Common issues with 750 smoking more out of 1 exhaust side ?

[pearljam724]

I just bought a restoration project 750. The bike is in fair cosmetic and running condition, but needs quite a bit of love and money put into it. One exhaust side smokes particularly more than the other. But, runs fine. Should I be alarmed ? I believe that it's not right for it to smoke considerably more on one exhaust side. My guess is piston rings ? I rate myself to be pretty inclined in reference to motorcycle repairs. However, with the exception of valve adjustment top ends. I have no experience with other internal motor work. But, in the last several years I've learned multiple things that I was once intimidated to attempt to fix. What common occurrences can I look for to remedy this symptom ? And how difficult would it be rated to dis and reassemble this motor with a guy of my experience ? I've been wrenching on bikes for nearly ten years, but like I said. Very little internal motor experience. What would you guys suggest and how difficult is it to rebuild one of these motors ? In reference to me doing it, paying a shop and how available are new internal motor parts ? I know motor gaskets can easily be found. But, what about possible piston work ? I also know the best thing to do is check for compression. How do I go about it and where would I go from there ? A lot of questions, I know. Ha Ha

[tz375]

If it's from the center or right side, it is most likely to be a crank seal allowing transmission oil in. It could also be an oil feed check valve that is weeping (cracked open).

To clear that, remove the oil pump and starter cover and carbs to get to the 6 banjo bolts. Flush out all six lines with alcohol but do NOT use compressed air because it will probably ruin the tiny ball valve in there.

Another quick check is to drain the oil tank and refill it with oil of a different color and let the bike stand for a week and see if any of the oil lines have changed to the new oil color while it was not running. In fact I am about to do that on my bike this evening to see if I have a leaky valve.

[pearljam724]

If it's from the center or right side, it is most likely to be a crank seal allowing transmission oil in. It could also be an oil feed check valve that is weeping (cracked open).

To clear that, remove the oil pump and starter cover and carbs to get to the 6 banjo bolts. Flush out all six lines with alcohol but do NOT use compressed air because it will probably ruin the tiny ball valve in there.

Another quick check is to drain the oil tank and refill it with oil of a different color and let the bike stand for a week and see if any of the oil lines have changed to the new oil color while it was not running. In fact I am about to do that on my bike this evening to see if I have a leaky valve.

Thank you, a ton. In the first and third paragraph. Are you referring to the same valve ? " The oil-feed check valve ? If it is cracked open as you say. Can I close it or do I have to replace it ? And how detailed is it to change the crank seal if I want to do that for good measures ? The six banjos, I'm assuming connected to the oil feed lines ? If so, why would I want to flush those if they are suppose to have oil in them ? Thank you, very much.

[Coyote]

You flush the 6 lines with alcohol to free up sticky parts (valves). Those 6 little valves at the banjo end of the lines are check valves. They are supposed to close when the motor is not running. This prevents the oil in the tank from filling the crankcase due to simple gravity. You can't turn them on and off manually.
You have to remove the carbs to get at the 6 banjo bolts. Remove the bolts, then remove the oil pump. Under the pump is a plastic manifold. You flush the lines from that end. When you are finished, you refill the lines with 2 stroke oil before reassembly. A simple way the see if the valves are working is to fill the lines with oil and hang the manifold on a nail. Leave it for 24 hours. The lines should still be full and no oil on the floor.
The valves are not replaceable. The parts are no longer available so you have to work with what you have. As stated above, do not use compressed air. It over stresses the spring in the valve and it will never seal again. For flushing, I use a cheap pump type oil can and plain old rubbing alcohol.

[pearljam724]

You flush the 6 lines with alcohol to free up sticky parts (valves). Those 6 little valves at the banjo end of the lines are check valves. They are supposed to close when the motor is not running. This prevents the oil in the tank from filling the crankcase due to simple gravity. You can't turn them on and off manually.
You have to remove the carbs to get at the 6 banjo bolts. Remove the bolts, then remove the oil pump. Under the pump is a plastic manifold. You flush the lines from that end. When you are finished, you refill the lines with 2 stroke oil before reassembly. A simple way the see if the valves are working is to fill the lines with oil and hang the manifold on a nail. Leave it for 24 hours. The lines should still be full and no oil on the floor.
The valves are not replaceable. The parts are no longer available so you have to work with what you have. As stated above, do not use compressed air. It over stresses the spring in the valve and it will never seal again. For flushing, I use a cheap pump type oil can and plain old rubbing alcohol.

