Phase 1 complete and looking to phase 2

[Slowshed]

Great forum!

I started a project 12 years ago and finally finished phase 1.

It started as a 1979 XS650SF that was donated by a friend.

It is a hybrid between the XS650 and a 1986/7 YZ490. The frame and carburetors are about all that is left out of the original bike at this point. Front forks, triple tree, swing arm, wheels, rear shock and most of the linkage are YZ490. The rear section and tail section are from a 1974 Kawasaki F11, tank is a late seventies YZ80, motor is an early kick start only motor.

I set this unfinished project bike aside for years and eventually sold it to a buddy. It sat there for 4 or 5 years and I bought it back last year once I had renewed enthusiasm. I got it mostly finished in early summer, but had a lot of issues with the Pamco ignition that I had bought years ago and then more issues with the XS Charge ignition this summer. It got parked again until 2 weeks ago when I replaced the capacitor with a Li Ion battery. Since then it’s been great.

Working out ridability issues now, leaking rear shock, improving the front brake, rejetting the pilots, etc.

Been running well and even does pretty well on the trails.

Next phase is getting it reliable and finishing the original gas tank to allow more that 40 miles of range. I already have a second seat pan made and the steering stops are set to clear the original tank.

Today another friend donated another kick start only motor.

The current motor runs well, but must have been in an accident. There are broken fins on the head and cylinder. Also had a bent shift shaft that I had to replace.

So the extra motor is going to get an upgrade. I’ll do a big bore (but I’m not sure how far) and I’m considering the Hugh’s rephrase.

I’ll be searching this forum for feedback on the big bore, porting and if the rephrase is worth the money. Reliability is top priority. Motor already does fine, but is a bit flat on the power delivery.

I’ll take any advice this group may have.

 

[Signal]

I like your bike, to answer your questions

Reliability no problem with 750 big bore, get an 8 plate clutch from GGGary job done.
Not convinced rephase is needed, adds extra expense with cam, and ignition system.
For the record all my XS twins are rephased, probably would not head down that route again.

All performance cams need better valve springs (more expense).
Stock oil pump (in good order) is fine for 750.
Before you spend money on parts ask on here as someone will have tried it and be able to tell you if its good or not.

My opinion best bang for buck:
750 big bore
Quality port job on head (this is the key part after cc's)
Ignition, just not points or cheap stuff from ebay, stock TCI is fine. These bikes dont need super fancy ignitions 35 degrees total advance is about all you need.

 

[Slowshed]

One of the issues I needed to address is a rear shock that is leaking badly. I rebuilt the forks with new bushings and seals, but the rear shock shaft (both from the YZ125 and YZ490 doner bikes) was pitted. I was putting off trying to fix them, but now that it’s on the road and the trails I can’t put it off any more.

A few days ago I tried zinc playing the shaft of the spare shock to fill in the pitting. It worked out well so far.

This is the shaft after zinc plating. You can see where the pitting was. The pitting at the bottom is not in the travel area.

This is after hitting with a buffing wheel. You can still see it, but you cannot feel it.

Shock reassembled. This is a bit of a test so I just cleaned the existing seal head and piston, used some 5 weight fork oil.

Recharged with N2 and swapped out on the bike.

 

[Kevin Werner]

I will add my 2 cents. Nice build. I have a '77 750 BBK with I believe to be a stock cam. I can see that motor in your bike if you are doing trail riding. Good wideband power delivery. I think mine is a 9.5:1 CR. I have BS38s on it. My other XS650 has VM 34s and these would by a real upgrade because I remember dirt riding 40 years ago and nuanced throttle can be everything in enjoying a bike on the trails. I am no longer a WFO rider bit when I was there were still many time that dialing on a little throttle rather than WFO worked best. VMs do that a little better than BS carbs do. I don't know just how fast you are but you might be really happy with 750 BBK and VMs. As you seem capable and willing, you might look into lowering the rotating mass (lighter rotor or shaved crank wheels) for better throttle response.
Cheers

 

[Slowshed]

Please tell us more!

I like your bike, to answer your questions

Reliability no problem with 750 big bore, get an 8 plate clutch from GGGary job done.
Not convinced rephase is needed, adds extra expense with cam, and ignition system.
For the record all my XS twins are rephased, probably would not head down that route again.

All performance cams need better valve springs (more expense).
Stock oil pump (in good order) is fine for 750.
Before you spend money on parts ask on here as someone will have tried it and be able to tell you if its good or not.

My opinion best bang for buck:
750 big bore
Quality port job on head (this is the key part after cc's)
Ignition, just not points or cheap stuff from ebay, stock TCI is fine. These bikes dont need super fancy ignitions 35 degrees total advance is about all you need.

I like your bike, to answer your questions

Reliability no problem with 750 big bore, get an 8 plate clutch from GGGary job done.
Not convinced rephase is needed, adds extra expense with cam, and ignition system.
For the record all my XS twins are rephased, probably would not head down that route again.

All performance cams need better valve springs (more expense).
Stock oil pump (in good order) is fine for 750.
Before you spend money on parts ask on here as someone will have tried it and be able to tell you if its good or not.

