Engine CSI

:blush: Nope, throttle was not open, will test again with it open!

All spark plugs were out and I was using two compression gauges to check, a new cheap one from Canadian Tire (bought it to get the adapter) and a Snap-on one I inherited from the in-laws. Both give roughly the same reading.

All wiring has been removed for testing and cleaning, so no worries about any ... accidents.

EDIT: Tested with throttle fully open ... no dice. The pressure still only hits about 30 psi. Pressing my finger over the spark plug hold while turning the shaft, I can feel the suction on the downstroke (but not much) and the pressure on the compression stroke (but not enough to push my finger off!) I can hear various woomping and hissing noises during the shaft rotation and a faint almost rubber sounding squeak. No grating, crunching or otherwise metallic sounds.

I suspect that the rings are old AND the exhaust valves are not closing (judging by the amount of carbon deposited in the exhaust ports, the seats are likely heavily fouled).

Any other ideas and suggestions as to what my next move should be? Open the block and examine the valves, cylinders and pistons?

Check my earlier link and verify cam timing. That can be done without any invasive disassembly. BUt doesn't sound good, so far, unfortunately.

Did it in fact run like that?

I've never seen it run. The guy whose yard I pulled it out of claimed that it ran when he left it there more than a year ago. Will check the cam timing and see if it's off.

Thanks!

Yeah, if you never heard it run, then I guess anything is possibly wrong.

If the motor is hosed, pretty much any chain-drive 550 motor will bolt in. Some may need some minor mounting parts/bolts that are different, but they'll all fit. ZX550 motors should go in real easy too.

Ok, checked the cam timing ... looks to be quite far off!

I set cylinder 1 to TDC (using the very high-tech pencil in the spark-plug hole method) and examined the cam lobes, chain and sprockets ... here's what I saw:

The left side of the engine. Notice that the inlet cam lobe is not horizontal, but pointing slightly downward. You can see the fouled piston head through the spark plug hole.


A side-one view from the right side of the engine. Not sure about the scratches on the inlet cam bracket ... kinda sketchy. Notice that the notch in the inlet cam is pointing way low.


View of the EX line on the exhaust sprocket (trying to get shot level with the casing) at TDC. Looks pretty good and level. Notice that the chain is 1 notch over, the EX line does not lie between links but instead in the middle of a link.


Now the inlet cam sprocket with cylinder 1 at TDC ... "Where is the Z5 line?" you ask. Way down below the level!


Rotating the shaft a bit more to level out the Z5 line (just so I can count pins on the cam chain). Notice that it also spans a link. The pin above the Z5 line is 44, the one below is 45 ... errr, that ain't right!


For interest, the view of the exhaust sprocket when the inlet has Z5 level.



Sooo ... can this cam timing issue account for the super low compression? Is this normal wear/stretching of the cam chain ... or did someone botch the cam timing?

Thanks

Use the timing mark on the ignition advancer to be sure your not a little off on the TDC for 1 and 4.

Also, it appears you have the length of chain between the cams tight. IT should have slack. That will rotate the intake cam forward where it will be closer to Z/5. However, if you are counting the pins correctly, then the intake is one tooth off.

The ex line does tend to be just above the head deck since the cam chain likely has a little stretch. Yours is not off by a full tooth, though, so it is set about as close as can be. You should only rotate the engine forward when timing the cams to make sure the chain is tight in the right place.



The z/5 mark is only level when the valve cover is in place, so there is no way to see it unless you make a jig. (It pushes down on the chain. This is also the reason why you have to release camchain tension before installing the valve cover.)

So if intake is retarded by one tooth, what happens? The gpz's had higher compression, but I don't see how a 1-tooth retarded intake cam could have to worry about piston to valve clearance, or valve to valve clearance, so you should be ok there. It seems like it would reduce compression test numbers since the intake valve would be open longer during the compression stroke such that the compression would leak out of the intake valve, but by that much? Seems like too much.

Yup, the chain is extremely taught between the two sprockets. How would I loosen it to give the required slack without adjusting it forward a tooth or so on the inlet cam sprocket?

I mean, the cam sprockets can't moved fore or aft, so the only way to get slack between them is by adjusting the amount of chain between them, not?

extremely taught between the two sprockets.

Remove and reset the cam chain tensioner

You have the complete procedure in the FSM.

/!\ Be careful! /!\

Be sure you have slack (reset tensioner) before putting the valve cover or you will damage the cam chain guides!

HTH,
laurent

Archiddeon wrote: Yup, the chain is extremely taught between the two sprockets. How would I loosen it to give the required slack without adjusting it forward a tooth or so on the inlet cam sprocket?

I mean, the cam sprockets can't moved fore or aft, so the only way to get slack between them is by adjusting the amount of chain between them, not?

First, you will have to relase the camchain tension if not already. Just remove the big cap (17mm?) and pull out the cross wedge.

Then, what I mean is, you have to push down on the chain between the two sprockets to make it look similar to the drawing. You can't judge intake cam position without the valve cover in place. You can only count links from ex to Z/5. But if you want to know what it will look similar to when the cover is on, then you just push down on the chain.

Since you've already counted the links, and they are off by one on the intake, you will have to walk the sprocket. I'm not sure if removing the tensioner completely will do it or not, but I thought you were going to replace shims, so the cams will eventually have to come off anyway.

I do it by removing the sprockets (the bolts are loctited on) and sliding the sprockets off the bosses which allow the chain to slacken. This way I don't remove the tensioner, (but you still have to remove cap and crosswedge). Then you can walk the sprocket on the chain to move it by a tooth. There are many ways to do it, and experience will dictate what method you like.

Just remember to get all of the oil out of the cam cap bolt holes. Get a very light torque wrench. Other tools you will likely want is a 10mm nut driver. Use a rag or shop vac to catch the loctite crumbs.

The main thing to lookout for is the cams will want to bind coing out and going in. Loosen and tighten the cam caps very very evenly and by single turn increments. If you do it right, they should never get bound.

The general procedure is in the manual.

You guys are awesome

Thanks for the heads up about the chain tension! I removed the tensioner rod to slacken the chain ... must remember to put it back at some stage Had a quick look at the chain guide and it seems pretty good. I can see faint grooves, but can't even feel them with my fingernail, so they're pretty shallow.

Turning the shaft now (with the tensioner rod removed), the chain goes through periods where it is quite slack (hangs between the sprockets) and others when it is somewhat taught (nothing like it was, but there is only about 1/2" up-down play). Is this variation normal?

Will probably set the cam chain when I shim the valves, as you suggest loudhvx

Do you think the piston rings need replacing? The compression increased when I PB Blasted into the cylinders. If so, should I do all the cam timing and valve shimming now, or after sorting out the pistons?

Turning the shaft now (with the tensioner rod removed), the chain goes through periods where it is quite slack (hangs between the sprockets) and others when it is somewhat taught (nothing like it was, but there is only about 1/2" up-down play). Is this variation normal?

Yes it is normal. Cam chain get slacked when valve are released and then tensioned shortly after when valve are being compressed!

No worries!

You could do valve shimming right now because you will need to do this anyway... and if it fix your compression readings back to normal then this will save you a piston rings job

laurent

Yes it's normal for the chain to jump around when the tension is off. Make sure you put tension on the chain by pressing down on the top when you rotate the engine. When the chain jumps around with no tension, that's when it can skip a tooth.

Only turn the crank forward, not backward, and slowly.