Gotcha. The same concept with some automatic spring loaded timing chain tensioners. Some people are too quick to buy a new one. Because they are told that over time the spring becomes too weak. That is true, however. More often than the spring becoming weak. If you simply remove it and spray it with brake cleaner to remove the scorn oil residues the tensioner once again works like it should. Without the sound of the timing chain or belt slapping around inside the motor. Thank you, for the great tip. I'm hoping that will resolve my over abundant smoking issue. If not, how hard is it to replace the crank seal ?

[tz375]

The glib answer is that it's easy.

Remove motor
Strip motor
Remove crank and ship it to Bill Bune with a set of seals
Assembly is the reverse of the strip procedure

That's more or less what's involved. The crank has to be pressed apart to replace the seals. Bill Bune and his guys do lots of cranks for all manner of bikes PWCs and snowmobiles, so they know cranks. That doesn't mean that they know all the intimate details of every crank ever made but they know what they need to know and where to find answers.

I have had them do several GT750 and Honda twin cranks and so far no complaints.

[pearljam724]

The glib answer is that it's easy.

Remove motor
Strip motor
Remove crank and ship it to Bill Bune with a set of seals
Assembly is the reverse of the strip procedure

That's more or less what's involved. The crank has to be pressed apart to replace the seals. Bill Bune and his guys do lots of cranks for all manner of bikes PWCs and snowmobiles, so they know cranks. That doesn't mean that they know all the intimate details of every crank ever made but they know what they need to know and where to find answers.

I have had them do several GT750 and Honda twin cranks and so far no complaints.

Thanks, Tz. I gave his shop a call. Estimate with parts and labor was $350. Ouch

[tz375]

..................A simple way the see if the valves are working is to fill the lines with oil and hang the manifold on a nail. Leave it for 24 hours. The lines should still be full and no oil on the floor............

Chris, Great idea.
I just tried that on my octopus for the next bike and sure as fate, two of the lines just emptied out as I watched it.

[ConnerVT]

Estimate with parts and labor was $350. Ouch

Yeah, but think of the money you save not replacing valves, valve seals, camshaft chains, tensioners...

The crankshaft is really the only complex part of the motor (sans transmission). Everything else is a static cast aluminum piece. Once rebuilt, it is set for a long time.

[pearljam724]

Estimate with parts and labor was $350. Ouch

Yeah, but think of the money you save not replacing valves, valve seals, camshaft chains, tensioners...

The crankshaft is really the only complex part of the motor (sans transmission). Everything else is a static cast aluminum piece. Once rebuilt, it is set for a long time.

You're right. But, I'm gonna pass on Bill Bune. I understand shops are going to make money on parts. But, I priced the seals. There are five totaling $80 on the few sites I checked. He is making $70 on five gaskets alone from the quote he gave me. Said 200 for labor, which is fair. I understand you're gonna make a fraction on parts. But, $70 ? That's nearly a %100 profit on parts. For that reason, I won't do business there.

[pearljam724]

..................A simple way the see if the valves are working is to fill the lines with oil and hang the manifold on a nail. Leave it for 24 hours. The lines should still be full and no oil on the floor............

Chris, Great idea.
I just tried that on my octopus for the next bike and sure as fate, two of the lines just emptied out as I watched it.

What happens when you can get the valves to close by cleaning them ? Throw the bike in a trash heap, because they no longer manufacturer the part ?

[tz375]

I'd guess you keep an eye open on ebay or get replacement valves and splice them in to the lines.

On my spare, after a couple of hours two lines are completely drained and two others are seeping very slowly.

I just pulled the right SRIS valve - well it's blocked off with a cap screw, so that's what I removed and out came 250ml of fresh clean oil. 250cc through the transfer ports into the 31cc combustion chamber could have proven fatal for the rods. Now to clean out the spare and swap them over if all goes well.

And I thought I had checked the oil supply meticulously when I was rebuilding the motor. Maybe there were specs of dirt in the oil tank that I missed that are now cracking at least one line open. Here we go again.......

[oldjapanesebikes]

I'd guess you keep an eye open on ebay or get replacement valves and splice them in to the lines.

Splicing for the moment seems the way to go if you can't locate a good replacement. If you search back through this board you will find Coyote's post on how he did it. I posted over on the Kettle Clinick in the UK about my own attempts. This is the link:

http://www.kettleclinick.com/viewtopic. ... =20#p15839" onclick="window.open(this.href);return false;

[tz375]

Thanks Ian, Great link and thanks to Coyote Chris for the splice ideas.

Perljam,
Bill Bune's pricing is $250 for the crank strip, clean, inspect and rebuild. He's quoted an off the top of the head $100 for seals and if he has to search for part numbers and order them, $20 margin is less that normal on parts. His prices are fair. IMHO.

[RING_DING]

You could always fit a 3-1 and you'll never have to worry about one side smoking more than the other