also checked valve clearance. spec 8-12 thou. intake at 12, exhaust at 16 (bit surprised at that but maybe I over ground the stem way back). Then I think if wheel pulley, being driven by cam shaft, could have shifted crank gear driving cam. engine on bench now. I remove side cover. Crank gear is press fit so in theory it could shift. I set cam timing off by a tooth but in hind sight I think I went the wrong direction. No change. I did remove head to verify valves and seats. Timing 'seems' close as I get the valve overlap at tdc exhaust. While head is off I sprayed carb cleaner on valves and sent compressed air into intake. some leakage. I lapped the intake but I still get some leakage on that air test. So then I wonder if this is the old coil issue, good spark in testing, but not under compression. Anyway I have crank and cam timed back to marks on the gears, a different coil that again jumps the 1/4 " gap, the 3rd sparkplug (new ngk) , compression still 150 psi and it still just cranks with no fire, no backfire, just like there was no spark but the inline tester is sparking. There is air? fuel mixture? exiting muffler. Maybe I should hold a bbq lighter there? I'm baffled. I've reviewed my go karting stuff from 25 years ago and thinking of checking the centre lines of the cam to verify timing. I assume I could do same on another tecumseh engine for comparison. Wondering if cams are normally installed straight up in these engines. Any suggestions much appreciated. My wife's suggestion is that I have more important things to work on.