To those browsing this site: I am enclosing the text of 6 EMAILS from Bill Johnsen as he was working on his trio of TX750's. He provides a lot of insight into the innards of this complicated beast, plus has many helpful tips on repair that don't go "by the book". I asked for permission to share them and here they are for your reading enjoyment.

Roger Cole

P.S. These are the kinds of things needed to keep these machines on the road. If any of you can contribute along these lines, please write or email with your repair tips.

Date: Thu, 15 May 1997 08:44:22 -0600

I tore down the spare engine that came with the TX from Alfa. This is not an engine an inexperienced mechanic would want to work on. It's quite complex considering it's age. Yamaha must have spent quite some time trying to design the perfect engine. It's a shame they have such a bad reputation because it's an engineering marvel.

The local Yamaha dealer did manage to find some part numbers and prices but their prices are unbelievable. Considering that it's such a pain to take this engine out and tear it apart it would be wise to replace -! timing chain $55., balancer chain $104., valve guides $68., most gaskets $61., that's not including prices yet for bearings, pistons, rings and machining. This is not a cheap engine to rebuild.

Several days ago I passed a Yamaha dealer in Tomah, WI so I stopped and walked out behind the building where the treasures are kept and found another 74TX750. It's rough but $100 did the job and I have it at home. Has 40,000 miles on it. The electric start bendix is out like all the rest of them but jumper cables and a puff of ether fired it right up. The carbs are ill but the motor seems to run and sounds "OK". I'm sure it's a bit loose but will make for good spare parts.

Speaking of the starter it seems that everyone of these had bendix failure. The starter slips and makes terrible noises. The clutch grabs the housing on the starter sprocket and if this area is worn even .003 it will cause the clutch to slip. This part is suppose to cost a fortune but it would be easy to turn down and sleeve to the correct size if I would know the correct size. The Yamaha dealers I've called so far say they have no reference to look it up. I asked them to pull a new part and measure it for me but they would not.!

What we will do to fix up a strange old bike!

Thanks

Bill

Date: Thu, 15 May 1997 21:47:14 -0500
From: Bill Johnsen

Considering that all the TX750's were noted as junk, I now have two that run. The one I bought at Alfa was suppose to have a bad transmission. It certainly behaved like one considering no gears could be changed and the kick starter was stuck. I removed the right engine side cover and there was a small bit of a spring lying in the bottom. There is no place it could have come from other than the clutch. After removing the clutch springs, lots of little destroyed pieces fell out. The clutch had exploded and locked everything up. I made a tool out of the old clutch and tested the transmission. It shifts fine. The 1973 engine that I just tore apart had a good clutch and clutch basket so I attempted to assemble it. The cage that the clutch fits in has the gear that goes from the crankshaft to the transmission and the oil pump distributor wouldn't fit. It was about .016 too big. I removed the crankshaft drive gear and installed the one out of the 1973. My assumption was right. The crank gear and the clutch gear are matched sets. They are fitted to take up any excessive clearance between gears. There is a small number etched on the back which seems to be a code. This isn't covered in the manual. If you disassemble more than one engine, these gears stay together as a set. There may be situations where they would interchange. The manual also does a poor job of describing setting the timing from the crank to clutch to distributor gear. There is not any marks on the clutch basket gear to line up with the crank and distributor. The photo is the key of description.!

Well the right cover went back on, filled the carbs with gas, shot a puff of ether down it's throat, hooked up jumper cables and hit the starter. Starter spins but not the engine. Another bad bendix. Jumped on the kick starter and after just a few times it took off. Sounds just fine for 25,000 miles. It might be "OK". If so, other than some cosmetics and tires it could be on the road with another 8 hours work.! So I may have two that run...!

What's wrong with yours and why aren't you driving it around being cool and picking up chicks?

If it's carbs, send them over. I've done so many it's easy. Am going to have another gin and go to bed.

Thanks!

Wild Bill

Date: Mon, 19 May 1997 09:49:06 -0600
From: Bill Johnsen

It pops out of 1st and 2nd gear. Since last message

Engine was removed

Case split

Changed complete transmission, shift forks, tumblers and ratchet assy

with a spare set

Reassembled

Stripped the paint from the frame and repainted

Engine reinstalled in frame

I didn't run a compression test, hope the engine is "OK"

Wiring and cables are not yet reconnected

Was a real big job..

My manual is for a 73 and not a 74. You must remove the deep sump on the 74 to R&R the engine.

The special tool needed to pull the alternator flywheel is a 16 mm by 1.5 mm hardened bolt. They are hard to find the rear shock mount on a Toyota 4x4 pick up is the same and worked just fine.

Can't find a paint code for the purple metallic paint. Any suggestions?

Rear brake shoes are shot. There is someone somewhere on the net selling just shoes but I lost the address..

Thanks

Wild Bill

Date: Tue, 27 May 1997 08:34:50 -0600
From: Bill Johnsen

It runs and drives. What a chore...........................

This was the most difficult repair I have ever done on a motorcycle. Every bit of this bike was removed and rebuilt just to get it to go down the road and it's still not done. It's been 20 years since I've ridden this model and it did bring back some old memories.

