1986 XT600 Noise after 3/4 to full throttle
 

Hey guys like I said it’s a noise that only happens under load and it’s almost like piston slap. It sounds deep inside the motor like around the carb area. It only happens after I get on it maybe 1/2 throttle closer to 3/4 throttle.

It kept happening until the head gasket started blowing out the compression and most of oil all over my right leg. The bike still runs but you have to run it light and slow. I’m not running it anymore until I change the head gasket but I want to know what that noise is. As I don’t want to change the hg just for it to happen again and mess up the new hg.

Notice when I took off the rocker cover the two head bolts on the exhaust side were LOOSE and the leak was on the exhaust side (by exhaust side I mean right side where the exhaust is routed.)I tightened those bolts up put the cover back on and the oil leaking got a little better. But eventually came back. Can this be a timing problem? Can being a tooth off timing make that noise and blow a hg? Any help from the xt gurus would be greatly appreciated. Just waiting for some insight before replacing the hg.

Also when I’m idling and I give it a quick blip of throttle it makes this horrid metal noise just as soon as I crack the throttle like piston slap. Only happens when I give it a good blip does not happen when I roll on the throttle more smoothly.

try to load a youtube video where you can hear the issue, MIGHT help, but could be so many things.


if the bike has been ok before, not a chance that cam jumped a tooth.


only thing to check easily is the crankshaft nut on the right, sometimes it gets loose. if its not that, then its top end off to find the cause

It’s always done that noise since I bought it a couple months back. I just didn’t hear it because it wouldn’t get that high in rpm until I fixed the carb issue. I’m thinking piston slap or pre detonation.

Is it normal for a blown hg to leak oil or do I have blow by?

I’ll try to upload a better video of the sound as this is just the sound of the blown hg.

https://youtu.be/oCnMZZghnfA

Wow that`s a leak. :eek3:

So you need to do the head gasket for sure, as for your other "knock" check out THIS post i made several years ago.

Mezo.

I’m definitely changing the hg tomorrow actually I just didn’t want it to go bad again. I’ll see if once I change the hg it keeps doing the knock. I’ll get a vid of it. I saw the post you mentioned and it’s not that. The knock is so strange. At first I thought it was the front fender rubbing against the tire, then I thought it was the butterfly o the carb flapping away because it would go over 180 degrees at wot. That wasn’t it either. I’m honestly stumped. We’ll see tomorrow if it keeps making the noise.


Little update
Took off the cylinder head to change hg and found 2 bolts had helicoils but they were stripped. Put new ones in new head gasket in torqued down to 20 ft lbs and low and behold same issue. It’s leaking the compression through right side hg. It’s tons better than before and i don’t think it’s leaking oil yet...

I made sure to clean the mating surfaces well but looks like I will have to resurface them as it looks to have had some warpage on the right side. Hopefully it will hold up a bit longer until I can do everything properly with time but I need the bike running as it’s my only means on transport.

Anywho this thing runs no matter what. I love the old reliable steel steed. Here are some pics.

Does anyone know what the hose on top of the rocker cover does? It this a vent tube for the oil tank?

For some reason I have oil leaking from there. I follow that hose back to the upper part of the oil tank.

Can you take a picture of it where it goes in to the rocker cover.

Mezo.

I see it oozing out of the top of the rocker cover not sure if it’s coming from the rocker cover or the oil tank.

I see it oozing out of the top of the rocker cover not sure if it’s coming from the rocker cover or the oil tank.

would connect it to the airbox. try to see if airbox has a tube nipple thats not connected to anything besides the water drain at the bottom...


even if compression leak is small, it will deteriorate fast and strand you...
you have to send both cyl and head for a minimum flat surfacing and make sure all cyl head bolt threads are super healthy. hope you are using a torque wrench too.

no shortcuts if you want to solve this properly.



and of course, dont reuse the hg....

Yeah I’m gonna take it apart again and resurface the head and make sure the head bolts have healthy threads. The hose I talking about goes from the oil tank to the top of the rocker cover. Here’s another picture.


Also when setting up the timing chain for some reason when I put the crank mark at tdc and the piston isn’t at tdc so the marks are useless. Now I’m afraid I have it off timing. Is it possible for the crank marks to be off?

Yes thats the oil tank vent hose that goes into rocker cover. If you overfill oil tank you will get oil pumping through that hose rather than oil vapor.

You are looking at the TDC mark on the flywheel and not the timing mark? Is possible crank camchain gear or flywheel has spun slightly. Will need to remove the flywheel and check keyway is still intact and check dot on the crank cam gear is at 12 oclock position at TDC. Might explain the noise you were having at the start. Timing way off causing bad knocking/ pinging?



I used to be of that thinking....I have a 3TB that have had a few issues with and have used same head gasket and base gasket 3 times and has done lots of kms since last torqued down.. Both genuine Yam gaskets. Wouldn't attempt that with aftermarket items though!

i meant he shouldnt reuse a gasket that already has been leaking compression like in his case, no way it going to work well again

DZL, if you had just some oil leak, i can understand reusing it...

but it's apples and oranges...



the cam chain wheel on the crank is a super strong press fit on the shaft, there is no keyway, not sure why you are saying this
never ever saw one that shifted. sounds like something is wrong in RSC's alignment process

Ok so I’m looking at the mark above the crank. The flywheel one. It has 3 marking. An I and h and a t o believe. I’m guessing t is tdc. When I put it on there online with the notch on the sight it’s not at tdc because I check with a pencil and when I turn the crank it goes a little higher.

I won’t be reusing the hg. I have another on the way. Also can you explain what rsc alignment process is? I basically just ignored the flywheel markings and found tdc myself.