Bad piston rings question repair or replace

[van avery]

I have a ring problem with my 83 xvz12. Starting new thread on this.

I put #2 cylinder at TDC and pressurized ( 5 to10 PSI) on that cylinder and could hear the air at the oil filler spout.

Rechecked the compression on all cylinders and had 180psi on #1 , 80psi on #2, 150psi on #3 and 110psi on #4.

By the time I buy new rings, gaskets, rework heads, check valve adjustment, etc.. It looks like I might be better to purchase used engine off Ebay and change out.

I've spent too much time and hours on this bike to give up. The mechanic I had look at it recommended just keep riding it. It starts OK but when idleing will stumble several times and die and when under 3000RPM accelerating the engine belches several times.

I've already replace plugs, wires and caps, new aftermarket TCI, replaced battery cables, repair brakes, new Deka battery, etc.

Looking for some advice or really good deal on engine.

[Flyinfool]

I can't believe that low compression in one cylinder would cause that much problem.

There are many here (me included:whistling:) that have inadvertently left off 1 spark plug wire and rode quite a while before noticing the loss of power or change in the idle. That low compression cylinder should still be working, just not as hard.

 

You should also look into why it is low on compression, Do you have a carb issue that is dumping gas in that cylinder and washing the oil off the walls? Is your oil level rising? Does your oil smell like gas? There is usually some reason for the rings in just one cyl to go bad.

[twigg]

Those pressures are all over the place, and pretty much nothing is normal about them.

 

It can be very tricky to measure compression accurately, so check your method and do it with the engine hot and the throttle wide open.

 

Not disputing you, just sayin' that those readings don't make a great deal of sense.

 

You might also check the valve clearances before you rip the engine apart, or out. It could be as simple as the valves not fully closing.

[Yammer Dan]

Valve too tight?

[Condor]

Valve too tight?

 

[SilvrT]

I put #2 cylinder at TDC and pressurized ( 5 to10 PSI) on that cylinder and could hear the air at the oil filler spout.

 

 

It could be as simple as the valves not fully closing.

 

If the valves were not sealing (closing) but the rings were, then why would air pressure be coming out the oil filler spout ... it should either be coming out the carbs or the exhaust ...Yes/No???

[Yammer Dan]

Don't you know everybody hates a...... humm you could be right:whistling: Gotta start thinking before answering!!

[twigg]

If the valves were not sealing (closing) but the rings were, then why would air pressure be coming out the oil filler spout ... it should either be coming out the carbs or the exhaust ...Yes/No???

 

Yes ... and No

 

Doncha just love the simple life.

 

The problem here is that you have four cylinders, and four wildly different compression readings.

 

When an engine wears (what's the mileage?) then it generally does so in a fairly uniform manner. So the pressures would fall over time, but evenly. This is varied by a number of factors .... Rear cylinders run a bit hotter, so may wear faster, etc.

 

So when you get three cylinders at a lowish but even pressure, and one outlier at, say 80psi, then it's a straightforward job to know where to start looking.

 

Secondly, I'd argue that 5 to 10 psi pressure isn't enough to accurately identify where the air is escaping, even if you can apparently hear some coming from the oil filler.

 

The wide disparity of your readings point to either technique with the compression tester (this is not a criticism), or some bad news in the valve department.

 

The way to find out which is to do a "leakdown test". In that test the pressure used is about 100psi, and there will be no doubt at all where the air is escaping. Some leakage is normal, but shout be in about the 4% range, and anything over 10% would need investigating.

 

I am trying to help here, and I would suggest you do two things ....

 

First check the valve clearances, then do a leakdown test.

 

Let us know what you find.

[jurob]

Did you put oil in the affected cylinders after doing the test?

 

It is odd that you have 3 possibly bad cylinders at varying levels of wear.

 

What I like to do is remove the gauge and the schrader valve and blow into the the cylinder and listen carefully to isolate where the leak is.

 

When you say belching, out of the carb or?

[bongobobny]

The problem with buying another engine off Fleabay is you may get one in no better shape than you already have and end up doing a rebuild anyway. If you do a rebuild you are going to end up with a strong engine that will keep running for a real long time...

[bkuhr]

some air will escape around the rings. thats what you need to do "leak down test".

apply continous air source and monitor how much pressure drops of other end of leak down manifold. then you can crank air up at manifold, listening for where air is leaking.

also adding oil will form temporary seal around rings. If with oil, pressure shoot way up then it is rings, if no change then likely valves/head.

 

somewhere here I have a post with my leakdown readings, I will try to find it.

http://www.venturerider.org/forum/showthread.php?t=46640

 

One thing to remember is the compression pressure is highly dependant on the timing of the valves. If a valve opens or to early or closes to late in the compression cycle, you will NOT build the full compression. A likely reason for for valve timing to be off is valve gap being too tight(not enough commpression) or too loose(too much commpression). With our bikes, the valve shims are known to wear causing less gap there for less commpression.

Edited August 10, 2011 by bkuhr
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[BradT]

The problem with buying another engine off Fleabay is you may get one in no better shape than you already have and end up doing a rebuild anyway. ..

 

Agree with this statement. The amount of work to rebuild is not that much more than changing the engine, then you know what you have.

 

Brad

[van avery]

The mechanic said his results were that 1 and 3 had 180 PSI and 2 and 4 has 80 PSI. He noted that the plugs in 2 and 4 cylinders had an oily odor. He told me that the rings were bad. I’ve also noted slight oil on those plugs.

Yesterday the compression test I did was with a cold engine and throttle closed.

Forgot to mention earlier I cleaned the carbs last year and again this last month. I also replaced the diaphragms on the carbs.

