Topic: cam chain guide play

[yitzac1990]

Hello all, so i was having a serious rattle on my 1978 cb750K, and finally turned to removing the engine and taking the valve cover off.  The noise almost sounded like a loud knock or misfire, but it was intermittent.  Sometimes at low idle, it wouldn't be there at all, and sometimes after revving up, with RPM coming down, it would go away.  sounded like it was coming from around the center of the engine, so some friends and I think it is timing chain problems.  Here is a video of the play I have in the front timing chain guide:

is that amount of play normal?  or is it time to do a full timing kit replacement?  would this be causing a loud rattle in the engine when running?  Or is it something else?

Going back a little, i bought this bike as a project to fix up.  I got it running, took it up and down my street multiple times to test various things and the engine sounded okay, minus needing some carb tuning/adjustment.  when I finally took it "on the road" for real, it started making the noise after about a mile.  since then it has pretty much been parked in my garage.  the bike has about 26k miles on it.

[flybox1]

Its hard to tell what is actually moving. 
Is the sprocket on the cam actually loose?

[yitzac1990]

yeah I tried my best to capture what I was looking at....the sprocket on the cam is fine, and the whole top end seems fine.  no signs of anything abnormal, all valve clearances are okay.  I was mainly looking at that lower timing chain guide PIN at the bottom, as well as the guide itself.  i come from the world of cars, never really done any engine work on a bike, but I do know that guides on a car are not supposed to be loose.

[flybox1]

We cant see if your tensioner unit is fully engaged, or stuck in its place, which would keep the rollers from maintaining chain tension.
Set your motor to 15deg past TDC.
Remove the three screws that hold the cam chain tensioner to the rear of the cylinders, and slide out the unit.
Release the lock nut and bolt.  Pull out the plunger and spring.
Look at the flat of the plunger stem, and be sure it is smooth.  Any indents from the lock bolt might prevent the plunger from engaging as it should.  (the tip of the lock nut wants to find the intention it made.)
If its all good, clean and lube the plunger stem, and reinsert it into the unit over the spring, and lock it into place with the bolt in a compressed position.
Once its remounted to the cyls, release the lock bolt so the plunger slides forward, engaging the rollers against the chain.  Lock it in place.
Check for the same chain play.

[yitzac1990]

yeah i already had removed the tensioner and took it apart, inspected it all, actually lightly sanded off all the old grime, lubed it, and put it all back together and adjusted it correctly (15* ATDC, etc).  so i am like 99% sure that is good.

[flybox1]

Does the play of the chain change if you manually press the tensioner adjuster end with something?

[yitzac1990]

I didnt look at the play while holding in the tensioner end, but i did stick a screwdriver into the back of the tensioner, loosened the adjusting screw, and put some pressure on the tensioner, then tightened it up again.  and that was before taking that video.

[flybox1]

Adding more tension than what the plunger/spring can provide will certainly wear rollers and stretches chains faster than normal.

[yitzac1990]

i didnt run the engine like that, i only did it with the engine off the frame while i was doing this.  im just saying i didnt push on the plunger WHILE checking the slack in the front side of the chain.

[flybox1]

Did you attempt a complete tuneup, proper carb cleaning, and vacuum sync before the bike was apart?

[yitzac1990]

i did do a complete rebuild on the carbs and bench sync, but then this noise started before I could have it vacuum synced.

new spark plugs
new coils/wires
new plug boots
pod filters
4-1 exhaust
upgraded mains/pilots for the filters/exhaust

[flybox1]

A vac sync surprisingly quiets many noises...

[yitzac1990]

well I went ahead and ordered a whole new timing kit with heavy duty chain while i have the engine out of the frame and whatnot.  Once I put it back together, ill have it vacuum synced ASAP.  Will try to report back as soon as I figure it out!

[flybox1]

What kit and where did you order it from.  Big thread here about poor aftermarket kits w rollers tha t disintegrate within a few thou miles......Honda brand only here.

[yitzac1990]

the chain is the heavy duty Tsubaki chain from vintagecb750.com, and the roller, tensioner, and guide and OEM honda that I ordered off ebay.  also got a new lower guide pin from vintagecb750.

