cam timing trouble with chain going slack after valves shut

I'm getting everything back together with the 615 kit in, and I timed my cams up the way the manual says, and the way I had last year (I made a post just to make sure aI was doing everything right back then).

When I rotate the crank, everything goes smoothly until a valve starts to open, and then BAM it slams shut, accelerating whichever cam it is, to the point that there is a tremendous amount of slack in the chain.

When it happens with the intake cam, the slack is obviously visible between the two cams. sometimes it jumps with such force and creates enough slack that the chain is knocked forward off of the exhaust sprocket!

As side noet, the first time that happened, I rotated the crank forward slightly without re-seating the chain, but of course it started to get tight, so I stopped. I don't think any of the valves would have been in the position to hit pistons, but it slightly concerns me.

Every time I bring the crank around twice, everything is in line though..

you need to install the tensioner before you start turning it over. When it's time to put the valve cover on, if the bike has a guide in the valve cover that presses on the chain, loosen the tensioner, install the cover, and then retension. If you turn it over without the tnesioner, it's gonna do just what you see.

-duck

hm, maybe it has something to do with the manual tensioner I installed eh?

The stock tensioner would always put tension on the chain coming up the rear to the intake cam. I would have to puuull the intake came back into place. I remeber it still sort of doing the 'tension and slack' thing though, but never as noticable.

I did try putting the valve cover on with a bolt in front and back, and tensioning up the tensioner. I could still hear it doing its thing every time a valve coulw slam shut. I guess that doesn't happen while running though, the chain has those cams zinging along so fast that they push the lifter and are off it before it slams shut

I guess I'm getting a bit frazzled, putting it all back together in two days after so many months in parts. Plus the head and block were resurfaced and I know that can affect cam timing. Plus it would be just my luck to bend a valve!

cams are not supposed to get pushed around by valve springs. well not so much as to be noticeable anyway. if you took a lot off the head and block and you've got a lot of miles and that's the original chain...

does it have much side to side slop? sure sign a drive chain is worn and should apply for camshaft chain as well. or you might measure against book spec.

Can get it tight with the valve cover off or do you run out of adjuster first? Original guides? Didn't forget to install?

It's got around 13-14 thousand miles on it, and it's probably the original chain.

I had both the block and head resurfaced as they had around .004" of warp. I was told that they took around 4-5 off the head, and I had APE do the block when they had it. Told them to take the minimum, and I dunno how much that was, but the piston outer edges (the lowest parts) were flush when at TDC, or at least appeared flush so I don't know that it was a hell of a lot.

I can turn the tensioner in without the valve cover and get rid of the slop, but it is pretty far in there.

I stuck my stock automatic tensioner back in there, and that pretty much fixed it. I have yet to see what is so great about these manual cam chain tensioners.. !

See my other post about kissing the valve into the piston? I cranked it over with the starter (automatic tensioner in place) and took compressions. 100-120 on all cylinders, so I guess I'm ok. Of couse that is cold on an engine with fresh rings, bores and fresh cut valves.

When you installed the cams, exh cam goes in first AFTER you pull all the slack out of the chain... then the intake cam. If you did that, then you didn't tension the chain properly as what you are describing sounds like slack. You CAN turn the bike over carefully without installing the tensioner to check cam timing but the chain will bunch and pop like described. To use that fancy APE tensioner, you need to know what a properly tensioned chain looks like... put your idler assembly on as well as the tensioner and tighten down the bolt so that the chain doesn't buckle up when you move the chain back and forth over the idler assembly... you can also try calling APE for their tips on how to use one of these tensioners. I think they are a poor idea for someone who doesn't have good feel for chain tension already but they may have some instructions to help guide you over tensioning the chain.

Personally, I never had a problem with the automatic tensioner. I'd jsut always heard that "manual tensioners are better" so I figured I'd pick one up while my block was out there anyway. Maybe later.

Yes, I made sure I checked and double checked that I had the slack out of the front of the chain before putting the exhaust cam in. Then I counted my pins and put the intake in, so everything should be the way its supposed to be.

I can turn the tensioner in untill it holds all the slack out of the chain. In fact I realized that and did that to check my valve clearances.

I guess I assumed I needed to have it backed out all the way, because, well I don't know. Obviously my stock tensioner puts a good bit (just not final tension I guess) on the chain with the cover off.

With the stock tensioner in, valve cover on and stock tensioner cap on, it turns over like it should, fairly smooth all the way around.


The manual tensioner says "Turn the engine over by hand, while turning the adjusting rod in until you feel that it makes contact with the moving chain, and then back it out a quarter turn and set the lock nut"

Yea.. try doing that shit in real life.

Does that bike have a cam chain guide up in the top of the valve cover? If so, I may have been speaking out of place as I think you have to have the cover on for the chain to be tensioned properly. What type tensioner do you have other than the APE? I can think of three types used in the 70s and early 80s...

Well this post slipped away..

But yes, there is a guide in the valve cover, and the valve cover being on plays a part.

The tensioner is a spring-loaded rod, with a wedge end on the rod inside the housing. After the valve cover is on, there is another small wedge that you stick in the side, install a small spring on, and then install a cap over. The spring-loaded rod can now move in as the guides wear or the chain stretches, but not back because of the spring-loaded wedge against the rod end wedge.