Serious problem.....

[spldart]

I picked up a 83 vision a few months ago cuz I needed a motorcycle's cheap gas/cheap insurance to get to a job that's a bit far way in a commute that a motorcycle is singularly suited for.
The bike has 25.5 k miles on it.
My first order of business was to change the somewhat nasty oil in it. Then modify the charge system by putting the R/R assy out near the swingarm.
I also had an issue with wiring causing intermittant failures here and there so went through and took care of those a bit too.

Tuesday. On my way back from work in the HOV lane at about 62 miles an hour I started losing power just a bit ( and I'm not talking the tach overev drop out issue. I already took care of that)

So I pull off the freeway and get my helmet off. Start it back up and I got metalic sounds from the rear cyl/head assy. Ticking and tapping... Almost a combo of a lifter tick and a piston slap.
Ok... The bike is home now and I have the carbs, inlets, plugs out and I did a compression test. Front cyl 130 psi and rear in the 80's.
I also notice in my testing that the rear carbs overflow is dripping whenever fuel is on. IE prime or on with motor started. This is a brand new symptom.
I fixed the carb overflow problem but the engine is still behaving just as it was. Down on power and rear jug area noisy.

I'm a bit disturbed as this engine is awefully young (measured in miles) to be having this kind of failure.
I have one more test I'm doing tomorrow and that is to dump a little bit of fresh oil on top of the cylinder near the wall at the highest point.... and then rerun the compression test.
I know if the valves are the problem this wont effect the compression test but if it's piston rings this will cause the compression test to jump significantly in psi.

Any thoughts?
Am I out a motorcycle?
Are these engine worth rebuilding?
The last bike I rebuilt had sentimental value so I ended up paying double the bike purchase price used on the engine rebuild ( and this is with me turning the wrench )

Thanks for any input.

[Hellgate]

It's 30 years old...

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[spldart]

It is old. But surely that really only counts towards wear and tear on things like seals that break down with age. The mileage however....
A low mile motor is a low mile motor is it not? Oil leaks not withstanding.
Have I missed anything in diagnosis?

[Hellgate]

Rust

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[spldart]

Ok... Your just a troll. Any real input please? Never mind the guy above.

[dingleberry]

maybe the rear carby float height has been washing the bore resulting in a less lubed piston/rings - early wear. If oil not present on bore when stored this could result in rust which would cause rapid wear when run or broken ring?   

[Rikugun]

How many miles have you put on the bike before this happened? Any external leaks (oil or water) or smoke from the exhaust? Is the oil free from coolant contamination? Any evidence of excessive blow-by i.e. oil and gunk in the airbox?

A leakdown test would help narrow the possibilities between valve/ring issues. Regardless of where the problem lie, sudden loss of power, low compression numbers and mechanical noises spell top end disassembly to some degree. Have you considered removing the valve covers and taking a peek inside?

Depending on the severity of the repair it often makes sense to find a parts bike with a sound engine. Some parts are unavailable and the remaining can be more than the $ of a parts bike. If you do end up tearing it apart, search Jimustanguitar posts for aftermarket head gaskets. NOS Piston and ring sets are sometimes on Ebay but rarely in combinations that are helpful and again very $.

Sorry you are having these problems and hopefully it can be resolved with as little trouble as possible. :)

[Walt_M.]

Could be the cam chain tensioner. Hard to say without more history like how long it ran/sat with the crappy oil. The rear rod bearings have proven somewhat of a failure area and could be the source of the knock but wouldn't necessarily cause the low pressure unless something damaged the cylinder. About all I can offer is encouragement.

