check valve question ?

[Eddie]

high guys , im just wondering when you guys say the bike might smoke more because of a clogged check valve, are you talking about the valve at the bottom of the crank case or the one at the top of the jug? my left cylinder still smokes more than the other cylinders and I thought I had solved the problem back when I rebuilt the carbs, the left float needed adjustment, after I adjusted it seemed better but now its smoking more again, I have cleaned the check valves at the bottom and it didn't do anything unless maybe the left one is some how not working ? or stuck open ? if that's possible? also this is the cylinder that had the lowest compression not sure if its because of the rings possibly sticking? would that cause more smoke? the smoke does mostly go away when its warm, but sometimes it doesn't go away and its enough that you can see it pretty well,,,,,,just wondering if anybody has any ideas or maybe I should get a new check valve and see what happens? also the left muffler is noticeably more wet than the other mufflers, not sure if that's normal? radiator fluid level is fine and I always check it,,,,,

[tz375]

We are talking about the check valve in the oil supply lines. The oil drains into the crankcases when standing and makes a lot of smoke until it is burned off.

[Eddie]

Ohh right sorry , I know about those mine did leak a little but not much, I thought the sris check valves could also create this issue? Or is it just the check valves from the octopus that can make it smoke more?

[tz375]

A leaky SRIS valve could allow fuel or oil to pulse back and forth I guess. The real problem typically is the octopus check valves which allow oil to drain into the crankcases. A slow weep is still enough to make a lot of smoke on startup and would dissipate as the bike gets hot and burns it off.

[pearljam724]

I've had crank seals take a crap on 2 bikes in the past 2 years. One a GT 750 and the other an RZ 350. Both had the same exact smoking problem you speak of. Other than a leak down test and the snorkel on the 750 . The easiest for sure sign that a seal is leaking is checking the plugs. The spark plug that goes to that cylinder's crank seal will drastically be leaner than the others. No matter what fuel or air adjustments you make to the carburetors. It's very obvious as to what creates that. The plug is reading leaner because that cylinders crank seal is leaking. That is the case if you can't get the plugs to read the same at the same air/fuel mixtures settings. That is a fool proof sign. If that's not the case. The seals are fine.

[Eddie]

thanks pearljam, so since its the left cylinder the , the left plug should be lean correct? I will take her for a ride and then check, thanks for the info!!!!

[pearljam724]

thanks pearljam, so since its the left cylinder the , the left plug should be lean correct? I will take her for a ride and then check, thanks for the info!!!!

You're welcome bud. Yes, that's correct. Before I rebuilt my motor. The left cylinder by coincidence was the seal that blew on mine. Mine smoked very little out the left cylinder pipe. A ride before it let go. I found a fraction of a piece of crank seal wedged in my left cylinder spark plug electrode. The ride after that, crank oil was puking out of my snorkel and the left cylinder spark plug was very lean compared to the others. I knew it was time to rebuild. If the carbs are clean and all of them have the same size jets. That plug may not read extremely lean. But, much leaner than the others. If the carbs are in good order. All air, fuel settings are the same. And the carbs intake butterflies are synchronized to one another accurately. If you have the original seals and likely you do. I would start planning on have the seals replaced. It's not that bad of an ordeal if you talk to the right person. Start saving money for that purpose. A reasonable charge is about 800 to 1500 bucks. Someone wants more. Walk out the door. Don't let someone get away with trying to charge you hourly.

[tz375]

Eddie,

Is the left plug looking lean or is it all oily?

[Eddie]

The left plug looks slightly lean compared to the others, after I took it for a 10 mile ride I checked and it looked better but still a tad lean compared to the other plugs, I tried posting pics but it said board quota had been reached? ill try again... well it wont let me post the pics , board attachment quota has been reached? so the left plug is slightly lean...

[pearljam724]

You have to set up an account on photobucket. Takes 5 minutes. Once you add pictures to your bucket. Just copy the link for that specific picture. Then paste it on your message here. It allows the picture to appear for at least a couple days. When you add the pictures. Show a picture of all 3 plugs side by side.

