where to begin... looking for advice - RZ350

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Backwoods
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where to begin... looking for advice - RZ350

#1 Post by Backwoods » Thu Jun 22, 2017 3:51 am

I'm pretty new to all this so please forgive my ignorance. So the throttle cable snapped on my '84 RZ, It ran reasonably well prior to broken cable, but certainly not %100. Everything is stock and its the original '84 engine with 30K km. Last comp test found both sides 125 psi, put 1200km on it. I bought a replacement cable from Diablo, installed it, synced carbs, setup oil pump, now left cylinder doesn't seem to burn, exhaust is cool compared to right side with significantly less pressure and no 'pop'. Both cylinders are pretty rich, right side dried up after running for a bit, I had to pour fuel out of the left expansion chamber. I switched plug wires and installed new plugs and same condition occurred on left cylinder. There is fuel in the vacuum line off the petcock. I did a comp test :smt009
95psi right side 90psi left side. When the pipes were off I checked the power valve movement and the left side moves smoothly and opens fully the right side moves after the left and not as much in comparison. Both pistons show signs of blow by. How to procede?

I'm hoping to do a leak down test if I can finagle a kit together. Assuming the seals are good should I just rebuild the top end and carbs? I read here that sometimes the choke won't seal which can cause a rich condition on the left side, I suppose that may need replacing as well. Advice and opinions would be much appreciated.

Josh

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JonW
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Re: where to begin... looking for advice - RZ350

#2 Post by JonW » Thu Jun 22, 2017 4:55 am

sounds like you need to tap the left carb to get the fuel to flow... but if the pipe is full of fuel you may well need to look closer at the spark, tho with new plugs and swapped wires Im not thinking its that.

...also sounds like the PVs have worn in the center joint.

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Re: where to begin... looking for advice - RZ350

#3 Post by evan_calgary » Thu Jun 22, 2017 4:21 pm

You have a got a lot going on there! Best to start with one thing at a time and work your way through it. Personally would sort out the fuel leak and the tap leak prior to the rebuild. You could cause issues that result in yet another rebuild otherwise.

How well did you clean out the left cylinder after the first time this happened? If the thing is full of fuel it will just re-foul plugs.

If you are pouring fuel out of the left cylinder all the time, this could be a leaky float, very poor compression (no), or other carb fuel related issue. It sounds like the coil is firing since you switched them. Is there raw fuel in the reeds? I would guess this is likely.

Could this also be part of the issue with the fuel tap? More of a question to the forum.

The PVs I have seen very very rarely moved at the same time and the same amount. To check if Jon is correct about wear in the center, there are 2 very small allens between the cylinders. easy to take apart and easy to replace part.

Regardless I would address those things first.

Then, may only need new rings and a hone once the top end is apart.

Compression check on bottom end is always a good idea and an often forgotten one. Tell if the PVs are also leaking.

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Re: where to begin... looking for advice - RZ350

#4 Post by hondaror » Thu Jun 22, 2017 10:20 pm

Seems like you've done something wrong. Ran ok before.
Did you pull the carbs to change the cables?
How did you sync carbs?
The fact that the compression dropped just because you changed the cable sends red flags.
It does sound like the float is stuck open. Are the slides in the right carbs?
Mechanical sync does not cut it and problems arise when the carb sync is out of whack. You need a vacuum sync with a unisyn.
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Backwoods
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Re: where to begin... looking for advice - RZ350

#5 Post by Backwoods » Fri Jun 23, 2017 2:53 am

Thanks for all the replies. I did not pull the carbs when I replaced the cable they did get twisted in the intake boot to fit the slides back in tho. I removed each slide separately when I hooked up each cable so they couldn't have been switched. I synced the carbs using the popsicle stick method but with exacto blades. I haven't really had time to work on it much since. Tomorrow I guess I'll pull the carbs and check the floats and reeds. I also have a pair of vacuum gauges so I can do a measured sync. How can I tell if I can get away with just a ring replacement? If I can get the cylinder firing by sorting out the fuel issue just check if there I is little to no scoring on the cylinder walls I could just hone and replace rings?

Josh

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Re: where to begin... looking for advice - RZ350

#6 Post by JonW » Fri Jun 23, 2017 2:59 am

you can only hone and ring so much, if its done 30k on the first bore then im betting you need a rebore.
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Re: where to begin... looking for advice - RZ350

#7 Post by whyzee79 » Fri Jun 23, 2017 1:03 pm

You need to check it with a bore gauge to see if it can get away with a re ring or a re bore. 30k and I agree with JonW. Re bore would be the safe bet.

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Re: where to begin... looking for advice - RZ350

#8 Post by Backwoods » Sat Jun 24, 2017 1:53 am

Well apparently my memory is getting fuzzy. That and bubbly late night wrenchfests make for mistakes. Rory called it. I apparently pulled both slides and did a switcheroo. It was a happy accident tho because I probably wouldn't have done a comp test, or looked at the PVs until something far more serious occurred. So I'm ahead of the game a bit. It is running way better than it ever has for a long while. I guess my carbs were setup poorly before. I pulled them, cleaned them and put the correct slide in the correct carb. Amazing what that will do. I haven't done another comp test yet, no real reason it would change anyway as far as I can tell.

