Primary chain guide: two or three bolts?

Just started to install the new chain guide, and it fits, but the new one has two bolt tabs while the old one had three (an additional one in the middle). Is that a problem?

 

Actually, just saw in Chacal's catalog that some OE guides had three tabs and the new ones have two. So, I guess it's fine.

Actually, it's not entirely fine. The new one leaves so little room between the last plastic block and the screw head that it's pretty much impossible to line the bolt up. It cross threaded, seized, and broke.

 

The latest version from Yamaha has only two bolts. Mine was the same. My vote is it’s fine as Yamaha must have had a good reason to make the change..

 

Basically, what I found is that it's not possible to get the original hex head bolt in place with the new guide. I will be using an Allen bolt instead, but I will first have to install a Helicoil in that hole, since the damaged threads won't take 7.2lb/ft of torque anymore.

Wasn't a fun spot to drill or to try to use an extractor. I'm glad I was able to get the remainder of the old bolt out.

 

OK. So, now it's drilled through, but I need to get some tap sockets because I can't reach a tap handle in there. What a pain.

Do the new guides use socket head bolts instead?

 

Hi mate, check out my rebuild video below. I used hex heads but socket heads will work too. I use Loctite on bolts inside the engine to be sure they can’t work loose..

 

The original bolt is a 10mm head 6x1. There is no way to fit a socket between the plastic of the guide to get the 10mm hex head in straight. I was even trying with a thin walled 1/4" drive socket. I would have had to grind away some of the plastic to fit a socket in there. 8mm heads would have been OK. Allen is even easier.

 

I used the original bolts when I replaced the guide on my machine, It could be that your guide was made near the end of the lifespan of the moulds and you're running into a tolerance issue because of that.

 

Seems odd you can’t get the bolt in, can’t say I had any issue with the original 10mm hex head….something doesn’t sound right with your guide, got a pic?

 

Yup. Stupid mistake. For some reason I was convinced that the "teeth" of the chain guide faced the chain. If you install the guide upside down, it is pretty difficult to fit a hex head bolt into the rear tab. However, it is more difficult (basically impossible) to install the starter clutch when the chain guide is upside down.

 

If it’s any consolation, I’m clearing out my classroom for the summer and just sliced my forehead open while picking a pencil up off of the floor. The aluminum shelf under the whiteboard is sharp.

 

Yikes! I guess you win today, @k-moe !!

 

No consolation at all. I'd much rather that nobody injures themselves to try to make me feel better. Hope it's not too bad of a cut. Happy Summer!

What is a bit of consolation is that this forced me to buy some tap sockets which I've needed for a while anyway.

Mezzmo's video is extremely helpful. I'll be consulting it a number of times more as I finish putting the engine back together.

 

OK. This seems weird. At 6:21 in the video, he's installing the middle gear, and there's a half-ring and a seal that fit into slots at the output shaft end of it. I don't have that seal. And I'm pretty sure I didn't just misplace it. The crankcase has a slot for it, though. What would be the effect of missing that seal? My bike has 14K miles when I got it, and it was about 15 years old at that point. Any chance someone else has been in the engine before and didn't reinstall that seal?

 

For some odd reason.....which I don't fully understand......only the 1980-81 XJ650 Maxim, 1982 XJ650RJ Seca, XJ650 Euro 4K0 models, and 1981-82 XJ750 Seca engines use that seal. All other engines do not use it. And just looking at the parts diagrams, I can't see where any changes in the engine cases that would obviate the need for the seal. If anyone has any further insight, please spew......

 

Although, looking at the Mezzmo video at about 7:20 - 7:35, I note that there are 2 different bearings specified in the position:

a) a B6304 bearing, specified for use on all XJ650 models (except Turbo) as well as all XJ750 air-cooled engines except 1982 XJ750 Seca engines. Also, it is a 57mm OD bearing (even though, according to ABEC specs, a B6304 bearing should be only 52mm OD........)

b) a B6204 bearing (47mm OD) in the same position, used on XJ650 Turbo, XJ700 all, XJ750-X, all XJ900 engines, and the 1982 XJ750 Seca engine.

The width of both of these bearings are the same (20mm) and both have the plastic shield on one (the outer-facing) side.

Although it's understandable why a change in bearing sizes may have been initiated by Yamaha for one reason or another, it's odd that the 1983 XJ750 Seca engines were "passed over" in the change, as I would suspect that the B6204 bearing is an "upgrade" in some way/shape/form, or otherwise it would not have been changed. The B6204 bearing is used in all of the "heavier duty" engines, i.e. 650 Turbo, 700's, and 900's.

And it took some significant changes in machining of the cases to accomplish this bearing size change.....

