Knocking noise on 82 kz550 LTD C3

Hey guys, i'm the proud new owner of a 82 kz550 LTD C3! I've dug into a few 4cyl engines in those 4 wheeled vehicles but this is my first motorcycle.

I got her running after cleaning the carbs and fixing the previous owner's hackjob on the sparkplugs, but now im dealing with a knocking noise. First off, here's a video.

-By feel the knocking feels like its centered around the intake cam cover on the left side.
-Varies with RPM
-It is running 5W-30 oil as that's all i had on hand and just wanted to verify the engine ran.
-does not change with clutch position.

I pulled the valve cover and didn't see anything immediately wrong with the suspected area. I checked all valve clearances and found them to be .004 in on the intake and .006 in on the exhaust... so the bare minimum of the spec. i removed the tensioner, installed the valve cover and reset the tensioner. Engine sounded better so i killed it, pulled it out of the garage and started it to take it for a short ride. knock was immediately more noticeable on second start. the clutch was dragging a bit on start so I drove around a bit and noticed the the clutch was slipping at higher load as well.

I was heading home and the bike suddenly dies and will not crank over again. Battery was not dead. I pulled the spark plugs, valve cover and timing advance cover. I would say it wasn't overheated as i didn't burn myself getting the valvecover off (first air cooled engine so i don't know what feels normal). Valves looked ok so i put a bit more weight on the crankbolt and got it to turn over to check the timing marks which turned out to be spot on as before. Turns over pretty hard though and one particular spot in that rotation is harder than the rest. I pulled the starter and removed the clutch cable and still had the same issue.

knocking has never been audible cranking by hand. There has always been a slight knock when initially starting to turn the crank but i assumed this was just the gears meshing. it only happens when jerking the crank a bit, not under slow rotation.

Before these weird hard turn over issues I was pretty sure a manual chain tensioner would fix it as the noise decreased when the tensioner was reset. Now i'm not really sure what the issue is.

Sounds like the top end. Not sure what to suggest though. Hope that car oil you installed was not the "energy conserving " type or you may have contaminated the clutch plates.

Sounds more like a rod bearing is shot on the crank.

Nessism wrote: Sounds like the top end. Not sure what to suggest though. Hope that car oil you installed was not the "energy conserving " type or you may have contaminated the clutch plates.

It has Mobil 5-30 conventional in it so that's probably the clutch issue. i have some 10w-40 as called for in the manual that will be here soon.

Sounds more like a rod bearing is shot on the crank.

I think the plan now is to drop the pan, get rid of the shitty 5-30, check the chain tensioner guide, and isntall the manual tensioner. Ill check out the rods when i'm down there, but the noise was more focused in the top end (i hope so! but this bike wasnt in the best of condition)

Have you done a compression test or even a leakdown test?
Was it running on all 4 cylinders?
Are all 4 choke flaps intact?

All of those questions are focused on the possibility a choke flap got stuck in one of the valves. If so, the valve would not close all the way and the cam would bang on the valve when it comes time to open it. Since it would not be sealing, that cylinder probably would not run well if at all. A compression test or leakdown test would show the faulty valve issue.

Fist thing would be to look at the choke plates, They can be taken out from the top. You don't need to remove the carbs to check them.

The weird thing is 90% of the flaps somehow make it through the engine. every once in a while, one gets caught in a valve.

Here's a link about the flaps:
s3.amazonaws.com/gpzweb/TK22mainPage/TK2...chokePlateFlaps.html

loudhvx wrote: Have you done a compression test or even a leakdown test?
Was it running on all 4 cylinders?
Are all 4 choke flaps intact?

A compression test was one of the first things I wanted to do but I couldn't find a tester with a 12mmx1.25 adapter for the smaller plug holes on these engines... ill be doing this soon. The last time it was running, it was running very well. started on first start and sounded like it was firing all right on all 4.

there was one choke flap missing when i got the bike. i gotta pull the carbs to get that tensioner out so ill check them again then. but wouldn't i have found some out of whack valve clearance measurements if one was stuck this whole time?

loudhvx wrote: The weird thing is 90% of the flaps somehow make it through the engine. every once in a while, one gets caught in a valve.

