GPZ750 - how tight should the cam chain be?

Hi. I am in the process of reassembling 1983 GPZ750 engine after replacing big end bearings. After I had installed the cams I cleaned the manual cam chain tensioner...it was worn and stuck but after some tidying up is now working good. I have not used this type of tensioner before so I just installed the tensioner with the adjusting bolt completely backed off, then once installed I started to wind in the adjusting screw. I could see the tension increasing on the cam chain as it was tightening between the cams but wasn't sure how tight it should be. I turned the engine over a few times and it all seems good but I am concerned I may have too much tension...but don't want to back it off too much... Does anyone know how much slack there should be in the chain?
Cheers

Brian

You should put your cam cover on first.
Check the cam timing marks.

Get your timing marks aligned, IN EX and the correct number of links between.
The lines should be level with the cam cover gasket face...unless your head has been skimmed. Then push a tool into the tensioner holes and turn it over a few times, the idea is to bring all the slack onto the tensioner side.

You'll see the IN is just a bit below the gasket face, if you indent the top run just a bit so it isn't stretched tight the IN will line up -that is what the top run of the camchain guide does.

So when the top run is tight, the IN will be slightly retarded, when the cam cover is tightened down it will put a tiny bit of slack in there, just enough to turn the IN cam by a few degrees for the timing marks to line up. Just to be sure I then turn it over a couple more times with a tool in the tensioner hole then refit the tensioner.

The 'auto' tensioners can stick, so cleaning and greasing with moly grease, also check the cross wedges for wear. There are manaul tensioners you can fit instead.

So, how much slack? just enough to make the IN line up, the top run on the tensioner will make this as the camcover is tightened down. Most important is that the timing marks line up and all the slack is on the tensioner side.

On the ZX750A1 motor you CAN NOT set the chain with the cover off
as there is a chain slider in it. I cut a spare cover and made a cam timing tool.

Unless you are dialing-in cams on slotted timing gears, a timing tool is unnecessary. Just refitting the cam cover, turn over a few times and then lifting it again will confirm timing marks -if you must. The top run indent is only a few mm. The IN cam will move by a few degrees as the top run is indented.

Hi. Thanks very much to the valuable contributions and information provided by members. I really appreciate it as where I live I do not have access to anyone who can help. Cheers Brian

You're welcome. Was it just the big ends or the main bearings too? these motors are generally very durable.

It has been a comedy of errors really. I recently built the bike up from an old GPZ750, the oil cooler was damaged so I removed it and blanked off the oil cooler outlet in the sump which allows the oil to circulate through the cooler... but I failed to drill out the plug between the oil galleries at the oil cooler outlet which caused the engine to be starved of oil and chewed up #1 big end. I only recently finished the build and went for a ride...when I heard/felt the engine starting to tighten I clutched it and shut down immediately so the damage appears to have been limited to the #1 big end. I pulled the engine to bits and everything was pretty close to spec so I cleaned up the crank (sprayed oven cleaner on #1 crank big end journal which ate up the alloy bearing deposit, but didn't hurt the crank... then polished up the journal and replaced the bearing shells) I have had a great time going through the engine. When I got to the CCT it confused me because it appeared to be a standard auto one but the previous owner must have modified the tensioner by drilling the end cap and installing a bolt to over-ride the cross spring on the cross section of the tensioner, so I am now treating the tensioner as having manual adjustment...hence the post about setting the right tension. Once I finish engine assembly I will give it a run and if the compression is okay I will probably go through it again and install a new manual CCT. I was going to install another primary drive chain whilst I had the crank out and found a used one for sale in the US for about $10.00 but the postage to Australia was $80.00 so I gave it a miss.. Sorry for waffling...Cheers Brian

Hi. Been a bit unwell so just got back on deck. I have had three goes at setting up the cams but can't get her to run properly. Took her for a short ride yesterday but no changes ... still running like a hairy goat.
I have changed around so many bits I ended up walking away from it last night...but we all know what it's like when we have a machine that you can't master...you have to keep at it until you win!!
Main things to consider are:
engine runs on 3 cyl and is back firing through carbies
not burning oil
# 2 will not fire. It's getting fuel, air, compression and spark but I suspect it's not getting them in the right sequence...
checked and re checked cam timing as per the manual and your suggestions and all seems okay
when cranking it kicks back and some times sounds like it is struggling with excessive compression - bit like when an engine has hydraulic lock up, but no noises like valves hitting pistons etc. maybe unburnt fuel in #2 increasing compression?
coils and plugs have been swapped around a few times during the process.
coil for 1 & 4 on the right hand side with the black wire connected to the positive and red wire connected to the negative.
coil for 2 & 3 on left side with green wire connected to positive and red wire to negative
clean fuel and it appears carbies are working okay.
the engine was running well just before it seized the bearing - easy to start etc
I have sorted out the oil issue and the oil now flows well
when I pulled it down, I noted the pistons are 68mm so it appears to have been re-bored
when the cam timing marks line up and are bolted down, they sit just below the cam cover surface and the 0 link is below the surface. link 45-46 is on the IN mark
chain tensioner seems sorted and when the engine runs it sounds good in terms of chain noises etc

Any thoughts or comments would be welcomed and appreciated.

Cheers

Brian

Top run is tight, any slack gets taken up on the tensioner side. Video clip shows GPz750R1 engine cranking.

Your IN valve timing mark being under the surface could be either incorrect valve timing, or the head having been skimmed. Timing marks on inlet dead flush with surface, EX just a few degrees out until you indent the tensioner top run. (The top run camchain guide indents the top run very slightly when the cover is bolted down)

Try swapping 2 and 3 coil plug leads, if the problem transfers to the other pot then assume ignition, otherwise likely fueling - your hydraulic lock is probably a float valve for that cylinder worn or stuck.

You shouldn't be turning it over without the valve cover on. Bent valves can be the result. Follow the procedures in your manual.
Steve

No experience here with the GPZ750...
Doesn't that cam cover have the tensioner bar in it to take up cam chain slack?
If yes, I can't imagine what the cam timing is with the chain run tight between the cam sprockets, as that AVI file shows.
Seeing how close the intake valve runs to the exhaust valve in overlap, I'd be surprised if there were not bent valves.