Topic: '72 CB500 Four

[zojirushi]

Hey folks,

This is my first post on SOHC4, but I have been lurking and learning.  I bought this 500 for a fair price with 55K on the clock and a few nice bits like tarozzi rearsets, tommaselli condor clubmans, and dyna electronic ignition.  Here she is as I dragged her home:

So I did what anyone does, I tore her apart:

The exhaust ports in the head look at least this filthy, too:

Anyone know these rear shocks?  I really like them and would like to find out if they're rebuildable?  PO said they might be some period correct Showa's:



That was the end of the first day.  So far so good, no real surprises, no malicious nuts or bolts.

[zojirushi]

Ok, day 2:
Pushed her over on her side and pulled that greasy old motor out.  I had no idea what to expect out of a motor with 55K on the clock.  To be honest, she was feeling pretty lethargic when I got on her.  There was a really loud chain rattle at idle.  Basically, she was a slow box of rocks.  I forgot to mention the sweet UNI pods that had no oil on them and were covered in duct tape for the first half of the filter area. Oh, I did a compression test prior to tearing down.  Here's the numbers:
1 - 142
2 - 132
3 - 135
4 - 140 
Seems good enough for government, but I still want a look inside.
First I opened up the sump. Bummer:

Here's the problem!

Ok, needs a new primary chain.  Not too much of a surprise at 55k.  At least, it didn't go clean through that oil passage.
Open up the heads:

I think she needs a new cam.  A couple of the lobes have this pitting on them.  Another 500 or upgrade to the 650? 
When I pulled the head I found pistons labeled "0.25" Looks like it's been rebored.  Kind of a bummer since I need to split the cases for the primary chain.  Oh well.  I think I am going to have the valves gone over, too.  That's it for today.  Cheers.

[dave500]

gday zojirushi,take a close look at the bottom of the cam chain tensioner,it looks like someone has miscued the well it suppossed to sit in,the drive hub can rub it when this happens,see how sloppy your primary is,it may have been replaced already?its been rebored so the top end has at least been apart,heres a photo of a wrongly installed tensioner.

[spammasher]

Nice project, i hope it all goes well for you. Don.

[weekend_junkie]

Those shocks appear to be 1981-1982 CB900F shocks.  They are very hard to rebuild.

[zojirushi]

gday zojirushi,take a close look at the bottom of the cam chain tensioner,it looks like someone has miscued the well it suppossed to sit in,the drive hub can rub it when this happens,see how sloppy your primary is,it may have been replaced already?its been rebored so the top end has at least been apart,heres a photo of a wrongly installed tensioner.

Good information, Dave.  I haven't messed with the cam chain tensioner, but I know the PO put in a new cam chain.  This is the original primary chain, so I'll be replacing it.  Ordered a new one from David Silver Spares.  Also ordered a new cam chain tensioner blade.  I will have to refer to the service manual to get a better understanding of how it was miscued.  It may be more obvious to me once torn down and in front of me. 

Thanks for the heads up Weekend.  I guess that's just as well.  I think they'll stay on until I get some new funds in the bank, but they are awfully flexy.

Well, off to the store to pick up an angle grinder.  Today I will tear into the frame and possibly forks if given enough time.  Pictures to follow.

Cheers.

[dave500]

once you get it apart youll see how the lower end of the tensioner should go into a little square well,,you shouldnt be able to see the prong like ends of it once its in place,that might have been the rattle you heard as the chain will run slack.