Unbelievable that this could be happen so often without a valve or piston damage!!!!
The right valve and piston timing made it possible.

I wouldn't be so quick to say no damage...

I find it rare to find all flaps in tact on a Kz550 (the later motors used different carbs without flaps). And yet, I've never come across a 550 where there was any remnant of a flap in the motor, or any ill symptom from it (but there have been a few on Kzrider). The flap can really only go one way, and that's through the motor. It does still baffle me completely. One bike I bought had three of four flaps missing. I've been riding that bike for 17 years now.

Saablord wrote: ...
The last time it was running, it was running very well. started on first start and sounded like it was firing all right on all 4.

there was one choke flap missing when i got the bike. i gotta pull the carbs to get that tensioner out so ill check them again then. but wouldn't i have found some out of whack valve clearance measurements if one was stuck this whole time?

Yes. If a flap was stuck in the valve it would throw off the valve clearance. I wonder if the flap is not there, but the valve may be slightly bent and possibly sticks. That could explain the knocking sound and possibly the tight rotation spot.

I don't think I'd change the tensioner. As long as it's working there really isn't a need. There isn't really a history of those going bad on the early 550's. I think the issue with the valve cover is what make people want to go with a manual tensioner.

But your real task, I would think, is to find the source of the knocking noise and the tight spot on the crank rotation, and the overall tightness in the rotation.

I would pull all four plugs, so you don't have to fight with compression, and mark the position of the tight spot to make sure it's always at the same spot. Then set it to that position and remove the valve cover to see what valves are being pressed.

I would also rotate the motor with the cover off to see if any of the valves seem to jump (as if they are sticking).

The overall drag on the crank rotation is strange, as is the sudden stop of the motor.

Yes. If a flap was stuck in the valve it would throw off the valve clearance. I wonder if the flap is not there, but the valve may be slightly bent and possibly sticks. That could explain the knocking sound and possibly the tight rotation spot.

Hmm now that i think about it, this is very likely! maybe that valve has been bent since that flap was eaten as the carb that has the missing flap is the one that feeds the noisey valve/cylinder or whatever. valve clearance was ok though.

I don't think I'd change the tensioner. As long as it's working there really isn't a need. There isn't really a history of those going bad on the early 550's. I think the issue with the valve cover is what make people want to go with a manual tensioner.

oh well, its already on the way and i dont know for sure that it is working correctly as the noise seemed to quite down after resetting the tensioner. i have a new gasket set so it wont hurt and may help find the noise.
I don't know what all the fuss is about with the valve cover issue. just take off the cap on the tensioner, put the valve cover back on, put the cap back on. done.

But your real task, I would think, is to find the source of the knocking noise and the tight spot on the crank rotation, and the overall tightness in the rotation. The overall drag on the crank rotation is strange, as is the sudden stop of the motor.

yup, this only adds to the complexity of the issue. really weird.

I would pull all four plugs, so you don't have to fight with compression, and mark the position of the tight spot to make sure it's always at the same spot. Then set it to that position and remove the valve cover to see what valves are being pressed.

I would also rotate the motor with the cover off to see if any of the valves seem to jump (as if they are sticking).

plugs were already out and it was hard to turn... so even worse.
ill add this to the list.

A bunch of parts are coming in on friday so ill be able to eliminate quite a few things hopefully. Thanks for new ideas.

Scirocco wrote: Sounds more like a rod bearing is shot on the crank.

ding ding ding! we have a winner I think. Pulled the oil pan.....


uh oh...


shit shit shit


thought so.


might as well pull the motor.....

i'm guessing it was a rod bearing/crank bearing locking up that caused the sudden seizing of the motor.

So! thoughts on where to go from here? I'm now at the point where it would have been cheaper just to buy a running motorcycle (got this for $175), but its too late for that. First thought was to pull the crank figure out what went wrong and have it checked over / machined and get new bearings. I'd pull the head as well just to verify that the valves are ok.

You can't machine one of those cranks. There are no undersized bearings available. It shouldn't be overly hard to find a good used crank though. You gotta pay attention to the marks on the crankcase and the marks on the crank and then order the proper size/color bearings. The FSM details what's needed in that regard.