I know this is an old post but these 1625's seem to go forever, getting older and more worn but still chugging along and fairly low on purchase price. I got mine, no hour meter, no Kohler sticker (should have known better but I was enthused) for AUD$9000. Nearly every bush was worn and the seatings ovalled. Rather than wait for spring steel tension bushes from the States (1" id, split, 1/2" wide) I just replaced them with hardened steel plain bushes with JB Weld to take up the oval. Seems ok. They were a bugger to cut, had to do em in lathe with a 1mm grinder cut off wheel; very messy. Quarter the price of OEM.
The Kholer 25hp was still chugging but smokey and leaking oil from the crankcase gasket. Stripped one pot. Valve stems worn. Cylinders down to within .005 mm of maximum wear (original 20.00-20.025mm, max wear 20.038). But cylinder was not oval and not tapered, just worn out top to bottom evenly. Very impressive Mr Kohler. Junked that and fitted a 1000cc 33hp Chinese motor from jonno and johno Ballarat Australia. Similar (the same?) to GB1000 in the States. I see that GB1000 advertised as 37hp but I reckon it's a furphy. Maybe 35hp if it's injected but only 33hp if vanilla.
It fitted very well. The PTO was the same diameter and length and the same height above base as the Kohler. The outer mounts slipped straight in although I had to lengthen the slots backwards by about 10mm to suit the belts that were on it. Inner slots I had to recut in the plate, drilling holes and angle grinder cutting joining slots.
Motor was still a little bit close so I trimmed the hydraulic pulley by 5mm and cut a more generous inner fillet. The Chinee motor has a slightly larger fillet than the Kohler on the PTO. Results that the clutch and pulleys are 5mm closer, so I had to move the big front pulley out on the new jackshaft by 5mm which means it now rubs on the front cover. Have to space that out by a coupla millimetres. Lucky I made the jackshaft a little longer, JIC I want to junk the HTD and try three B section belts on the cutter drive. Could have just slotted the outer engine mounts by 5mm but I didn't want to bugger up the warranty.
Turned up a new jackshaft out of 40mm truck brake S-Cam shaft and put on new pulleys from ptparts in Melbourne Australia. Quarter the price of OEM and I get British Taper Locks not those horrible QD Tapers that were original. Wondered why I couldn't screw the three bolts in to release the QDs. Found that over the years they had stretched and the threads were no longer accurate. Come on Rayco, surely the cost of hi-tensile bolts wouldn't break the bank!
Mitsuboshi 1190H 14M 40 and the Optibelt 1170 A sections were recent so they went back on. Since I don't have a manual and nobody on these sites seems to answer a straight out question I adjusted the HTD to 12mm on 6kg tension and the A sections to what feels right, about the same. Bando give song and dance about tensioning V belts but just say HTDs should be "not too tight and not too loose". Not terribly helpful Mr Bando. Just made up a spring with a bolt in the middle that would bottom out when the spring was compressed to 6kg on my kitchen scales. Seems to work ok.
I've only ground one medium stump so far and haven't pushed the new motor too much but everything seems to be hanging together. I'll post an update when it's done a bit more work and if anyone is interested, or even reads this old post, I'll put up some pics and a video I made.
