My 73 Yamaha TX750 Rebuild....

Hey look, another horribly conceived, poorly planned, unfinished chopper project.

Are two totally different engines. I had a TX750 back in 1978. Had 22,000 miles on it when I got it, engine sounded like a cement mixer at idle, better at speed. Totally false myth about the lack of cam chain tensioner, it's there, right in the middle behind the cylinders. The BALANCER chain had no tensioner and was later retrofitted (but many didn't make it in for the free upgrade). The electric starter drive clutch would expire early, mine worked somewhat. The oil and air filters were over engineered and STUPID money to replace them. The points would foul with oil that leaked out through the shafts seal.
I find now from research that the biggest issue was the dry sump oiling system was flawed, inasmuch as sustained high speed running would aerate the oil as it flowed over the two balance shafts, and foam is bad for the plain rod bearings. 1974 saw a deep sump added (again, retrofits were available for '73's) but it was too late. Dropped mid year from the line-up. My '73 made 63 hp and handled what I thought was great.. Conti twins and a single disc brake! I NEVER lost a game of grab-ass to ANY British twin, (American twin either, for that matter) but was obviously outclassed by the multis that were becoming common.
Back to the here and now, I've got another one I want to try and run... anyone with any parts or parts bike I'd like to hear from. TIA

on my latest TX750... the carbs were the worst I'd seen, scraped and cleaned, poked and prodded, wired, polished, replaced floats (corroded THROUGH!) and regasketed until they were usable. Fuel tank was varnished bad, but little rust. Cleaned up nicely with the 1/4" square nuts and solvent, then dishwasher soap. Fuel petcocks were corroded through, cleaned, JB welded, new rubbers. Compression was hard to check, rings probably stuck. Points burned, spark on one side. I dealt with all that and changed the oil twice to fluch the nastiness out. I fired it up two weeks ago. Runs great, compression measures 170 and 175! (warm) I ran it warm and dumped the oil. Last week I ran it again (to get the StaBil worked into the carbs.) and decided, what the hell... I rode it up and down my (very rural) street a couple times. It runs strong, pulls good, clutch and trans function well. Tires, chain and sprockets and wheel bearings are in the mail, soon it will be a runner!

In addition to having some real design issues, they leaked/used oil. I suspect many blew for that reason.... didn't get topped up properly

This might be just folklore, but I once heard that Yamaha actually dispatched a squadron of technicians from Japan to the U.S. just to go around the country and repair TX 750 models. If that story isn't true...it oughtta be!

I worked in a Yamaha shop in 1973.

When new, the TX750 was a very nice motorcycle. We had a demonstrator, and I rode it alot. Smooth and torquey, with a very nice seat. I thought it was nice looking, too.

The 1973's did have a defect. The crankcase was porus in the area of the timing cavity, so oil would seep in & destroy the points. Yamaha had a recall on these, and were SWAPPING CASES on every one they could get back.

With this recall, their reputation was ruined. Yamaha had a tough time selling the 1974 TX750s, even though the defect was fixed.

I also heard that they would froth the oil in extended high-speed runs, and blow up. I've never seen one do this, but my sample was quite small.

Tom in Salem

besides tobyfolwick? I'm really looking for the original handlebar bend.. or a description of such.

Here it is as dragged home:


And then after being made roadworthy.. paint to come next winter

looks nice beside the goofy looking handlebars....

[FONT=&quot]I also worked at a Yamaha dealer when the TX750 was introduced, it was Yamaha's flagship, glorious in it's original metallic gold. The one sitting in our showroom came with a large box of engine parts to be installed before being sold.

The omi-phase harmonic balancer had no provision for balancer chain adjustment, a kit was provided with an eccentric shaft and locking system.
After about 3000 miles the weights started wearing the sides of the cases and we tried to remedy this by added 4 small radial bearing.

The main oil gallery was behind the points, oil constantly leaked into the points compartment, we changed the seals several times. Yamaha sent us a new style labyrinth seal, didn't stop the oil, eventually they suggested that we drill a small hole in the case to prevent accumulation fouling the points.

The engine had double cases (cosmetic covers to hide the functional engine cases). An exhaust crossover was part of the cylinder head needlessly the engine ran very hot, the oil temp was at the upper limits of normal motor oil (not sure I think about 270 deg.F). Yamaha added a sump extension. Oil capacity was close to 5 quarts.

There were some strange electrical issues, a contact was imbedded in the rear brake shoes to light a brake wear indicator on the dash. There was talk of this current "bleeding" back into the electrical system and engaging the starter, this could happen at any time/speed. I did see a TX750 with the crankshaft protruding out of the front of the engine.

Sorry, I'm not trying to put the bike down, just an old fart who thought they were pretty cool just brought to market too soon.

I remember holding one WOT going down a grade, the speedo was reading 128mph.

Ken
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lol, and this 16YO stunt pilot held that bastid WFO on I-495 for miles as well.. I remember 120 indicated.:eek1

I bought one new, Yamaha left me hanging. I've had a lot of new bikes since then, no Yamahas.

I really like that bike too, it ran and rode well.

And as she stands today...

Great work! Though I'm scared to get involved with one of those, I sure like the way they look and would love to take one for a ride.

I think I saw your bike today in North Brookfield. If that was it, very nice work!

Thanks, It was there. First outing. Rescued at the Bettencourt auction. Didn't see another one, LOL

Very nice indeed. I loved the way Yamaha painte dthe bikes in the 70s. I worked for a local dealer when they were new, in the mid 1970s until about 1978. I loved the Yamaha XS650 and the TX series and until everyone at the shop ragged on the TX750, I thought I wanted one. But I had a Daytona RD400F and since it was faster, and so sexy looking, I never got a TX750.....Beautiful work and hope it lasts forever. I hear riden as they should be they can be quite reliable.

a few pics from www.rice-o-rama.com
here:
http://s1040.photobucket.com/albums/b404/gsx800ho/Motorcycle stuff/Rice-O-Rama 2011/

We rode the slab for 60 miles in the morning because we were in a hurry... 75-80mph, no worries, sounded, felt great. I had dropped two teeth on the rear sprocket and up one on the front for longer legs. The Amsoil 20-50 makes the clutch a bit grabby, but the engine protection, it's a minor inconvenience.

I picked up a very ratty 1973 TX750 out of the junk yard last fall. Someone had given it a funky rat / cafe treatment sometime in the past and it had a cool rusty look to it so I stuck it in the window at the shop. Things slowed down over the last couple days so I put in on the lift to see what would happen. Cleaned the carbs, checked the timing and threw on an aux tank. Wiring was hacked so I put 12v straight to the coil. Scared the cramp out of me when it actually fired up and ran.

I think it has the extended oil sump and I'll check for the hole at the points case (no evidence of oil though). I'm hoping to find the adjustable chain for the balancer. I really didn't expect it to run so now I'll look a bit more carefully. It should be a fun shop bike