Fitting exhaust cam chain

[Chris in Dorset England]

My engine rebuild has come to an abrupt halt. The problem is fitting the exhaust cam chain and sprocket to the cam. The sprocket fits on to the shoulder on the cam, without the chain, the chain fits on the sprocket when the sprocket is NOT on the shoulder. However with the chain on the sprocket it will not fit on to the cam shoulder. It's almost as if the chain is too short. I have checked that the chain is seated on the crank correctly, not easy to see though. By sheer brute force I did manage to get the sprocket on to its shoulder but the chain seemed excessively tight and anyway the punch marks were way out of line and the sprocket was jammed, so I had to push it off again. The timing marks on the ATU were correctly aligned and # 1 cylinder cam lobes pointing at the plugs as per Honda Manual. All tensioners have been back off and locked. I'm at my wits end with this, I really do not wish to strip the engine down again. Any suggestions anybody, please

 

[amc49]

Everybody has fits with it. You have to just finagle with it to get it on. Two other guys here of late with the same issue. Brand new chain and sprockets with little wear and expect it to be hard to get on.

Haven't done anything like a 750 chain being used on a 900 or larger right? That would be too short a chain. The 900+ engines use longer cylinder blocks.

A VERY few early 750 had a slightly different size pilot on the sprocket, mixing wrong parts will have the sprocket not go on the cam. You say the sprocket does fit on the cam though.

 

[Chris in Dorset England]

Thanks for the reply. The sprocket does fit on the cam, (it's a close running fit) but without the chain! Not much use like that I have two ideas, neither of which I'm keen on: split the chain, add some links, chain might snap, grind off some of the shoulder to reduce its diameter, sprocket loose, rattles about.
It's winter here again, snow and cold wind (a present from Putin perhaps ) I will wait till the spring comes back and mean time think about what to do. PS my bike is 1982. PPS Got chain from David Silver, ordered by part number if its the wrong one they had better look out!

 

[Wez_]

I have two ideas, neither of which I'm keen on: split the chain, add some links, chain might snap, grind off some of the shoulder to reduce its diameter, sprocket loose, rattles about.

Deep breathes bruh...deep breathes....please don't give any of these ideas anymore thought

It helps when you install the cam caps to lower the cam/sprocket assembly about 5mm clearance (a lot of clearance!). Also, I took a set of Vice Grips and outfitted them with heavy duty tape to protect the tensioner. Use this "tool" to grab the tip of the chain tensioner with a kung-fu grip (nice and tight to do what you need to do) make it so the vice grips can barely close the jaw. Now wrap your arms around the motor, assuming its on a bench, and give the motor a big hug, maybe even a kiss. But really, while like this, grab the vice grips with one hand, and with the other loosen the tensioner lock nut. Now while hugging the motor, pull up with all your might on the tensioner and lock it in place. You can also use a pry-bar under the vice grips if they are tight enough and squeeze every bit of clearance out of the tensioner as possible.

Keep breathing...

torque down the cam/caps, install the sprocket on the cam shoulder, align the dots. and install the chain. Note the chain will only go on what I am calling 2/3s the way. The rest of the way will require some "stretching" of the chain. Get creative, use those pry bars and pliers that are collecting dust in your tool box, but there's no pretty answer for the install. The last bit of slack will require you to eat some spinach ahead of time.

 

[Chris in Dorset England]

Deep breathes bruh...deep breathes....please don't give any of these ideas anymore thought

It helps when you install the cam caps to lower the cam/sprocket assembly about 5mm clearance (a lot of clearance!). Also, I took a set of Vice Grips and outfitted them with heavy duty tape to protect the tensioner. Use this "tool" to grab the tip of the chain tensioner with a kung-fu grip (nice and tight to do what you need to do) make it so the vice grips can barely close the jaw. Now wrap your arms around the motor, assuming its on a bench, and give the motor a big hug, maybe even a kiss. But really, while like this, grab the vice grips with one hand, and with the other loosen the tensioner lock nut. Now while hugging the motor, pull up with all your might on the tensioner and lock it in place. You can also use a pry-bar under the vice grips if they are tight enough and squeeze every bit of clearance out of the tensioner as possible.

Keep breathing...

torque down the cam/caps, install the sprocket on the cam shoulder, align the dots. and install the chain. Note the chain will only go on what I am calling 2/3s the way. The rest of the way will require some "stretching" of the chain. Get creative, use those pry bars and pliers that are collecting dust in your tool box, but there's no pretty answer for the install. The last bit of slack will require you to eat some spinach ahead of time.

Thanks for the detailed advice, I did not carry my ideas any further so no worries there. I have devised a method for getting the chain and sprocket on the shoulder, it's repeatable not a 1 off. I will take some photos and post them later.

 

[Chris in Dorset England]

The exhaust chain is now on there is however a new problem Having fitted the inlet cam and with all timing marks in the correct places on turning the crankshaft the inlet chain tightens up, with further turning of the crank there is a click and the chain goes slack. The timing remains correct. It seems that with the engine running the chain would flap about. All chain guards are in place. Watching carefully the links appear to be sticking in the sprocket teeth and then popping out. It has been suggested that I have fitted the chain to run in the opposite direction as fitted before the strip down, would this cause the above problem? Thanks for any advice.

 

[dirtdigger]

Sounds to me like the tensioner isnt adjusted correctly. The chain is tight as it is turning against the force of opening a valve then when it goes over the lobe the valve spring force is trying to turn the cam. If there is slack in the chain it will snap when it takes up the tension on the slack side.

