Timing Chain

[WaterMover77498]

I am preparing myself to repair my rear head. The intake valves are not sealing.

I have a spare motor that I was going to tear into so that I will be more comfortable when I tear into the motor on my bike. My biggest concern is not letting the timing chain slip off the teeth of the timing gear deep down in the engine. Often, this involves wedging something into the chain so it doesn't move when the head is removed.

My normal wooden wedge probably won't work because of clearance issues since the motor is still on the bike. I pulled the head of the spare engine to see if I could learn more about keeping the timing chain in place.

What I think I've learned is the chain stays up pretty much on its own. In fact, I haven't been able to get the chain to come off the timing gear on the spare engine when I've tried.

If there is something that keeps the chain up, that would be great, as it will make this job much easier. If anyone has experience showing that the chain can in fact slip off, that would be helpful information to keep me from getting complacent.

Thanks again!

[The Prophet of Doom]

So you've done a leakdown test and failed then?

You don't need to worry about the timing gear down below. I tied some fishing line to my chain to make it easier to fish back up through the head but no pieces of wooden wedge  or sky hooks needed.


When you re-install the cams, you rotate to suit.  With the tensioner loosened you can pull up on the chain and slip it over the cam sprockets, a link at a time, keeping the cams still while you find TDC on the crank.

[WaterMover77498]

Yes, I did a leakdown test. Attached is a picture of the tool I made for the test. It is basically my compression tester threaded insert with connections for a compressed air hose.

I poured engine oil in the intake side of the head so I could "see" the air leaking past the valves.

I live in a very humid environment. My hope is light rust is keeping then valves from sealing after the bike has been sitting for a long time, and something as simple as lapping will get me back to where I want to be. I'll keep everyone posted.

[Rikugun]

Not a perfect solution but is it worth a try to free up the valves with the head in place? A quick Google search on freeing stuck valves shows lots of results.

As part of head removal you have to remove the cams. There is probably little room to do this (due to the springs) but with the intake cam and buckets removed, could an aerosol penetrating oil be directed at the valve stem/guide interface? In between soakings find a way to lever the valve open and closed. Maybe by soaking and cycling the valves will free up.

If the compression goes up at all, subsequent running may improve valve sealing. If it doesn't and you end up having to R&R the head, you planned on doing it anyway. If it does work, you've saved some $ and labor by not having to R&R the head. Depending on your experience lots can go wrong with such an endeavor.

Either way it sounds like you've diagnosed the problem well and good luck with the repair.

[fiat-doctor]

It does look like you have found the problem.  However, you might find that running the bike for a while (even if it runs poorly at first) will "fix" the sealing without need to disassemble.  I have found that compression tests and leak down tests on a motor that has set for a long time often show problems that vanish after it's been run for a few hours.  If not, nothing lost.  Just my .02.  Steve

[motoracer8]

Don't worry about the cam drive chain. Remove the tensioner to give alittle more play. If the chain goes down the hole a piece of bent wire will fish it out. If you remove the sprockets from the cams it's easier to get the dots on the cams to line up perfectly once you find TDC on that cylinder. You can move the sprockets around the cam until you find the spot where TDC, the punch mark on the cam and the chain go together.  Keep the chain tight on the drive side. Once you have it back together turn the engine several times to make sure the crank and cams are in time. With alittle patience you can get the cam timing right on or very close even with worn cam chains.

Ken

[WaterMover77498]

Here is where I was going with timing chain questions. From experience with other duel overhead cam engines, I've seen the following work very well for resetting the valve timing with no guess work. The only prerequisite is to not let the chain come off the bottom of the bottom timing sprocket so the same number of links will be in place between the bottom sprocket and the marks I will mention below.

Do the following before releasing tension:
1. Make a mark with a paint crayon on the links above the two sprocket marks.
2. As a backup, count the number of links in between the two sprocket timing marks
3. As long as the chain doesn't come off the bottom timing sprocket, putting the marked links back on the sprocket at the timing marks will put the valve timing back right where it was.

This is why I was asking specifically about the possibility of the chain coming off the bottom timing sprocket. As several posters have said, it looks like there are plenty of ways to get the timing back if the chain falls. I was making a comment that I don't think the chain can come off the bottom of the sprocket, but I'm not sure what is keeping it from coming off.

Thanks again! I've been very impressed with these engines as I've torn into a couple.

[Rikugun]

The design of this engine may be that there isn't room for the chain to skip teeth at the crank when tension is released - I personally don't know. Having said that, the care required to not let the chain skip teeth and hoping the paint crayon marks don't get eradicated seems unnecessarily tedious. Most members who have done this type of work typically use the manual's procedure or some variant of it. The bottom line is use the procedure you are comfortable with but if you get in trouble and want help, most here will likely reference the factory procedure, crank and cam marks, etc.