[spldart]

I appreciate the more technical responses.
The carb overflow is a very very recent issue. It's resolved.
I have 1400 miles on it from when I bought in.
I fell back on my old school mechanic training... I took a coffee straw. Dipped it in some fresh yamalube 20/50 and dabbed it around the
outskirts of the piston in the cylinder that is low on compression using the spark plug hole. Then immeadiately did another compression test.
It, the compression, jumped substantially. This tells me it's not a valve issue but a piston ring issue.
I then dumped the oil that only has several hundred miles on it and I found steel filings, they stick to magnet.  :-\
I went ahead and changed the oil and filter again and started, but did not finish, reassembly.
I'm thinking that fresh oil and filter and keeping the bike in the local area, low revs, means I can still ride for a bit longer before it expires.
I'm assuming I just came into this motor at an inopportune moment as I was babying it because my need was great.
Oh well. The motor is still impressive and ahead of it's time.

[fret not]

If you still have the old oil filter you can cut it open to actually see what it has been removing from the oil system.  If the oil filter gets too much debris in it the oil flow is restricted and the pressure relief valve opens and everything goes through the oil system.  Just a thought.

It might be time to start looking for a replacement cylinder.  If I were looking for one I would start in the SWAP SHOP and ask for availability.

[spldart]

The drain plug is the style with a magnet in the end. The size of the metal chunks are the largest I've ever seen out of an engine, that still runs,
so I know it's bad. May I assume that if I'm looking for a new cylinder that and overbore and new pistons .5mm to 1mm overbore are not an
option due to lack of availability?
The oil filter has been set aside to throughly drain so I can do just that... Dissect it for further sign of what damage I'm facing. Very good
advice. Glad I did set it aside for inspection already.
I remember reading elsewhere that someone found a place that has all kinds of piston rings and he was able to get new ones for his vision.
I'm kinda barely considering ordering rings and buying a new hone and get after it shade tree style. But that is down the road due to lack of funds.
I've had a long string of tragedies hit me recently.

Thanks again for the tech input. I hope to get the carbs mounted again this evening and get it started.

PS: And no. I don't consider the blown bike engine a tragedy. It's just a very serious inconvenience that causes other more serious issue to be
aggravated.  :-\

[fret not]

Rather than going to the expense of buying new parts I suggest looking for used parts, like from a functional motor.  A set of cylinder and piston with rings that ran together would be what I would look for.  You might find a motor to 'borrow' parts from for the motor in your bike, or exchange the 'new' motor for the one in your bike.

If you are going to use the original motor you need to take it apart and clean it or risk nearly certain damage and demise.  Metal parts flowing in the oil will certainly find their way to the rod bearings, which are already under designed.  They will also lurk in the transmission and all it's many nooks and crannies.

I wonder what happened in your motor.  It could possibly be from the starter clutch, cam chain tensioners, broken rings, or any number of issues.  You have to take it apart it to see.

[spldart]

My guess is rings. Brought about by overheating twice in this nasty south east texas summer. I quickly worked on the bike and my riding style to get this issue under control but since that rear jug is DEFINITELY an issue with getting to hot I'm thinking this is what happened.
If I do a tear down I will definitely post what I find. It wouldn't be the 15th engine I have done so... Or the 20th.
Good advice there too. Either clean ridiculously to the nth degree before mounting 'new' used parts or just swap to a 'new' engine that produces a good compression test number.
I am still considering getting some rings from the one place, hone the crap out of the weak cyl then break it in and hope for the best for a bike I can take out once in a while for fun.
Already looking at a garaged Kawi Ninja for a possible next commuter if the price can be negotiated to a reasonable number.

Thanks so much guys.

[jefferson]

Since it is the rear cyl. I am going with a spun rod bearing. I had 2 engines do that, but only when running hot. Just thought I would throw that out there.

Jeff

[Re-Vision]

Spidart, contact me at bobbydcrabb1@yahoo.com  I may be able to offer some help.    BDC

[spldart]

Spun rod bearing? These things don't have full roller bearings at rod ends? I gotta open my service manual :( hehe.

[Walt_M.]

There is a new rod bearing on ebay for $20 right now. Also lots of other engine parts on there. If you have some time you might want to do some browsing. I almost bought the bearing just to have but I remembered you might need it.

[zore]

Age kills all eventually.  If you aren't sure how it was stored or cared for it could have been on it's way out 10k ago.