I hope to do a leak down this weekend. I'll also be constantly monitoring plugs and compression for a bit until I can get together the cake to buy the top end parts and machining as I sounds like it will need it. It's far too nice of weather in BC right meow to open things up.

If anyone is interested the diablo throttle cable (don't recall the manufacturer) is pretty good so far except the carb cables and throttle end could be a little longer and the oil pump cable could be a little shorter. In my setup to get everything where it should be the adjusters are close to their respective limits. Carb and throttle near full extension and oil pump near full retraction if that makes sense, but it works and there is still a slight amount of room to play.

Thanks again for the help. I'll keep things updated.

Josh

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Re: where to begin... looking for advice - RZ350

#9 Post by evan_calgary » Mon Jun 26, 2017 11:26 am

Should not impact your compression test unless not done correctly in first place...

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Re: where to begin... looking for advice - RZ350

#10 Post by Backwoods » Wed Jul 05, 2017 5:19 am

Well it looks like I'll be rebuilding the engine sooner rather than later. I was out on a ride and I lost power. Tried to start it again and it ran on one cylinder and puffed a lot of air. After getting it home I pulled the plugs and they kind of looked ok, but the right side was very dry. I did a comp test and found 90psi on the left as expected and 0 psi on the right. Uh oh.

After pulling the exhaust all I saw was rings and a gaping hole where part of the right side piston should have been.
IMG_1569.JPG
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So I am wondering whether running the right with the backwards slide (I put the slides in the wrong carbs) contributed to this, or that when I pulled the oil pump cover off to disconnect things the pump control mechanism was stuck in the full throttle position. Maybe one of the better versed members has an idea. I touched the ring that the cable wraps around to remove the cable and it sprung back to idle position.

And to think I just missed out on a mixed lot of rz parts on eBay of bottom end seals and bearings and other goodies for a great price.

An additional question I have is what are folks opinions on the Wiseco piston kits and gaskets? I understand that OEM head gaskets are recommended, but what about the rest? More to come as I tear it down.

Thanks ,

Josh

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Re: where to begin... looking for advice - RZ350

#11 Post by silverstrom » Wed Jul 05, 2017 4:35 pm

That looks like the left cylinder, not the right.

Did your temperature gauge indicate that the motor was very hot? Typically it would with that level of carnage.

How is your coolant level? Still good?

Here is the by-the-book diagnosis of piston damage on the exhaust side

Air leak at the magneto side crankshaft seal, too lean carb jetting, too far advanced ignition timing or faulty igniter box, too hot of a spark plug range, too high of a compression ratio, too low octane fuel. You may be dealing with more than one issue. If the bike is new to you it is likely the you inherited someone else's problems.

A compression test is useful for diagnosing ring condition, but unfortunately it doesn't tell you what you really need to know with a 2 stroke. Only pressure/vacuum testing the cases will tell you if you have air leaks. If you do have an air leak it is only a matter of time before you have a meltdown. Leaking crank seals, intake manifolds, carb tops, powervalve seals and base gaskets are the usual issues. A compression test won't help you find any of them.

Consider it a lesson learned and start your rebuild. It is easier than you think. Do it properly. Use Yamaha parts where possible, including pistons and rings if your bore isn't larger than 64.50. If it is larger than that and you do need aftermarket pistons consider staying with cast pistons (Mitaka for example) rather than forged (Wiseco). Cast pistons will help you avoid uneven heat expansion issues and a 4 corner seizure. For a newbie that isn't racing the bike it is the easier way to go.

Now, pull the cylinders and see what lurks beneath. I would expect you to find molten aluminum has made its way into the rod and crank bearings. Buy a new crank. It will be the easiest option. Plenty available online. If you do all of the work yourself it will save you a lot of money, but the rebuild will never be cheap. About $900 Cdn for a new crank and a couple of piston kits. At least $200 for gaskets and seals. Then a rebore if necessary and cleaning up the head. Then any other parts needed such as water pump parts, thermostat, petcock, or any of the multitude of surprises that will surface. Budget at least $1500 Cdn if you do the work. Add another $1000 if someone else is doing it.

You can have your crank rebuilt, but after that meltdown and with at least 30K on the engine you'll be replacing the rods and all bearings, and then hope the webs are not worn or damaged. Rebuilding a wonky crank can cost more than new one, so just cut to the chase and buy a new one before you start.

It isn't rocket science. If you can read and follow directions you can do the job.

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Re: where to begin... looking for advice - RZ350

#12 Post by Backwoods » Thu Jul 06, 2017 4:59 am

Thanks for the reply. The pic is upside down it is the right cylinder.
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There is some aluminum below the exhaust port on the cylinder wall. I suppose it will depend on how much material has to come off to get a true bore again which will determine the new piston size. It is the original bore right now.

When they melt down does it always occur towards the exhaust port? Or is that indicative of the source of leakage? I haven't removed the cylinders yet as I may move the whole mess to another location for the rebuild. So I don't know what is going on in the bottom end yet. Is it at all possible that no material made it below the piston? I realize I may as well redo all the bottom bearings and seals, but is there any chance the crank can be saved? I have so many questions. Is there a preferred method for removing the material from the combustion chamber?
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I also forgot to mention that my temp gauge did not indicate any problem when she blew.

Josh

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