Even if I have a manual for the engine I'm working on I'll still note the position of the various crank and cam sprocket marks prior to disassembly. There are free manuals for your bike on this site BTW. Counting chain pins between the sprockets can be helpful. DOHC engines with a slipper on the cam cover (Kawasaki used this a lot) need this reference. Also, on high mileage engines chain stretch can alter alignment of reference marks resulting in some head scratching upon reassembly so pin counts can be reassuring. Based on the mileage you reported and the robust nature of the HyVo chain, I'd think stretch shouldn't be an issue.

[The Prophet of Doom]

The bottom sprocket can slip. but it's irrelevant.


Set the crank to the TDC mark on the flywheel, then with the tensioner off, rotate the cams till they are aligned when you use your finger as a tensioner. 
Check they are still aligned with the tensioner in place.  Done. 


Repeat for the other cylinder with the other TDC mark. Valve activation should be a full rotation +-70degrees apart.


Double done


4 years ago I was a cam adjustment virgin, then I saw this most excellent post from Fuzzlewump.


Now I do cams and twingles like a boss

[WaterMover77498]

Just wanted to give everyone an update.

Without going into all the details, my bike is running as well as I've ever seen it run. I didn't end up pulling the head. I am taking out my need to crack open and improve an engine on a spare I got. All of the things that got me running were bits and pieces of everyone's suggestions. For that, I am very grateful.

Thanks to the one time previous owner of both of my Visions, I have a fuel tank that is pristine inside. That seems to have helped greatly after all the forum post.

Thanks again all! I've enjoyed putting some miles on the bike this weekend.

[Rikugun]

I'm glad you got it running well and especially without having to dismantle the engine.

[The Prophet of Doom]

Without going into all the details, my bike is running as well as I've ever seen it run. I didn't end up pulling the head.

I for one would be interested in the details.  It's a big jump from leaking intake valves to running as well as ever...

[WaterMover77498]

Here are the things that seemed to make a difference:

Leaking valves: as suggested by various posts, the valves sealed up after blowing some air from spark plug hole during leak down tests. Not very scientific, but I will take it right now. Compression is still pretty low on rear cylinder (110 PSI), but its running.

On the subject of synchronizing carbs, I could never get them to stay synchronized. I decided this had to change. I found a lot of play in the front carb lever that connects throttle to butterfly valve shaft. Replaced this. In the process of searching through my spare carbs for the best front carb butterfly valve shaft, I found that other spare carb sets (I have about six spares sets, some '82, some '83) had a brace between both carbs on the throttle cable side. Mine only had the brace on the chock cable side. What was even more strange was the hole that should have been threaded to hold the brace's fastner never had its threads cut. I tapped the hole with the correct threads, and installed the brace. Since then, there isn't the same level of play in carbs that would mess up synchronization.

Lastly, my rear pilot jet had "always" had most of its screwdriver slot "rounded off". It was hard to remove or install, but I never questioned its affect on how the carb functioned. I looked at my stack of spare pilot jets, and thought it was silly to keep working so hard to remove and install that jet when I was cleaning the carb. Other than that, I began to wonder if pushing the screwdriver so hard into the slot so it didn't slip might be damaging the jet's bore. Sure enough, there were fine brass shavings in the jet bore.

There are still probably plenty of things to do to the bike. I am just glad it runs and moves me around. It was getting hard to convince my wife that the two Visions that were given to me for free with stacks of parts were worth the space in the garage. Valve shims will be my next project for this bike. I want to start bringing my '83 back to life as well. Having a running bike gives me that much more confidence. Thanks again to all for the help.

[Rikugun]

Mine only had the brace on the chock cable side. What was even more strange was the hole that should have been threaded to hold the brace's fastner never had its threads cut. I tapped the hole with the correct threads, and installed the brace. Since then, there isn't the same level of play in carbs that would mess up synchronization.

I have a set with one brace. I've read on the forum it is an early example. Apparently some flexing occurs allowing sync to change. The fix was to add the second brace.

As far as the low compression goes, I'd check it again after several hundred miles and see if it improves. If so, you will probably need to check the sync again. Definetly check it after any valve shims are changed too.

Thanks for the update to your work. I think it's helpful for others in a similar place and gives confidence to continue working through the problems.

[WaterMover77498]

Thanks for the encouragement. I am hopeful my rear compression will improve. One of my biggest problems before was lots of fuel coming out of the rear secondary Venturi. I fear the hour or so I allowed this to go on with a super rich mixture stripped the cylinder or its natural oil coating. I am optimistic that it will come back.

Good luck to anyone else starting out with these bikes. It's been about 18 months. I pretty busy right now, so months went by without much going on, but I've never spent so much time to get to the point I am now with a project. I've been very impressed with the construction of the engine I have been taking apart, so I think the time will be well spent in the end.