My opinion best bang for buck:
750 big bore
Quality port job on head (this is the key part after cc's)
Ignition, just not points or cheap stuff from ebay, stock TCI is fine. These bikes dont need super fancy ignitions 35 degrees total advance is about all youneed.

Thank Signal!

I’m running the XS Charge points eliminator with a 3ohm Dynatek dual output coil. Stock mechanical advance and timing.

I’m also running the PMA setup from Mike’s.

I was looking into the rephrase. I was wondering why the 277 instead of a 270 or 285. After some research I learned that the crank is splined and that’s the reason for doing a 277 rephrase. That part we could do on our own, but I’m not sure I want to tackle rephasing the camshaft. I haven’t figured out the ignition setup.

I appreciate the advice on the rephrase. If you’re running them I sure you run enough of the stock motors.

This bike is going to get used as a dual sport so low to mid-range power is best. I don’t want to go too high on compression. It is a kick-start only motor and the kick lever is pretty high with all that ground clearance.

Thanks again and I’ll keep researching.

 

[Slowshed]

I will add my 2 cents. Nice build. I have a '77 750 BBK with I believe to be a stock cam. I can see that motor in your bike if you are doing trail riding. Good wideband power delivery. I think mine is a 9.5:1 CR. I have BS38s on it. My other XS650 has VM 34s and these would by a real upgrade because I remember dirt riding 40 years ago and nuanced throttle can be everything in enjoying a bike on the trails. I am no longer a WFO rider bit when I was there were still many time that dialing on a little throttle rather than WFO worked best. VMs do that a little better than BS carbs do. I don't know just how fast you are but you might be really happy with 750 BBK and VMs. As you seem capable and willing, you might look into lowering the rotating mass (lighter rotor or shaved crank wheels) for better throttle response.
Cheers

Great points!

I am a moderate C rider off-road and I don’t have illusions that this will ever be a motocross bike. Just a fun bike to ride that isn’t run-to-the-mill.

So far the 750 kit is looking like a go.

 

[Raymond]

I see you're considering a re-phase and there are loads of people running re-phased engines. However, reading about the subject I'm not convinced of the value making that change, the impression I've gained is that you move the vibes to a higher rev range and also move the power to a higher rev range.

I like the feel of the standard motor and the low down shove it gives.

I like the idea of a big bore for more of that shove.

 

[Slowshed]

I hadn’t read that the rephrase pushes the power higher in the rpm range. If that’s true, I definitely don’t want that. This bike needs power in the low to mid range.

The motor that is in the bike I believe is an XS1B, but I’m not certain. Serial number is 650-100xxxx, but the motor that I’m going to build and was just donated to the project is an early version, probably an XS1. Serial number is 650-003289.

The motor came with a second or third hand story that there was a noise somewhere. from what I’ve read it likely has rods with needle bearings on the small end that are prone to failure. So I’m planning on splitting the cases and the crank to use 447 rods with bushings.

My buddies and I could rephase the crank. We’ve done enough 2-stroke single cylinder cranks. I don’t know if anyone has done a twin 4-stroke crank but I’m sure we can figure it out since it’s splined.

I’m in a dream situation for old motorcycle mechanics. I rent space in my buddy’s shop in an industrial park, but there are 4 more shops in the same row that are all retired gear heads and one of them is still a semi-retired fab shop. I have keys to all the shops, equipment, materials and talent of the other guys.

But as far as the rephase goes, it’s sounding like I should rebuild the crank with new rods and keep the 360 configuration.

 

[Raymond]

. . . I’m in a dream situation for old motorcycle mechanics . . .

Sounds like it!

On the re-phase, opinions vary but I think it is more or less a conversion that suits racing engines.

 

[Ratranger]

Looks like the engine in the bike has a later head on it. The early XS1 and XS1B heads had all triangular valve covers. The square cover on the left exhaust side started when Estart was added for a decomp setup.

 

[Slowshed]

Wow, the amount of usable information on this forum is outstanding! I’m glad it was a long weekend. Lots of research and getting good results. Thank you!

Between people’s direct replies and the search function here I have a lot more insight to what I want this motor to do and how to get there. I’m going to throw up a first draft of a plan so I remember it and see where the holes are that I need to think about.

I have 2 issues to deal with as far as the bike goes and what I’ve already done with it.

First, the XS1B motor does mount slightly differently than the 1979 motor that was originally in it. Unfortunately that motor is long gone … it’s looking like I could use its parts now. The XS1B motor is tilted slightly forward when mounted in the frame. This became apparent when I had make new front motor mounts and the brackets I had made to hold the air box (built around the 1979 motor) were way too long with the XS1B installed. That is driving me to stay with the XS1 motor.

The second issue is the final drive gearing. Since I’m running the YZ490 wheel and hub I’m limited to a 41 tooth rear sprocket (40 if we machine the hub where the chain rides on the sprocket). I’ve already got an 18 on the front so there is no more room there. It’s okay now with the knobby tires, but I’ll lose some top end when I go to regular dual sport tires, which I need to do for safety on the road. The 5th gear overdrive is sounding good, but that requires the later transmission.