[yitzac1990]

I am at the point where my rocker arms are disassembled and out of the head, and the cam is just sitting in the cam channels (cam caps removed).  the cam sprocket is loose, tensioner is out, etc.  however, following the Honda shop manual, it says to just take the chain off the cam sprocket, remove the cam and sprocket, then continue removing the cylinder.  but i don't have enough slack in my chain to get it over the sprocket...is this the point where I use the chain breaker, and just break the chain?  if I do that, do I need to keep the chain suspended so it doesnt fall off the crank?  or will it be safe to leave loose, and it wont come off the crank?  I want to be able to do the "attach-and-pull-through" method for my new chain.

Im also replacing the guide, guide pin, rollers, guide rubber bushings, and piston rings while im at it, so thats why I need to take the cylinders off as well...

P.S. how do I make sure the timing is set correctly?  I followed the shop manual and put the crank at the "T" mark for 1-4 cylinders, and made sure the cam timing mark was horizontal and the notch was vertical.

[turkey4me]

If I'm following your progress correctly you should have plenty of slack in the cam chain to lift it off the loose sprocket without breaking the chain.  If you have to break the chain to remove it, something is wrong.  It's a bit of a puzzle but don't force it. 

[madmtnmotors]

Having two threads on the same topic makes it difficult to follow, and increases the odds of receiving conflicting information. As stated in your other request for information:

I am at the point where my rocker arms are disassembled and out of the head, and the cam is just sitting in the cam channels (cam caps removed).  the cam sprocket is loose, tensioner is loose, etc.  however, following the Honda shop manual, it says to just take the chain off the cam sprocket, remove the cam and sprocket, then continue removing the cylinder.  but i dont have enough slack in my chain to get it over the sprocket...is this the point where I use the chain breaker, and just break the chain?

NO! 

Remove the two bolts holding the sprocket to the cam, then slip the cam sprocket off the cam. Now you have the slack to lift the chain off the sprocket. Lift it to the side that the cam flange is on so the chain lands between the sprocket and the flange on the cam. Lift the cam and start moving towards the #1 cylinder while gradually nudging the sprocket and chain off the other end at the same time. Just take your time.

EZPZ 

[flybox1]

^+1
Gotta slide the sprocket/chain off the cam, first.  This will give you the space to lilft the chain of the sprocket.
Then suspend the sprocket and chain while you wiggle the sprocket out toward the cyl #1 side.

[yitzac1990]

hmm, ill have to take another look at it, but i am pretty sure there isn't even enough slack to slip the cam out of the sprocket...i wonder whats going on?!

[madmtnmotors]

hmm, ill have to take another look at it, but i am pretty sure there isn't even enough slack to slip the cam out of the sprocket...i wonder whats going on?!

Leave the cam in it's cradles, and slide the sprocket off the cam. You are not "slipping the cam out of the sprocket", you are slipping the sprocket off the cam. The cam chain tunnel is wide enough to permit this. I've done it many times, as have many members here. Once the sprocket is free from the shoulder of the cam the sprocket will drop just enough to free the chain as I described. Again, do not lift the cam until the sprocket is freed from the cam and the chain is freed from the sprocket.

[yitzac1990]

ahh much more clear, thank you!  so my other question is, once the chain is freed from the cam sprocket, do i need to hold it up so it doesn't drop off the crank sprocket?  or is the case designed so the cam chain physically cant fall out of place on the crank?

P.S. i see you're from Central FL...i'm originally from Melbourne

[madmtnmotors]

ahh much more clear, thank you!  so my other question is, once the chain is freed from the cam sprocket, do i need to hold it up so it doesn't drop off the crank sprocket?  or is the case designed so the cam chain physically cant fall out of place on the crank?

P.S. i see you're from Central FL...i'm originally from Melbourne

I usually tie a 3' or 4' nylon string to the chain to aid in retrieval. I have dropped the chain into the tunnel without any ill effects as far as alignment with the crank sprocket.

I just helped a friend move into a new house in Melbourne the weekend before Matthew came along. Boy, was he pissed! Fortunately we dodged a bullet and the affects were minimal, since the storm drifted just a little further offshore from us than predicted. Whew! Summers are pretty brutal here, so a more temperate climate may be in my future... 

[yitzac1990]

awesome I appreciate the info, you are a huge help.  I am used to doing timing on car engines, where you dont have to completely disassemble the engine lol, mainly nissan and chevy.

My mom still lives in Melbourne and wound up evacuating for the storm, but no real damage....i wish I was there for the storm, I totally would have stayed!  I miss hurricanes!

[madmtnmotors]

I miss hurricanes!

You ain't right...