Anyway , this morning I started to redo the compression test and while warming up the bike noticed that the slider in #4 was not moving like the others so moved it to another carb and the problem moved. Finally found a small tear at the edge of the diaphragm and replaced it with another diaphragm and that seemed to help, the sliders all look like they are working together. The idle stumbles but at least now does not die after several stumbles. Also, when reving the engine then letting off looking down the throat noted small fire expelling in # 3 carb once in a while ( when it burps). Looks like maybe valve adjustment.

I also put around 80 PSI on # 2 cylinder and could hear air coming from the carb, and a little from the oil filler.

This evening I re ran the compression test hopefully correctly (warmed up engine, pulled all plugs, opened throttle completely ) and had the following readings: Opening the throttle made a big difference.

190 psi on 1

180 psi on 2

155 psi on 3

180 psi on 4

Looks like maybe valve adjustment. I’ll have to open covers and check clearances. Looks like #3 inlet valve is opening too early causing the burping in that cylinder and the fire in the throat. Haven't use my feeler gauges since I had a VW thing about 25 years ago.

To answer a couple of questions. The oil level is not rising and I really don't smell a gas ordor in the oil.

Thanks again for the input guy's, I'll let you know what I find. Might be a day or so before I get back to it.

Edited August 11, 2011 by van avery

[twigg]

That looks rather better

 

You will always hear "some" air getting by the rings, but you shouldn't hear any through the carbs or the exhaust. They will lose maybe 4 or 5% and that goes into the crankcase.

 

The one cylinder that is low is where you will most likely find a valve too tight.

 

Good luck with it, but it all sounds a bit more hopeful.

 

ps .... You won't want to run the engine too much before fixing this. If it's an exhaust valve that isn't fully closing then the danger is that the hot compression gasses escape past the valve. The valve overheats and can burn. Then you need to remove the head to replace or re-lap it.

[van avery]

Pulled the back valve cover and checked the valves on # 1 and #3. The intake valves on Number 3 are definately too tight. Have to adjust and hopefully things will get better.

[Yammer Dan]

Valve too tight?

 

 

 

 

Can I say it??? Can I? Can I?

 

 

Glad it is looking that way. Whole lot cheaper than rebuild.

 

 

OK I won't say it.....

[van avery]

Go ahead and say it before ya pop. Good call.

[Yammer Dan]

I'm over it now. Glad you got it figgured out.:clap2:

 

 

Let us know how it comes out.

Edited August 14, 2011 by Yammer Dan

[jasonm.]

Go ahead and say it before ya pop. Good call.

Glad to hear another being kept alive. Hope you have the valve tool. It's a must have...

[van avery]

Quick update, I adjusted the valves and 10 of them were too tight. Thanks to Perry for the loan of the shim kit.

After adjustment the compression reading were #1 -195, #2 – 190 , #3 – 195, 4-180. Sure doesn’t need a ring job.

Bike will now idle fairly consistently at 1000 to 1100 RPM. Much improved. Not doing the “belching back” on acceleration.

It is running hot yet. Down the road it runs just below the red ( a little above ¾ of the green) but when waiting for a traffic light it eases up to the red line. Fan doesn’t come on until the temperature gauge is hitting the red.

I pulled the radiator and had it cleaned, pulled the thermostat and tested and was fully open at around 190F. I pulled the cylinder side covers a pulled the small rubber plugs a flushed the motor then replaced the antifreeze. Yes, I turned the small valve in front to “on” while filling system and then cycled it while running to make sure the system was full then turned back to “off” to ride. Installed new Radiator cap, finished filling the overflow tank to the fill line.

It is around 100 Deg out and I did leave the side covers off the bike while doing the test ride about 13 miles .

Any idea what else to do?

Should I install a fan bypass switch?

Thanks again guy's for the help.

[SilvrT]

a lot of the 1st gen temp gauges read that way ... high on the gauge, and as such, one would think they were running hot... when in fact they're not. Both my '85 and '87 read high ... the '85 was like your's. It never overheated... nor did my '87.

 

This has been talked about several times here and I just learned to trust what everyone was saying (basically what I just said) and not be concerned abou it.

[Freebird]

Yes, and if I remember correctly, the early year were even worse. Most, if not all, of them read like they were running hot. I was told that it was normal but that Yamaha heard about it so much that they re-calibrated the temp gauges on later year models so that they did not APPEAR to run as hot.

[bilko1]

Yes, and if I remember correctly, the early year were even worse. Most, if not all, of them read like they were running hot. I was told that it was normal but that Yamaha heard about it so much that they re-calibrated the temp gauges on later year models so that they did not APPEAR to run as hot.

 

What would the real temp. be at the temp sending unit, if taken with a noncontact temp indecator?

My 83 used to run a little above 1/2 way up the guage, now its slightley higher then 2/3rd's the way up the guage.

[frankd]

What everybody has told you is absolutely correct. Mk 1's temperature gauges read a bit higher than Mk II's. If it's 100 degrees out, any First Gen (I have no idea about 2nd Gens) would run a bit hot. I have an 83 also, and before I did the 2nd gear repair it would run almost up to the red line if it was over 90. When I put it back together, it ran much cooler. The only thing I could think of that would explain this was it was much cleaner. Before I took it apart, the motor was a bit grimy, and I cleaned everything while it was apart. Clean yours engine as much as possible, especially the front and bottom and yours will cool down a bit.

 

Frank D.

[bkuhr]

I had made the mistake of topping off the system thru the coolant bottle. Only problem was overflow tube from radiator to bottle was plugged, and I never had radiator topped off.

 

Suggest pull the overflow tube at the radiator, bottle should drain immeadiatly. Also make sure you can blow air thru radiator overflow nipple with pressure cap off.

 

I also replaced my pressure cap.

 

I ran just under red even stopped in traffic after correcting these items. Prior to this I was middle red.