Calling Anyone Who Knows DOHC Motors!!

[pulmenti]

Hi!! I've made probably too many posts here asking for help on my '82 Maxim. It has the twin cam motor, and I'm having a lot of trouble finding any usable information / manuals / tutorials / people who know anything about it. I think a lot of my issues are coming from having set it up as if it's a SOHC. If anybody knows about these motors / has a manual they can share, or any advice they could give me, I would be infinitely grateful.
Pulmenti

 

[CaptChrome]

Scans of the manuals for both SOHC and DOHC models is on this site, right up at the top of the Garage forum. The post is pinned to the top and called
Yamaha XS400 Manuals.

 

[pulmenti]

Hi and thank you, I've checked out those manuals and have still ended up hitting brick walls ! I'm hoping for some kind of troubleshooting guide, or somewhere I can get some answers as to why this bike isn't running

 

[tstidham]

You may have to double check your cam timing using the instructions in the manual. Get it to TDC on cylinder 1 and make sure your marks are correct on the cam gears. That is if I recall correctly that you had a previous post about messing with the cam gears.

 

[pulmenti]

You may have to double check your cam timing using the instructions in the manual. Get it to TDC on cylinder 1 and make sure your marks are correct on the cam gears. That is if I recall correctly that you had a previous post about messing with the cam gears.

I'll double check this, but the main issue I've been having is the fact that the manual only ever refers to the intake cam, and never once refers to the exhaust cam when describing timing. It says to align the L mark with the line, and then to set "the" cam to have the dot align with the arrow on the clamp. It was guesswork to have the exhaust cam match that. Is the exhaust cam supposed to be set at the same time as the intake, or is there more to it?

 

[tstidham]

I just read through the DOHC cam timing and yes, the dots on both cams (1) should align with the arrows on the cam caps (2). However, they do have some pretty specific details on chain slack in differing spots and directions to turn the cams while assembling to ensure proper cam chain tension and the ability to install the gears and guides. For the DOHC, the cam chain tensioner is below the carbs, so that means you will always want to have the most tension on the chain towards the exhaust side of the engine, and all slack (when done assembling) of the chain on the intake side.

Do note though that there is an O mark on the edge of the cam flange (1 in the image) and what appears to be a hole in the face of the cam flange (unmarked in the image but 90 degrees clockwise of the O mark), so make sure you didn't align the hole with the cam cap arrow. Once you think you have it right, just snug up the cam gear bolts and rotate the whole engine over by hand 2 full crankshaft rotations, and realign the crank marks, then both cam marks should also be aligned. If they are not, you likely have something one (or more) tooth off, so just do your best to unbolt that cam gear, get enough slack to reposition the chain and snug it back up and do your rotation check again. This also may require removing/reinstalling the cam chain tensioner a few times as you get it all aligned. Tedious but worth it in the end. One other suggestion while doing this is every time you are removing/installing those cam gear bolts, stuff rags under and around the cam and gear and down the chain opening, then remove them when you have to rotate. It takes extra time, but if you drop the bolt down that hole while trying to remove or install, it'll take even longer to fish it back out. Slow and steady wins the race!

 

[tstidham]

Oh and I'll add that if your chain has some stretch in it, it's normal for the alignment marks to be off slightly towards the intake side of the engine some.

 

[pulmenti]

I just read through the DOHC cam timing and yes, the dots on both cams (1) should align with the arrows on the cam caps (2). However, they do have some pretty specific details on chain slack in differing spots and directions to turn the cams while assembling to ensure proper cam chain tension and the ability to install the gears and guides. For the DOHC, the cam chain tensioner is below the carbs, so that means you will always want to have the most tension on the chain towards the exhaust side of the engine, and all slack (when done assembling) of the chain on the intake side.

Do note though that there is an O mark on the edge of the cam flange (1 in the image) and what appears to be a hole in the face of the cam flange (unmarked in the image but 90 degrees clockwise of the O mark), so make sure you didn't align the hole with the cam cap arrow. Once you think you have it right, just snug up the cam gear bolts and rotate the whole engine over by hand 2 full crankshaft rotations, and realign the crank marks, then both cam marks should also be aligned. If they are not, you likely have something one (or more) tooth off, so just do your best to unbolt that cam gear, get enough slack to reposition the chain and snug it back up and do your rotation check again. This also may require removing/reinstalling the cam chain tensioner a few times as you get it all aligned. Tedious but worth it in the end. One other suggestion while doing this is every time you are removing/installing those cam gear bolts, stuff rags under and around the cam and gear and down the chain opening, then remove them when you have to rotate. It takes extra time, but if you drop the bolt down that hole while trying to remove or install, it'll take even longer to fish it back out. Slow and steady wins the race!

View attachment 38253

Thank you so much for this, I was having a really hard time with the manual. I know I didn't touch the cam gear bolts among other things I probably didn't pay attention to.