74 TX650 rebuild and pretty up.

toglhot

Active Member
The 74 TX650.was in a pretty crook condition when I bought it: Every nut and bolt was rusted, aluminium was badly,oxidised admitted, and it looked lime the only tools the POhad were a hammer and chisel. After getting the engine out of the bike I got it up on the bench and started stripping it.
In pulling the engine apart I discovered the previous owner had installed a new set of rings on a bore and pistons that were way out of spec, bodged up an auto advance unit that was 80 degrees out, elongated the points backing plate slots to allow for a stretched cam chain, put a kit through the carbs without bothering to clean them and the two oil filtrs didn't look like they'd ever been cleaned.
I knew the top crankcase had been smashed by an errant chain, unfortunately, the damage was a bit more extensive, the chain had ripped the alternator cables and the shifter drum bearing housing was also damaged. I stripped the motor down and found the piston to bore clearance was way out of spec, the valve seats were badly pitted, the cam chain was stretched so much the motor couldn't be timed, I noted the previous owner had extended the slots on the points backing plate, but still there simply wasn't enough movement in the backing plate to time it.
Rather than buy a new auto advance unit, the previous owner had bodged up a replacement, it put the timing out by around 80 degrees. The cam chain guides had delaminated leaving bits of black stuff hanging off the aluminium base guides. The shifter drum was missing a pin, so no hope of getting any gears. Sump and side filters were so gummed up I'd be surprised if any oil actually got through them. All the JIS headed screws were absolutely mangled, the eight chrome rocker dome nuts were rusted as was the oil pipe, engine oil seals were all buggered the springs behind the lips on some had actually popped out.
The barrel gasket had developed a serious leak at some time but had never been seen to, drive sprocket looked like a series of hooks. The sprocket nut had nearly been cut in half by a chisel, side covers were badly pitted and oxidised. Carb float chambers were gummed up and pitted on the bottom, manifold rubbers were split. Luckily there were no stripped gears and the Crank and associated mains, conrods and so on were all in good condition. A feature of these bikes is the bullet proof crank.
I bought some new, second hand cases, had the barrel rebored and valve seats reground, bought two new pistons plus rings, gudgeons and circlips, made up a pin for the shifter drum, bought new gaskets and seals plus a stainless Allen head kit, bought a new auto advance unit, had the point and advance covers, rocker domes and oil pipe re chromed.
I blasted the crankcase halves, barrel, head and rocker cover and carb bodies, then pressure cleaned everything several times making sure I got rid of all the blasting media from all the orifices and nooks and crannies, then soaked them in a bath of degreaser and pressure cleaned them again a few times then blew everything out with High pressure air.
I smoothed over all the casting flashes on the crankcases and painted them silver, squared up the cylinder head fins and removed any casting lumps. The side covers were blasted inside and the outsides were polished along with the valve covers, breather box, dipstick, cam chain adjuster and carb tops and float bowls.
I pulled the starter motor apart and found all in order, so polished up the aluminium ends and painted the body Black. The starter gear spring gave no tension on the gear so I reshaped that a little.
 

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I then made up a bench stand, mounted the lower end in, assemble thecrank and gears, assembled the rings on the pistons and inserted the pistons in the bores then lowered the barrel over the studs and inserted the gudgeons and circlips and finished lowering the barrel.
The head was missing a couple of valve spring base washers, so I made a couple of new ones and mounted the valves then lowered the head in place over a new gasket. Next came the cam which I put in place, draped the chain over and timed the cam then riveted the chain together.
Next came the rocker cover. After assembling the rockers I lowered the rocker cover over the studs and torqued everything down. The rockershaft end caps had mangled JIS heads so I binned them and looked for some new ones. Too expensive at $40, so I looked on ebay and found some short, stainless, Allen heads M18 x 1.5 for $1.20 each for an all up price of $5 and installed them.
Carbs were blasted then pressure cleaned and blown through with air and reassembled and bolted in place on new rubber manifolds. Clutch, starter gear, and alternator were all bolted in place and I was ready to start it up. First filling with oil and cleaning the strainers, then turning the engine over with cordless drill to get the oil circulating..
I built a new stand on wheels mounted the ngine, added a fuel tank bracket, mounted the regulator, condensers, a couple of Bosch coils, a Honda solenoid, installed a $4 ebay three phase rectifier (used OEMs are $70) wired everything up to a rocker ignition switch and momentary starter switch and pushed the start button adit roared into life immediately and vey loudly with those straight through shorty pipes. I had to tie the stand to the bench grinder stand to stop it walking around the shed, these things vibrate.
 

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Next I made up a manometer and synced the carbs.
stood back and looked at it, nup didn't like boring in silver. So the engine was back up the bench.
 
After strippingnthe engine again, I removed all the silver,paint, painted everything black, gave the ally another polish, cut the threads off the pressure plate screws, drill though with a 6mm bit and fitted them with Allen heads. The sump filters on these things, tend to blow out over the end where the filtering media is straight, so I fashioned a guard over the end of the filter and fitted that.
Previously I'd fitted barbs to,the manifolds for syncing, so then Imade a better manometer using the two30mm lengths of acrylic tube. I cut four platforms made of ply, fitted two either end with a neoprene gasket between and clamped them together with three lengths of alltread.
 

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