Rear cylinder rod bearrings frequently problem

[untaru22]

Hi, i`m new here . Sorry for my english.
I have a problem to my Yamaha xz 550 `82 . When i bought it all seems to be normal , but after i ride about 2000 km it started to make a weird noise and the oil light to light up when the engine idle (1000-1500 RPM) .I spread all the engine and i saw that the rod bearings at the rear cylinder are used so I changed it  and after more km this problem reapear. I think the intermediary exhaust is the problem because at the rear cylinder the exhaust is too short and the rear cylinder has a higher temperature . What do you think ? What i`m suposed to do ? :)
I have the exact problem like this guy in the video -->  https://www.youtube.com/watch?v=xYuHBRwNY-w 

P.S.: If i ride it and the temperature is going up it stops and i can start it up after is cooled

[tmyth79]

If rear cylinder is getting too hot I would look at a possible lean condition on that cylinder, either plugged/dirty carbs, or different jets needed, rear should be 2 sizes larger with stock exhaust, or a vaccum leak on that cylinder. Hope this helps.

[Rikugun]

The bike in the video suffers from low oil pressure which illuminates the oil light at idle. In the comments section the owner of the bike states:

"Actually found out the problem. The oil screen was filled with crap like RTV sealant from previous owners "fixes". The bike has been sold to a new owner that got this issue resolved and is now working on other gremlins that a bike this age tend to acquire."

There are a number of possible reasons why you have low oil pressure (if that is the problem) including a clogged pump inlet screen like in the video. Other possibilities are worn oil pump or incorrect sizing of the bearings when they were replaced.

[tmyth79]

I have not been able to watch the video but, from my automotive experience, low oil pressure will usually give noise and excessive wear on the top end of the engine first. If only one bearing is going bad I would check for properly sized bearings, crank journal condition, bent rod, misaligned piston to rod connection,  and oil passage blockages myself. As for the oil pressure problem, check the switch to make sure it's working properly, and if you have access to an oil pressure tester you test actual pressure.

[fret not]

Untaru22, where are you?  What is your native language?

[untaru22]

I`m from Romania.

[untaru22]

The bearrings has the correct size , the oil pump is checked , But if i  replace the rod bearrings again i`m affraid to happen  this again ... >:(  This is how happend : I was riding and i wanted to make right and it stopped and it don`t start. i pushed the bike to my parent`s house and i let it there. The next day i went there and i tried to start the engine and miraculously it starts and i wanted to let the bike to my garage . I ride it and when the engine`s got hot it started to make that noise and the rear cylinder was verry hot and the other one was a liitle bit hot

[Rikugun]

What makes you so sure the rod bearing has failed (again)? You are describing two issues - rod bearings and over heating rear cylinder - I'm not convinced the two are related. Are you certain the noise you hear is a failed rod bearing? They don't miraculously heal over night. Does your oil pressure light come on or is there just a knocking noise?

If the oil light comes on that obviously has to be addressed first. If not, I'd start with the overheating issue. What method are you using to determine one cylinder is hotter than the other? Has the temperature gage ever gone into the red zone?

[untaru22]

Is the same problem and thats why i think is again the rod bearings .  oil pressure light come on and is that noise at the same time. In the previous comment i wanted to say that after the engine was cooled the oil presure light was off but when it was getting hotter the light comes on . That`s why you said it was healing over night...the engine was cooled . My problem is EXACT like in the video and the noise too. I put my hand on both cylinders and that`s how I observe the temperature.

[jefferson]

If the seal on the end of the crank in the clutch cover is leaking it can cause low oil pressure. They can get boogered up when the clutch cover is put back on or removed for that matter. I spun 2 rear cyl. rod bearing on 2 different motors. The common denominator was both engines were running hot. Poor quality bearings is the crux of the problem and there are some posts about using some Mazda bearings to upgrade. I have no idea why it is always the rear cylinder. The temps I took actually showed the rear cyl. runs cooler than the front due to the increased coolant flow to the rear cylinder. The coolant flow to your rear cylinder may be impaired somehow. Is the temp gauge showing the engine getting hot?

Jeff

[Rikugun]

Thanks for posting Jefferson. The clutch cover seal is a good place to look that I didn't even consider.

Tell me more about the heat issues you were having with the 2 failed bearings. Do you feel heat caused low oil pressure or low oil pressure caused it to run hot?

How hot is hot? Was the gage in the red?

[jefferson]

Both of my overheat issues were on the track and not due to low oil pressure. That came after the bearings spun. One of the overheats was due to a stuck thermostat and I really don't recall the other. I noticed that the engine was getting too warm and I backed off and started cruising, but didn't make it back before the rod bearing spun. I don't recall whether the gauge had made it into the red or not. The oil shouldn't have been too warm as I was only on the the 3rd or 4th lap of practice and I hadn't been really flogging the thing. The engine was the 680 out of Joe Fischers race bike and I was just really feeling things out on it when I noticed it getting hot. I sure wish I had noticed on the lap prior to the bearing lunch so I could have pulled in before it happened.

Jeff

[QBS]

Jefferson, does your bike have a Texas history?

[jefferson]

The engine and a bunch of parts came from Joe in Dime Box. The bike I took the engine out of I sold.

[QBS]

Amazing!  I met Joe at his store in '86.  We talked Vision modifications etc.  He claimed that Yamaha had given him a factory built 750cc Vision engine to race.  He showed me a Vision carb that had its' throat machined out to 42mm.  He said Visions were very competitive racers  right out of the box, totally stock.

[jefferson]

Eddie ended up with that 750. I tried, but it had already been promised to him. The carb on this 680 was modified quite a bit. I haven't measured it, but it may be the one you saw. It really doesn't work very well on a stock size motor.
I can attest to that last statement.