Low end torque is great, transmission is geared high, clutch drags a bit making neutral hard to find at a stop,handles only "OK", sits high like most of the older bikes and overall is a bit clumsy. It's lots of fun though and if you nail it, has plenty of power.

Have since picked up a 1973 that's completely orginal and nice but not running. Motor isn't a 73 though. It seems to be a Yamaha replacement warranty motor because it has the appearance and goodies of a 74 with no ser # on it. It just never had a number stamped into it. The guy I bought it from says it ran fine but he is a 650 lover and just never got around to getting it on the road. It's real decent and came with - extra seat, new battery, spare guage set ( that I need) , extra pair of side covers. The bike other than the faded paint is quite nice. Maybe next month I'll fire it up and see what I have for my $300. investment. Do you know of any TX750 mechanical experts. I'm still having electric start problems. The bendix clearances are real crytical. There are three round balls that are part of the bendix and get all beat up and are expensive from Yamaha. When cleaning the garage yesterday I was about to pitch an old Honda 750 four starter bendix that I don't need and they are dime a dozen. I tore it aprt first and the balls are identical. Before buying expensive starter parts, get used balls of a dead Honda. Need paint and a windshield.

see you

Wild Bill

Date: Wed, 25 Jun 1997 09:59:36 -0600
From: Bill Johnsen

I was surprised to hear from you. I thought maybe you lost interest in the TX750. Your right, the gearing is a little tall and you need to slip the clutch or give it a bit of throttle to get it off the line. It's "OK" once you are used to it. Wiring isn't difficult but there isn't much I can do from here to help you. Once you get into it with a meter and a schematic you should have it all fixed in about an hour.

The starter is an inherent problem with the TX750. The drag of the motor was too much for the starter clutch and wore it out prematurely. You can tear it apart but it won't do any good until you replace two parts. You will also need a special tool to get it at. You can make one very easily and I'd be glad to explain how but I left my technical log book at home with the specs in it. The clutch has two parts that fail.!

1. The starter drive sprocket, the big one that is parts of the clutch. The center where the three clutch balls grab it wears down causing the clutch to slip, thus ruining the three round engagement balls. It wears only .002 to .003. This isn't much but the tolerances were really close to get this to work.

2. Three round shaped balls that fit in the outer housing that actually engage with the sprocket. I haven't ordered any from Yamaha because they are identical to the old Honda 750 (4). There is at least a million dead Honda 750 motors around where you can steal these and they usually don't cost over $10.00. The Honda was better designed and since it was a four there was less of a load on the starter clutch. Even the ones I have picked out of rusty crusty motors have seemed to be in excellent condition.

After these parts are replaced there is still a possibility of a little slippage if your battery isn't up to snuff. The starter must spin to speed to have the clutch hold.

My original 1974 that I replaced the transmission, clutch and starter clutch is in good running order and works fine since I replaced the battery. This one is a good daily driver now other than the paint. It's original but terribly faded. Fortunately my neighbor is a sign maker that has one of those $35,000 vinyl cutting machines and has made perfect original decals. The paint I had matched at the body shop supply place with their new computer scanner and now I am just awaiting the ambition to sandblast the parts and get it done. I'm a bit burnt out on paint because I just did my Moto Guzzi and I hate painting even though I'm good at it.

Since we last talked I have purchased and Original 1973 TX750 with a factory warranty replaced motor in it. Motor has no ser numbers and appears to be a 1974. Runs great, is all original, needs paint, tires and chain and sprockets. Paid $300 for it

Several weeks ago I also found another 1974 TX750 in rough shape. Bought it from a 75 year old Indian for $30. Cleaned the carbs, put in a battery and it seems to run just fine. Looks like hell but is very restorable.

Last week Friday, went back to Alfa Heaven and bought a spare locked up awful looking TX750 motor for $50.

So my inventory for TX750s is adequate. If you know of any lying about cheap, you should snatch them up. There are quite a few local cycle salvage yards and they all had at least one of these a month ago. Last week when I felt like getting a spare TX750 for parts, three that I knew of were gone. The yards all said that they have had no call for these for 15 years and now everyone wants one.

I also have two TX500s. Both with sick motors but otherwise very, very nice original shape. Do you know anything about these?

Good luck !

Wild Bill

Dear Mr. Cole, Was good to hear from you today. You are the only one that ever contacts me about the TX750s. I don't have an easy fix for starters. All I've done is measure new starter drive sprockets to determine what size they are suppose to be and calculated how much wear there is on the ones that no longer engage. The only way to repair these is to either buy a new sprocket and replace the three hardened engagement cylinders that contact this sprocket. New sprockets are still available from a dealer out East but the cylinders are not. Fortunately they are the same size as a Honda 750 except the Honda is a bit too long. Any valve grinding shop can shorten them. If sprockets are no longer available you could turn down the engagement area, hard chrome them oversize and then machine them to the original size. The 73 and 74 TX I drive have working starters that I repaired for less than $100. each. The 74 parts bike doesn't have a working starter but I have the new parts. Your starter also will not work and will kick out prematurely and cause starter damage if your battery is not in perfect working order. If it's down a bit, even a good starter will start to slip. It's the torque of the starter that keeps it from slipping. I will participate in assistance any way I can concerning the TX750. Am looking for the TX500 wizard. Is there one out there? Did Tom loan you a tank? What other bikes do you have?