AND....it almost (but not exactly) lines up in applications with the change in the "oil seal or not" applications.....hmmmm.

I would also note that sometimes parts books are incorrect in applications, especially after a part goes thru a couple of supersedes.

Again, if anyone has some insight into this, would really like to hear about it.


Paul.....what size (OD) is your bearing?

 

I have not removed the cover over that bearing, so I can't easily tell. That's one at the end of the 5th gear, right?

 

Correct.

 

WAG Yamaha engineers were toying around with the oil level in the beveled gear cavity - perhaps because they knew no one pulls the middle gear drain screw as it required exhaust removal

 

That is a very interesting idea.......

 

I think I'm going to reassemble without it. I doubt that seal (or lack of it) is why my starter clutch bolts backed out.

 

I believe that is correct unless you have the cutouts for the lip of the seal. You can see cutout very clearly in the Mezzmo video and in this Ebay ad

https://www.ebay.com/itm/232869531514?hash=item36381b0f7a:g:WQkAAOSwq4VbUN-y



And this one labeled Maxim on Ebay with no cutout for the lip seal

https://www.ebay.com/itm/124492774827?epid=1123584140&hash=item1cfc58fdab:g:CKoAAOSwFzZf3S-S&amdata=enc:AQAHAAAA8JGn8b2yg0bfMkTF7IYPKD7IxD8rCMMRw23Au3jNko+o2Si1gAbazqE9Lm311X+oPzlfj2jTl1Gmfb/YvfyzRrssWdvRjXnikxqCui4spun5mgb3Ov6PHIJrdfHvmeKrrn7hqv2vJF2pt1tyf6WLzRleqHYHwaxqWAPqE/nPtu0K/0UhItEB+Up1jnLStXeABW7dphej+ccASSbMIzI0JXPUFNKDQwAaDFHzVWZkIMotVU3L7O27NJlJEssh1xM/MMgUIqquTcgxZcl9D7NQibUQk65ZLoy+yHoiQ3jxgqktkJZUbixXaga9guxWw7zC2g==|tkp:BFBMxp6tuaZg



cds1984 did not have the seal in his pics but also doesn't have the cutout for the seal lip

https://www.xjbikes.com/forums/threads/xj750-engine-removal-and-split-pictures.38545/

 

Good research Rooster!

 

My crankcase does have the second slot for the seal.

 

Here's what mine looks like. There is maybe a bit of gap for the seal? Also, mine has two half rings for the upper transmission shaft, where all the other slots use one half ring. Is that expected?

 

Not sure what you mean by "half rings for the upper transmission shaft, " are you referring to the circlips that are shaped as half rings?

Item 29 and 31 in left view item 10 in right view - each callout for just one at those locations



Note also the bearing in your picture is installed backwards as the groove should be away from the middle gear so that indicates the bearing was removed at some point and perhaps the seal with it. Did you see any witness marks that perhaps the cases had been split before, like maybe where the screws were staked for the middle gear Torx screws

 

I'm talking about item 11 on the left. I have two of those.

I don't understand what you're saying about a bearing being backwards. The middle gear goes to the right in my picture. The bearing number 30 is with its slot away from the middle gear.

 

OK on item 11, but it looks like just one called out. I seem to remember someone else brought that issue up lately but I don't remember the specifics

 

So back to item 11 I did find another thread where the consensus seemed to be two circlips. The parts diagram only shows one, but the part quantity is listed as two so yes there should be two there
@chacal - do you even carry that middle gear seal, it is listed as unavailable with Yamaha

 

Yes we do, and Paul has already ordered one:

HCP20944 Aftermarket middle driven sleeve gear output shaft OIL SEAL, fits onto the output shaft where it exits the crankcase housing behind the bearing plate “half-moon” retainers. For all 1980-81 XJ650 Maxim and Midnight Maxim engines, 1982 XJ650RJ Seca, XJ650 Euro 4K0 models, and 1981-82 XJ750 Seca engines.

 

OK. I see what you're saying. Thanks.

 

Got the parts yesterday. The seal is installed and fits, but definitely adds some drag. I expect that's normal. Getting ready to put the two halve of the crankcase back together.

 

Some good progress today. The engine is back in the frame. Still need to bolt it in place, and put the clutch back together, but getting there.

 

What do you folks think? Are these factory marks, or something added during a rebuild or salvage?

 

Factory.

 

Here's one more

 

Where is that 2nd scrawling located?

 

I'll have to double check later. I think they're both on the back edge of the engine near the right rear corner.

 

It's at the rear edge of the engine next to the clutch cover. One on top half and the other on the bottom half of the crankcase.

 

There factory marks to show bearing and spacer sizing for crank and drive gear. Pretty sure it’s explained in the manual.