Engine slapping noise

Working with a 78 400. I know this is nearly impossible to diagnose over the internet but maybe I can get pointed in the right direction. Loud knocking, more like a slapping noise sounds like its coming from my top end. It only happens when the engine is hot and when I give it throttle. Valve clearances are to spec. Took the head off last night and the top of the two intake valves look like they have taken a slight beating. the exhaust valves look ok. My right piston has a tad bit of play in the bore but I think thats normal. I dont know where to start really. Could this be a rod or bearing problem? A while back I drained the oil on this thing and It had some shiny bits in the filter. Any help?
Thanks

The manual sais it could be a stuck valve in the valve guide or something so I guess I can start there and see if that does anything.

A while back I drained the oil on this thing and It had some shiny bits in the filter.

That is a bad omen. I don't think sticky valves are the problem, a compression test and intake vacuum check would diagnose this further.

Piston slap would usually be worst when cold as the ally pistons expand...(a lot of new cars are bad for this as they use low friction slipper pistons with thin rings)

More noise when motor is loaded I'm thinking bottom end bearings, usually knock more than a slap. When i took main bearings out on a car it felt like driving over marbles, it died fast within a few miles, conveniently around the corner from a scrapyard.

The more you run it, the worse it's going to be.
steve

This is my only running bike I need something to ride!!! Oh well, Ill practice on that scrap motor first before I start this one

Did you check your cam chain tension ? a loose cam chain can make a slapping sound
Pete

Took the head off last night and the top of the two intake valves look like they have taken a slight beating.

Just re-read you original post, was the valve timing marks and top run links count correct when you took it apart? You might be needing the 'scrap' engine for parts here. Pics would be good.

a loose cam chain can make a slapping sound
Pete

Loose camchains have a sort of 'bunch of keys' tinkle, more than a slap, most apparent at about 4k on the 550's. Definitely worth checking though, it is a bit difficult diagnosing this remotely.

pete greek1 wrote: Did you check your cam chain tension ? a loose cam chain can make a slapping sound
Pete

Yep. Had to adjust it. Statrted it up and took it for a ride but noise was still there...And its a loud knock so It isnt the tension

Tyrell Corp wrote: Took the head off last night and the top of the two intake valves look like they have taken a slight beating.

Just re-read you original post, was the valve timing marks and top run links count correct when you took it apart? You might be needing the 'scrap' engine for parts here. Pics would be good.


Everything was correct to my knowledge...I do everything by the book. I can get pics. What would you like pics of?

Just interested in the inlet valves, this 'taken a slight beating' comment...do you think there has been piston/valve contact? Generally these motors have quite generous clearances when stock, hence they take quite a lot of abuse.

If the big end end bearing(s) is/are badly stuffed, you'll know as soon as you get the block off.

If the right hand bore has more clearance than the other, that could be a problem. Was the bore scored or any visible damage? Was it smoking at all? Check out my 'thar she blows' 550 thread, i had something similar...top end rattle and finally belching white smoke - it got much worse within a few hundred miles.

Bad lighting but best I could do. Bores are smooth , no scoring at all, but the right piston is scored pretty bad in that one spot as you can see. That's the only thing wrong with them. And the rod on the right cylinder has a ton of up and down play. Left one won't even budge. The build up on the valves is normal I believe. And that's about as far as I've gotten.

Tyrell Corp wrote:


If the right hand bore has more clearance than the other, that could be a problem. Was the bore scored or any visible damage? Was it smoking at all? .

Posted some pics. And this thing hasn't smoked one bit.