It also looks like installing a 750 bbk is much simpler with a 447 motor. So this morning’s plan is:

Use the XS1 motor cases
Get a 1978 or later 447 doner motor for crank, rods, pistons and transmission.
Stay with the 360 configuration- no rephase
750 BBK
Shellie cam? Not sure of the power range?
New valve springs
Port / Polish head
Maybe 34mm carbs?

Since I want low to mid range power, using the whole 447 crank seems like the best option. It solves my needle bearing small end issue, gives me shorter conrods (which I just learned are better for low rpm vacuum and torque) and eliminates the camshaft drive gear difference issue.

Using the 1978 or later transmission looks like it may be necessary for running the 5th gear OD.

Sorry for the long post. Writing this out helps me think these things out. Please let me know if some of the gurus here see any holes or opportunities I missed!

 

[Slowshed]

Looks like the engine in the bike has a later head on it. The early XS1 and XS1B heads had all triangular valve covers. The square cover on the left exhaust side started when Estart was added for a decomp setup.

Good eye. I did not know that. I’ll check the XS1 motor head when I go to the shop later today. TY!

 

[Raymond]

The second issue is the final drive gearing. Since I’m running the YZ490 wheel and hub I’m limited to a 41 tooth rear sprocket (40 if we machine the hub where the chain rides on the sprocket). I’ve already got an 18 on the front so there is no more room there. It’s okay now with the knobby tires, but I’ll lose some top end when I go to regular dual sport tires, which I need to do for safety on the road. The 5th gear overdrive is sounding good, but that requires the later transmission.

Yup, I'd think that 18:41 final would be an issue right enough. Add a big bore and you'd be calling the bike 'Down, Boy!'

@Adamc has a lovely tracker and IIRC that came to him with very short gearing?

 

[Slowshed]

I got excited looking at the OEM diagrams. It appears that the 1973 TX750 and the 1970 XS1 share a lot of the same transmission components. Unfortunately 5 th gear pinion and wheel are identical. That doesn’t help me gear it up.

That would normally be a hassle to source, but one of my other projects happens to be a 1973 TX750 ad I have a spare transmission sitting there.

That was it last fall. Since then the motor has been rebuilt, got a title through Ohio (no small feat) and it is running.

It’s currently on the lift next to the XS waiting to get stripped down to the frame.

 

[46th Georgia]

I hadn’t read that the rephrase pushes the power higher in the rpm range. If that’s true, I definitely don’t want that. This bike needs power in the low to mid range.

The motor that is in the bike I believe is an XS1B, but I’m not certain. Serial number is 650-100xxxx, but the motor that I’m going to build and was just donated to the project is an early version, probably an XS1. Serial number is 650-003289.

The motor came with a second or third hand story that there was a noise somewhere. from what I’ve read it likely has rods with needle bearings on the small end that are prone to failure. So I’m planning on splitting the cases and the crank to use 447 rods with bushings.

My buddies and I could rephase the crank. We’ve done enough 2-stroke single cylinder cranks. I don’t know if anyone has done a twin 4-stroke crank but I’m sure we can figure it out since it’s splined.

I’m in a dream situation for old motorcycle mechanics. I rent space in my buddy’s shop in an industrial park, but there are 4 more shops in the same row that are all retired gear heads and one of them is still a semi-retired fab shop. I have keys to all the shops, equipment, materials and talent of the other guys.

But as far as the rephase goes, it’s sounding like I should rebuild the crank with new rods and keep the 360 configuration.

The late great @grizld1 had the opinion that all the re-phasing did was move the engine's vibrations to a different RPM range and that it didn't produce any more H.P. or torque. They (270's) do sound better though, IMHO.

 

[John Regular]

The late great @grizld1 had the opinion that all the re-phasing did was move the engine's vibrations to a different RPM range and that it didn't produce any more H.P. or torque. They (270's) do sound better though, IMHO.

I started writing down some of his quotes

 

[46th Georgia]

I started writing down some of his quotes

He P.M.'d me about it as he didn't want to start a feces fight with other forum members. I'll try to dig up the details as to his opinion on a good "hot rod" engine but basically, 700cc JE pistons, Shell #1 cam, head porting. Others here have ridden his bike and can chime in on it's performance.

 

[Slowshed]

He P.M.'d me about it as he didn't want to start a feces fight with other forum members. I'll try to dig up the details as to his opinion on a good "hot rod" engine but basically, 700cc JE pistons, Shell #1 cam, head porting. Others here have ridden his bike and can chime in on it's performance.

Do you know where the power was with his setup? Mid or top?

I’m not sure what the cam profile is.

 

[46th Georgia]

Do you know where the power was with his setup? Mid or top?

I’m not sure what the cam profile is.

Do you know where the power was with his setup? Mid or top?

I’m not sure what the cam profile is.

I believe more in the middle. Check with @XRZ100, I believe he built a similar engine.

 

[46th Georgia]

Do you know where the power was with his setup? Mid or top?

I’m not sure what the cam profile is.

I believe in the middle. Check with XRZ1100, I believe he did a similar build.