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Thread: 1974 XS/TX650 rebuild

  1. #231
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    Oct 2015
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    th62's Tools
    In searching through this thread trying to find the above picture, I noticed I'd never posted on the engine build. A little late but here it is.

    I never bothered trying to start the engine when I bought the bike home, waste of time considering what I was intending. After getting the engine out of the bike, by no means an easy task, I got it up on the bench with a lot of effort, this is one heavy engine, 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 did an oil change without cleaning the filters

    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 and floating around in the crankcase. 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 and a couple of bases for the valve springs which were missing, 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.
    Jap bikes are just so easy to assemble: invert the top crankcase chuck all the gears in, line up the mains pins drape the cam chain over the centre crankshaft sprocket, tie the ends together, load the crankshaft in, paint the mating surfaces with goop and bolt the lower case in position.

    I then made up a bench stand, mounted the lower end in, assembled the ring 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 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 has mangled JIS heads so I binned them and looked for some new ones. Hang the classic sign on a bike and parts prices go through the roof, the buggers wanted $40 for four. 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 cleaning the strainers, filling with oil and turning the engine with a cordless drill to get oil circulating .

    Rather than start the engine up on the bench stand and watch it vibrate across the bench and fall on the floor, I built a new stand on wheels, 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. Damn thing roared into life immediately and damn loud with those pipes. If you think Brit twins vibrate, this thing leaves them for dead, I had to tie it to the bench grinder stand to stop it walking around the shed.

    I made up a manometer and synced the carbs, then stood back and looked at it. Nope donít like it, too bland in silver. So, up on the bench again, rip it apart, blast the paint off and repainted it black, then do it all again. Much, much better.
    Attached Thumbnails Attached Thumbnails 1974 XS/TX650 rebuild-bought-left.jpg   1974 XS/TX650 rebuild-damaged-crankcase.jpg   1974 XS/TX650 rebuild-damaged-shifter-drum-mount.jpg   1974 XS/TX650 rebuild-left-cover.jpg   1974 XS/TX650 rebuild-oxidismed-right-cover.jpg  

    1974 XS/TX650 rebuild-3.jpg   1974 XS/TX650 rebuild-blasted-cases.jpg   1974 XS/TX650 rebuild-6.jpg   1974 XS/TX650 rebuild-blasted-carbs.jpg   1974 XS/TX650 rebuild-enggine-disassembled.jpg  

    1974 XS/TX650 rebuild-barrel-head-rocker-carbs.jpg   1974 XS/TX650 rebuild-engine-casses-carbs-painted-assembled-right.jpg  

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  2. The Following 2 Users Say Thank You to th62 For This Useful Post:

    Frank S (Jun 12, 2022), Rikk (Jun 13, 2022)

  3. #232
    Supporting Member IntheGroove's Avatar
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    It sure was worth the effort...

  4. #233
    Supporting Member Frank S's Avatar
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    Aug 2015
    Peacock TX
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    Frank S's Tools
    Looks like you have done an outstanding job on your rebuild, the engine looks better than new
    Never try to tell me it can't be done
    When I have to paint I use KBS products

  5. #234
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    th62's Tools
    Painted the tank, seat, guards, headlight and callipers with 2k clearcoat this morning. Unfortunately, I can't wear glasses under the respiration so I couldn't see too clearly - bloody great run on the tank, damn. Couldn't get any non isocyanate free, so just the usual 2K.

    It's been over 40 years since I used 2k, so I couldn't remember what coverage was like, how much paint I'd need, googled it in various painting forums. 2litres minimum for frame, tank, guards seat, headlight I was advised. Armed with that knowledge, I shyed away from 2k because it would have cost near as damn it to $450/$500.

    Seems our painting professionals haven' a clue., I mixed up 250mm clear, 125mm catalyst and a little thinners. Got three coats down on tank, guards, seat, headlight and callipers and still had 200mm of mixed paint left.

    By the look of it, I won't be spending anytime compounding or polishing the paintwork.

    This pic should give you some idea why painting and, polishing aren't my favourite past times. Scared the crap out of the dog.
    Attached Thumbnails Attached Thumbnails 1974 XS/TX650 rebuild-win_20220623_14_21_41_pro.jpg   1974 XS/TX650 rebuild-win_20220623_10_06_26_pro.jpg  

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  6. The Following 3 Users Say Thank You to th62 For This Useful Post:

    asterix (Jun 23, 2022), Rikk (Jun 23, 2022), tonyfoale (Jun 23, 2022)

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