1977 XS400D engine knock?

[jcorney]

So my 1 year resto-mod project is done. It is running, riding, titled and registered for the first time since 1982. It seems to run fine, but I am getting a tapping or knocking sound when I give it a little throttle. It doesn't seem to be affecting the way the bike runs, but before I ride more than around the block, I would like to fix this issue. I rebuilt this motor myself. It is has the bottom end and pistons from a newer XS400 and the original cylinders and top end. When I first heard it, I checked my valve clearances. One was a little off, but barely. It sound almost like the rockers are bouncing, if that makes any sense. Here is a video of it. I would love to get your opinions.....

 

[drewpy]

are the carbs balanced?

there is a definite delay in one cylinder after you shut off the throttle

 

[16VGTIDave]

A couple thoughts:

- restricted oil flow to one of the connecting rods?
- loose con rod bearing?
- lean mixture on one carb?

Dave

 

[jcorney]

Thanks for the input. I have not synced the carbs. I think I am going to take it to a guy who specializes in vintage bikes to check them out. Fine tuning carbs is an art that I have not mastered yet!

I thought it could be an oil issue, but I rode it around last night and if I applied the brakes with the bike still moving, in gear and without the clutch engaged, the knocking went away. When I let go of the brake, it came back. I assume I was creating some sort of vacuum or something?? Do you think it is some sort of pre or post ignition, or that one carb is too lean?? I guess the best thing to do would have the expert dial it in. I would think that if it were mechanical, meaning piston slap or a valve hitting the piston or a bad bearing that it would be consistant and not go away at idle or when I applied the brakes. Also, I would think I would have destroyed the motor when I rode it the 5 miles or so. Maybe not though.

 

[xschris]

The engine will act different under a load. When you rebuilt the engine did you replace the pistons and rings with new or did you use old ones? It does sound like there is play in the engine(pistons, bearings, cam chain play, rod....).

 

[jcorney]

I did not get new pistons and rings. I am sure that it is possible that the engine is sloppy. I guess that I will have the mechanic look at it and if it ends up needing the engine rebuilt again, well....... we shall see. I'm not sure if I want to dive into that again. I am hoping that it has a carb issue!!! fingers crossed!!

 

[16VGTIDave]

I thought it could be an oil issue, but I rode it around last night and if I applied the brakes with the bike still moving, in gear and without the clutch engaged, the knocking went away. When I let go of the brake, it came back.

Interesting how it responds to the oil sloshing to the front of the engine. Based on this, I really think that you have a problem with the crank, bearings, etc. It would be in your engine's best interest to open it up and verify that all is well before you possibly do serious damage. If you find nothing wrong, you are out some time and maybe some gaskets. Or you will find that one connecting rod isn't getting oil (or the bearings are shot) and you should be able to salvage it.

Peace of mind is cheaper than an engine...

Dave

 

[jcorney]

Interesting how it responds to the oil sloshing to the front of the engine. Based on this, I really think that you have a problem with the crank, bearings, etc. It would be in your engine's best interest to open it up and verify that all is well before you possibly do serious damage. If you find nothing wrong, you are out some time and maybe some gaskets. Or you will find that one connecting rod isn't getting oil (or the bearings are shot) and you should be able to salvage it.

Peace of mind is cheaper than an engine...

Dave

The noise to me seems to be coming from the cam cover on the right side, but I know noise can travel, so who knows. Also, when the noise went away under braking, it was in gear without the clutch engaged. If I engaged the clutch while braking, I would still hear the noise. So I do not think it has to do with the oil sloshing forward.

In any case, I agree that there is no point in spending a year on a bike just to blow the engine in a day! I will be figuring this out before I run it again. I actually have an additional engine. I don't have a head for it, but if I need some parts (not bearings obviously) I could take it from that motor.

 

[Scorpio1963]

Get one those mechanic stethascopes and put it on your engine near where you think the noise is coming from.That will tell you alot if its a bearing or something else.I know by the sound Im hearing something doesnt seem right.

 

[jcorney]

So after further investigation, the noise seemed to be coming from under the side cover on the left side (where the starter is) I took the cover off and have found the source of the noise. The crank seems to have a little play. If I push and pull on the crank it moves slightly. It does not seem to have play if I move it side to side though. I looked at the disasembled 2nd motor I have and I can't seem to figure out how the crank would not have play, in and out like that. So now I am at a loss about what to do....

 

[xschris]

How many miles where on the lower end? Sounds like you need to replace the crank bearings or the crank has itself has issues

 

[Scorpio1963]

Is it the original engine from your bike and was it knocking before you rebuilt the engine?Your crankshaft should not move side to side or up and down.The whining noise that the engine makes would have me concerned also.

 

[jcorney]

The bottom end is from a different motor. Not idea what the miles are. The bottom case, crank, gears and pistons are from that different motor, everything else is from the original motor which has 5500 miles on it. The original motor was sitting for 30 years so all the oil turned to a soild and my original bottom end is sitting in the garage. I'm sure it could be cleaned and parts could be used. I took it to a local guy who specializes in vintage bikes. He did not hear anything else that sounded bad except for the knock. I was thinking that I could pick up this:
http://inlandempire.craigslist.org/for/3475840449.html and see if I could start again with a different motor. This one has a set of carbs too. Seems worth the buy regardless!

I will say that I am getting discouraged and the thought has crossed my mind to sell or trade it for something!

 

[jcorney]

Is it the original engine from your bike and was it knocking before you rebuilt the engine?Your crankshaft should not move side to side or up and down.The whining noise that the engine makes would have me concerned also.

The motor was seized when I got it. Never heard it run.

 

[xschris]

That's a good price for the engine, I would tell him $75 and get it!!

 

[Scorpio1963]

Well it is after all Pitmas time so he might take $75 for it but then again he might be one of those guys I dont realy need to sell it that bad I`l $90

 

[16VGTIDave]

So after further investigation, the noise seemed to be coming from under the side cover on the left side (where the starter is) I took the cover off and have found the source of the noise. The crank seems to have a little play...

Well, The up side is you found where the problem is and can now address the cause.

Dave

 

[Scorpio1963]

Given that fact the lower end came from another engine and you are having problems Im speculating that something didnt match up when did the rebuild.If you got another engine and you want to ride put in.Work on the other engine and figure out what the problem is.