lower connecting rod bearing replacement

I have the beginnings of what I suspect may be a lower connecting rod knock on my KZ750E (4 cyl). This is a bike that was badly abused, and was sold to me from behind a frat house at UC Berkeley, where it had been sitting for a long time. I suspect the PO didn't conduct regular maintenance, and probably ran the ___ out of it willy nilly.

When I first got it, I cleaned it up and did a repaint (appologies Ron -- the tank was a dented weathered mess). Plus I went over all the safety items on the bike, but didn't need to get into the engine internals, which seemd fine after the carbs were cleaned up. It pulls strong over the full range in all gears, right up to about 102 MPH, where I decided that was adequate for my pruposes.

I have put about 5,000 miles on it since I got it (now about 29,000 miles total on the OD). I just use the bike as a spare ride, and sometimes my son takes it out for around the town errands. It is not a showboat, but it looks good, is fun to ride, and is worth a little bit of effort to check out and maybe fix this knock problem.

I plan on taking the pan off to investigate this knock (when I get time), but I have a fair amount of spare engine parts, and thought I might swap in a used pair of rod bearing shells from my stash while I am in there if I find too much clearance on the existing bearing. Yes, I know I need to test for clearances, and I plan to do that.

Does anybody here think this is not a good idea? I hope I can do this through the bottom end/ oil pan opening, and not need to disassemble the top end or split the cases. Am I totally ignorant of what might be involved in this? Yes, but that's why I have you guys around to keep me straight.
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Post edited by: apeman, at: 2007/03/14 18:35

I bet most people are going to tell you to use new bearing shells, but not me

If you have good bearing shells that have the proper clearance, then I'd use them, new or old, the motor don't care.

I have to ask though, are you sure it's not the primary chain making noise?

Also, keep in mind that if the bearings were damaged by neglect, every other bearing surface in the motor faced the same neglect.

Post edited by: steell, at: 2007/03/14 19:38

x2 on the primary chain.
I’d think the main and the rods would be the first to get oil, so that the cam bearing would take the brunt of poor maintenance

Im with you on that Steel! I switched the rod bearings 3 and 4 and they had good oil clearances, so I put the engine back together and that was all she wrote. 650 is running as strong as it was a year after it was born

if the crank isnt chewed up and youve got a set of bearings with good clearances id say go for it also.it sounds like its just a backup bike thats not getting hammered across the globe so it shouldnt be a problem.back in the good ol days of babbit bearings poured into the block you could cheat and put a thin piece of lead on the bearing caps and make your own poormans bearings,steele has probably seen that trick im sure:evil: i have never worked on a bike with a primary chain so i cant help with that idea!

I have heard of someone using a tin can back in the Bahamas where things are expensive and rare

To all who have given their input, thank you. I was hoping to start this project over the seekend, but I need to do my taxes, so it looks like the bike needs to wait a little.

If it is a connecting rod bearing, I will try using a "preowned" replacment. I thought that would be the way to do it.

This IS something I can do through the oil pan openning, right?

yep just be carefull spinning the top bearing half off soo you dont nick the crank,rubber hose on rod bolts works good.mark any rod caps you remove with a number and arrow so it goes back on the right way;)

I would go for the number 4 crank first. Trust me! Saves you alot of time looking for the extra oil clearance

I was going to say try # 2 first. That's the one I've lost before.
Mark

Well, from looking at various pictures, it seems I cannot reach the outer rod bearing caps without splitting the cases. I am a firm believer in not taking things apart when you don't need to, and I really do not want to remove the engine, nor disassemble the upper engine, if I do not need to. Here is my idea:

1. Remove the seat, tank and battery;
2. Turn the bike upside down, so it is resting on its handlebars and the rear frame "belly-up";
3. Remove the oil pan and the bottom half of the engine cases;
4. remove the bearing caps and inspect/measure the crank and rod bearings -- replace or repair as needed;
5. reassemble.

If this proceedure works, I figure it will save me many hours of time that would be wasted in removing the engine and disassembling the entire thing, top to bottom. I just want to focus on my lower end noise issue.

The hardest part part will be wrestling the bike to the upside down position, but that will not be any harder than trying to muscle the engine in and out. Besides, I have the help of my 22 year old son who lifts weights and plays rugby. (He has bench pressed 360#.) Between the two of us we should be able to muscle the bike into position.

Waddayathink?