 

[Chris in Dorset England]

Sounds to me like the tensioner isnt adjusted correctly. The chain is tight as it is turning against the force of opening a valve then when it goes over the lobe the valve spring force is trying to turn the cam. If there is slack in the chain it will snap when it takes up the tension on the slack side.

Hi Thanks for the advice. I will check it out straight away. What you say makes sense. A broken chain is not something I want!

 

[amc49]

'It has been suggested that I have fitted the chain to run in the opposite direction as fitted before the strip down, would this cause the above problem?'

Uh, no. The wear is different entering and rolling back off the sprocket teeth. The industry norm is to mark the chain to have it go back in turning the same way. Cars do it the same way as well.

Pay attention to post #7, the chains loosen and tighten depending on which valve springs load them and a few can even load backwards at certain points to try to loosen the chain until you rock engine over more to then pull the other way. To preclude that there is a certain position that Honda knows of as pretty much loaded in a neutral way and you set the chains at that point to remove the max looseness there. The service manuals have it in there IIRC, and likely in the early 'maintenance and adjustment' section. The SOHC is the same way.

I know that the early DOHC manuals said to set the chain tension while idling, that later was disapproved of and they went back to setting static and in a certain place.

 

[Chris in Dorset England]

'It has been suggested that I have fitted the chain to run in the opposite direction as fitted before the strip down, would this cause the above problem?'

Uh, no. The wear is different entering and rolling back off the sprocket teeth. The industry norm is to mark the chain to have it go back in turning the same way. Cars do it the same way as well.

Pay attention to post #7, the chains loosen and tighten depending on which valve springs load them and a few can even load backwards at certain points to try to loosen the chain until you rock engine over more to then pull the other way. To preclude that there is a certain position that Honda knows of as pretty much loaded in a neutral way and you set the chains at that point to remove the max looseness there. The service manuals have it in there IIRC, and likely in the early 'maintenance and adjustment' section. The SOHC is the same way.

I know that the early DOHC manuals said to set the chain tension while idling, that later was disapproved of and they went back to setting static and in a certain place.

Hi, Thanks again for your advice. I will go back a few steps to check if I have done something wrong. Excuse my ignorance, but what is IIRC? I think to avoid any problems with chain wear I will fit a new one. They are cheap enough and a lot less than having it break!

 

[Wez_]

Luckily the short intake camshaft is easier to install and remove. But if the chain has enough slack to skip on the sprocket, i would double check the dots on both cams. If nothing has changed, perform the chain tensioner adjustment as noted here and remove the slack. IIRC means if i remember correctly.

 

[Chris in Dorset England]

Ah! thanks for the IIRC! I couldn't work it out I will be sorting the chain tensioner out. Is there away of determining the direction of travel on the inlet chain from witness marks? Thanks again for your help.

 

[amc49]

'Is there away of determining the direction of travel on the inlet chain from witness marks?'

You'll play h-ll doing that one. The pins show it most but they are buried in the linkplates. Why one marks them quick at disassembly. Maybe sprocket will have enough tooth marking to suggest it, match to the chain.

 

[Chris in Dorset England]

Thanks, I will give it a try.

 

[Chris in Dorset England]

Sounds to me like the tensioner isnt adjusted correctly. The chain is tight as it is turning against the force of opening a valve then when it goes over the lobe the valve spring force is trying to turn the cam. If there is slack in the chain it will snap when it takes up the tension on the slack side.

You were correct about the tensioner being the cause, however it was the spring had slipped out its hole at one end . To get it back on I had to take the whole lot off again. To stop myself throwing the whole lot out of the window I have walked away from it for a few days. The production line workers who built these engines were masters of a black art.

 

[Wez_]

Very good idea bud. Be patient, and keep thinking about what's next. When you have it all planned out in your head, knock it out.

 

[amc49]

X3..............I know engines of all types forward and backward and I have to walk away at times as well. The time separate spent thinking only often produces a cure by the time I get back.

Don't get mad, get smarter.

 

[Chris in Dorset England]

Thanks gents. I am actually building a DOHC CB750 and it's looking good. Metallic black with gold wheels. Problem is I will never ride it Why? you ask, It's a 1/6 scale Tamiya Supersport model. Excellent kit and good therapy. Its my own colour scheme. Be nice if the full size engine went together as easily!

 

[amc49]

Got one as well as the unobtanium one............a CB1100R and an RS1000 as well. Mine I'm thinking are around 1/12th scale. Plastic model kits I credit with stoking my desire to learn how mechanical things worked, I used to build them in uncountable amounts when young and I began to gravitate toward any that had 'working features' of course I did not have the success I do today. I built the Revell Visible Ford Turbo four engine back in the early '80s, it still works perfectly today. I got plastic kits coming outta my ears.........

Just ran across a heck of a deal-Hobby Lobby ditching some kits at almost cost, got the old MPC recast 1/8th scale Honda SOHC 750 Daytona Roadracer. $40 kit for $12.

 

[Chris in Dorset England]

Got one as well as the unobtanium one............a CB1100R and an RS1000 as well. Mine I'm thinking are around 1/12th scale. Plastic model kits I credit with stoking my desire to learn how mechanical things worked, I used to build them in uncountable amounts when young and I began to gravitate toward any that had 'working features' of course I did not have the success I do today. I built the Revell Visible Ford Turbo four engine back in the early '80s, it still works perfectly today. I got plastic kits coming outta my ears.........

Just ran across a heck of a deal-Hobby Lobby ditching some kits at almost cost, got the old MPC recast 1/8th scale Honda SOHC 750 Daytona Roadracer. $40 kit for $12.

Nice one, problem here in the UK is postage from the U.S. and all the other taxes our wonderful government slap on