XS 750 Valve "Hammering" Noise - Video!

[PancakeShake]

So I took the heads off the bike to check the pistons, and when I re-assembled the engine something changed within the intake valves.

When the engine is cranked, the intake valves make a very loud metal-on-metal hammering sound. When i took the cam cover off the engine, I noticed that the intake valves are snapping back to the closed position after being open rather than being smoothly closed with the cam like they should be.

Before the engine sounded fine, but after I put the cams back on, the spacing between the cam followers and the valves disappeared. The cam follower is always in contact with the valve as it rotates

I have never dealt with valves so any and all help here would be great, then manual hasnt proven very helpful for this one.

Thanks guys.

Here is a video of what im talking about.

http://www.youtube.com/watch?v=rw2vehcF3To&feature=youtu.be

 

[suddenlycalm]

Sounds to me like you're hitting the top of the pistons. Having just redone 1 of these Yamaha engines I realize that there are a lot of things that can be installed, or adjusted improperly.

 

[PancakeShake]

I can see the valve snapping back into place viciously rather than "floating" back into position like it should. The cam should produce a smooth motion and its not. Its just snapping back.

It might be the pistons tho, ill check right now...

 

[Sonreir]

I was getting the same symptoms after I put the rocker arms back in, incorrectly. I ended up bending a valve.

 

[suddenlycalm]

How did the cam chain gears line up when you reinstalled. I had a hell of a time getting the new master link to fit after my engine was torn down. It was such a perfect fit that i thought something was wrong. Just no extra clearance when the cam gears were indexed correctly.

 

[PancakeShake]

I never had to break the chain, took the cogs off and the cams slid out and the head came off w/o having to break it.

 

[PancakeShake]

So its not the valves hitting the cylinders. Its defiantly the valves snapping closed to fast causing the loud bang.

How do you do valve spacing / shimming? never dealt with valves before.

 

[suddenlycalm]

The valves on these are shim over bucket style valves. You need a special little tool to depress the bucket and remove the shim. The clearances are checked with feeler gauges, and compared to factory specs. Once the difference is found the measurements are cross referenced with a table of shim sizes. Once the correct size is chosen it gets inserted into the bucket and clearance checked again. It sounds way more complicated than it is. The Haynes and clymer manuals do a great job of explaining the process.

 

[rockcitycafe]

So I took the heads off the bike to check the pistons, and when I re-assembled the engine something changed within the intake valves.

When the engine is cranked, the intake valves make a very loud metal-on-metal hammering sound. When i took the cam cover off the engine, I noticed that the intake valves are snapping back to the closed position after being open rather than being smoothly closed with the cam like they should be.

Before the engine sounded fine, but after I put the cams back on, the spacing between the cam followers and the valves disappeared. The cam follower is always in contact with the valve as it rotates

I have never dealt with valves so any and all help here would be great, then manual hasnt proven very helpful for this one.

Thanks guys.

Here is a video of what im talking about.

http://www.youtube.com/watch?v=rw2vehcF3To&feature=youtu.be

that's what they do when they're bent, they stick open until the piston hits them, then they pop back up, it's because the stem is bent. stop turning it over before you do more damage to your guides, there's a chance the guides are save-able enough to just reinstall and reseat new valves.

 

[PancakeShake]

that's what they do when they're bent, they stick open until the piston hits them, then they pop back up, it's because the stem is bent. stop turning it over before you do more damage to your guides, there's a chance the guides are save-able enough to just reinstall and reseat new valves.

This.

I can totally see this being the reason. Ill have to buy some new valves.

Thanks

 

[PancakeShake]

Update.

Got the engine apart, re-assembled, and it sounds better. I think the cams werent fully indexed correctly.

Now the issue is we cant get it to start, the bike has plenty of spark but no boom. When I cranked it over, i was looking in the carb intakes and I can SEE the spark plug sparking. This is bad right? Cause the intake valve is open when the spark plug is sparking...you dont want that.

So, is the timing just WAY off, or could the cams be wrong? Im pretty sure we have the plugs in the correct spot too.

Any ideas guys?

 

[mydlyfkryzis]

Are these 180 degree or 360 degree engines?

360 degree engines usually have a waste spark...both cylinders fire at the same time.

The spark should not be seen through the intake valve though, just the exhaust. Sounds like your timing is off 180 degrees.

Maybe someone with the same bike can chime in here. However, getting the timing wrong after head work is common among the Honda 350/360 bunch.

 

[PancakeShake]

Are these 180 degree or 360 degree engines?

360 degree engines usually have a waste spark...both cylinders fire at the same time.

The spark should not be seen through the intake valve though, just the exhaust. Sounds like your timing is off 180 degrees.

Maybe someone with the same bike can chime in here. However, getting the timing wrong after head work is common among the Honda 350/360 bunch.

How do you go about fixing timing thats 180 off?

Because I thought that was the case, so I adjusted the cams. The cam index marks line up every 2 full engine rotations so I rotated the crank shaft 360 back to TDC, causing the cam index marks to be 180 degrees off, and adjusted the cams so they were indexed at that TDC mark. But when I cranked the engine over it was hammering on the valves so I just put it back to the way it was.