[Eddie]

thanks pearljam,,, not sure if ill have time right now but I will try later, im computer stupid so 5 minutes might take me 5 hours , the left plug looks lean on one side and normal on the other, that's why I was trying to post the pics,, I really hope the seal is ok but if not I hope it lasts for a while, not in the mood to rebuild a motor right now, got to many other things going on,,, I know I will have to send the crank to bill bune ,, just wondering though, if I do have to rebuild , hopefully much later, where do you guys get the crank seals? and I know they changed them during production not sure what year, but mine is a 74 model but I think its an early 74, it doesn't have the O-rings or rubber seals on the head bolts, and the head has never been off, I had checked the numbers a long time ago and mine was an early 74 that didn't get that change....so the head will probably be a bi@#ch to get off, also just wondering if the seal is bad and sucking air wouldn't it affect the idle????

[pearljam724]

thanks pearljam,,, not sure if ill have time right now but I will try later, im computer stupid so 5 minutes might take me 5 hours , the left plug looks lean on one side and normal on the other, that's why I was trying to post the pics,, I really hope the seal is ok but if not I hope it lasts for a while, not in the mood to rebuild a motor right now, got to many other things going on,,, I know I will have to send the crank to bill bune ,, just wondering though, if I do have to rebuild , hopefully much later, where do you guys get the crank seals? and I know they changed them during production not sure what year, but mine is a 74 model but I think its an early 74, it doesn't have the O-rings or rubber seals on the head bolts, and the head has never been off, I had checked the numbers a long time ago and mine was an early 74 that didn't get that change....so the head will probably be a bi@#ch to get off, also just wondering if the seal is bad and sucking air wouldn't it affect the idle????

Idle isn't effected that I ever noticed. I don't think you'll have a problem removing the head. Mine had never been off and came off with no problem at all. Just be careful with smaller bolts. If you do remove the head. Just start the bike and allow the motor to warm up first and shut it off. That will help a great deal. Once the crank is sent out to Bill Bune he can take care of all parts needed for the crank including the seals. But, depending if he suggests new bearings, rod cones, etc when he looks at it. The cost can vary a little. Mine cost $250 plus shipping. Which is very reasonable. The cost you will see is the price you pay someone to remove it and install it. If you don't do it yourself. If you do it yourself. That's the only cost you would be looking at. Other than replacing cylinder head and base gasket. Start talking to people around you. It will take a long time to find the right person. That point alone is worth getting the ball rolling for when that time comes. I gotta go. Richard, will be glad to help you with your pics.

[tz375]

So it sounds like potentially a leaky left seal plus leaking check valve allowing oil to drain down. Crank is easy to fix as PJ mentioned. It take time to remove strip clean and rebuild a motor. Most time is in cleaning and inspection and repairing damaged threads and surfaces and scraping all the gaskets off.

You can do all of that yourself should you be so inclined. Getting someone else is just paying for labor and if time is more important than cash, that's always an option. If your motor has never been opened up before, the work is usually a lot less than if it has been rebuilt! You do not want to hear some of the horror stories I have seen recently on rebuilt motor.

I have one on which the cases had to be completely stripped and will require extensive welding and machining to repair all the gouges from someone prying the barrels off. And the bottom half of the case was a 72-73 with a 77 top half.

Unmolested is always nicer.

What part of the world are you in?

[Eddie]

I will be doing the work myself, I am located in West Texas , I guess ill just keep riding it until it dies? I still havnt set up the photo bucket just got home, started watching the packers vs sea hawks game,,,,

[pearljam724]

I will be doing the work myself, I am located in West Texas , I guess ill just keep riding it until it dies? I still havnt set up the photo bucket just got home, started watching the packers vs sea hawks game,,,,

If it were me. I'd ride it throughout the summer and regardless of the seals holding up that long or not. I would remove the motor and start tearing it down over the winter. You have a lot of good people here that can walk you through the whole process. If you start by late fall. There is no reason why you wouldn't have the bike up and running come that following spring. If you put an hour or 2 into it a couple days a week. Don't be intimidated. You'll realize just how easy things are once you get involved and learn some tricks or pointers to help you along. If time or confidence is a concern. Pay someone else to do it. The most difficult part will be the realization of how freaking heavy the 750 motor is to move around by yourself. But, that isn't a big deal either if you take a good approach. As of now I would remove the head bolts only. Which takes 30 minutes. Spray some PB Blaster followed by a silicone lubricant down inside the cylinder bolt holes. That may give you the luxury of pulling off the cylinders without a problem when the time comes. You have to torque the head bolts in proper sequence and the proper torque settings. Very easy.