Topic: 1972 CB500 - Rebuild Project

[Puffin]

Couple more pics of the increased tolerance...

[Puffin]

Engine is sittingl in the frame and buttoned back up.  Went in like a dream with two people.  I took off the sump pan and the breather cover and it slotted straight in.

Whilst I was there I ground off some of the powdercoating from the mounting brackets to ensure I had a good earth from engine to frame.

[Puffin]

The front end was only mocked up so I finished the final install now that the bike was carrying the weight of the engine. 

When it was all tightened up I had a problem with the caliper arm sitting and rubbing on the brake disk.  The caliper arm had some vertical movement so I took it back off the bike and dissembled the 'pin' that holds the caliper arm to the fork.  Once disassembled the pin looked ok but the o-rings had disintegrated and I noticed that the arm itself had worn slightly at the top and bottom where it sits on the 'pin' which was causing the slack. 

I found a thin washer and used it as a shim between the pin and the arm which seems to have solved the problem. 

Luckily the o-rings for the caliper arm are also the same size as the O-rings used for the engine valve guides so I had several new o-rings sitting in my Vesrah Gasket Set.

The arm is still quite close to the disk but even with the weight of the caliper it's not touching so I guess that's good enough...

[Puffin]

Mocked up the new headlight bucket and brackets and popped the tank on.  It actually looks like a bike again which makes me feel like I'm almost there... 

Headlamp is just a plain matt-black Emgo job... really simple but I like it. 

I wasn't too sure about the headlight brackets when I got them, they were a bit shiny.  Now they are on the bike though I like them.

Can't quite work out if I have them upside down though?

[Puffin]

Haven't bought anything for a while so I made up for it by ordering a new Dynatek Electronic ignition.  My old points were bent and looked pretty knackered so given that I had already got new Dyna Coils I thought I'd splash out a bit more and get the full system.

Also made a bit of a impulse buy and ordered a set of super wide, old school, black, dirt bike bars with the cross-brace.  Not sure if they are going to work on this bike but and I figured I can always use them on something else or sell them.  The existing bars have been cut and are too narrow for my liking....  If my new dirt bike bars look daft I think i'll go for a set or Superbike or Tracker bars... something wide with not too much rise or pull-back.

[Puffin]

My brother living  on the other side of the world messaged me the other day wanting to know when my next update was coming... apparently the anticipation is like waiting for the next series of Game of Thrones!

That made me laugh so just for you BombHead....

[Puffin]

I have been busy on the bike working on the carb re-build. I basically stripped the carbs down and gave them a really good clean.  Putting them back together was not too bad... once you figure out the first one the other three fall into place.  My advice is to take lot's of photos as you go as there are a lot of little parts in each carb and the Parts Manuals don't show a breakdown of all of the components.

I have spent quite a lot of time on the forum getting advice and reading through other build threads which also helped a lot.

My carbs were in pretty good nick and really didn't need much work apart from new rubber and a good clean.  I did get a rebuild kit but ended up also getting better quality o-rings and making sure I re-used the original Keihin brass jets where possible. 

I did a bit of a review of the re-build kit I ordered and posted it on the forum if anybody is interested.

http://forums.sohc4.net/index.php/topic,149097.msg1700597.html#msg1700597

[Puffin]

My old float needles were sticking in their seats and not releasing even after a cleaning so I swapped them out for new ones.  The new needles sat slightly higher (0.3mm) than the old ones so all my float heights were slightly too high.

I fashioned a high tech float height gauge out of an old loyalty card and set the float heights back to the factory 22mm. 

Later I'll run some clear tube out of the float bowl drain plug once the carbs are back on the bike and double check the actual fuel level just to make sure everything is correct.

[Puffin]

For no other reason than self-indulgence I treated the carbs to some sexy new Stainless Steel screws and sourced some cool cloth covered fuel line.

The original fuel line was 5.5mm, which is actually tricky to find in the usual auto-parts stores, but I discovered that this is the same size that VW used on their Beetles, Carman Ghias and Camper Vans etc. 

The aftermarket supply for these vehicles is massive so once you are armed with this knowledge finding new line is easy.

[Puffin]

Installed some nice new soft Carb Boots also went on ready for the carbs.

I'm going to run the bowls and the top caps over the polishing wheel and then I guess that's another job done..

One question somebody may be able to help with is where to set the throttle slide height after a re-build?  I've basically just screwed the adjustment screws to the point where the throttle slide just barely touches the base of the carb.

Should I add another couple of turns?

[Puffin]

Happiness is....  a bank of fully restored, cleaned, polished and Sync'd Keihin 627b's.

[Puffin]

The bike had no mufflers when I got it and so I ordered a pair of Emgo 17.5inch Reverse Cones.  I like the balanced look of a 2-into-1 set up and I would be able to make this work with only minor modifications to the existing headers which had been cut and welded (badly) already.  I had read they were pretty loud though and I need to get the bike through a compliance test in order to get it back on the road.

When I took the baffle out the packing was pretty awful... just a tiny amount of what looks like roof insulation.

For $20 I got some proper muffler packing delivered... although I now have enough to pack about 100 mufflers.  The new packing is much thicker and much better quality. 

The reason for the odd shape I cut is that the mufflers are cone shaped therefore can take more packing as the muffler gets wider.  Not sure how much this is going to help yet but I figured it can only help.  Process took about 10 minutes.

[Puffin]

Now that the carbs were on the bike I hooked up an auxiliary fuel line and connected a short length of clear tube to the float bowls using a 5mm 90 degree plastic tube connector. 

I'd read a lot of people drilling out a float bowl screw and threading in a brass extension with which to attach the tube but to be honest that just sounded like too much work... this cost me about $5 all up and took 5 minutes to install.... so long as you screw the connector in slightly it works perfect, no drips.

The idea was to make sure the fuel level in the bowls was high enough and even across all 4 carbs, especially as I replaced the OEM float valves with aftermerket parts so I couldn't guarantee the factory float height was still correct.

Looked pretty good.  All were about 5mm off the bowl to carb gasket level.

I would have liked the fuel to be a couple of mm higher however but I'm going to have to pull the carbs back off (for reasons I'll explain later) so I may adjust the floats slightly later.

[Puffin]

So I've been really struggling with getting the front and rear wheels, and the drive sprockets to all line up together... I must have been at it for a month or so now but I keep finding potential issues and It's getting really frustrating.

It started off when I installed the new chain.  If I line up the back wheel using the marks on the swing-arm the chain 'rattles'and 'pops' on the rear sprocket.  I tried various methods and checks in case the marks are not accurate but no matter what I do I can't get it to sit evenly on the sprocket. 

I can see clearly the sprocket is being forced off to one side under the tension of the chain even when the chain is quite slack.  This implies to me that the front and rear sprockets are not aligned.

My initial thought was that the rear sprocket is more likely to be the culprit so I disassembled the rear wheel hub in case I had installed a spacer wrong or had the new bearings not seating right.  Everything looks good however and I double checked the order of the spacers against the parts fiche...

At one point I had some concerns about the bearing retainer which clamps onto the wheel bearing but has a gap that allows the sprocket holder to 'float'in the hub.  The advice I got in the forum however was that this is correct.

[Puffin]

My next step was to make sure the rear wheel was properly aligned so I used the string method to align the rear wheel with the front wheel. 

You can see that my problem now is that the front wheel does not seem to be in the same plane as the rear wheel?  I would expect the front wheel to sit evenly between the strings but you can see the gap on the drivers left is significantly greater than on the right...

Reasons for this would either be that this is normal or I have a bent frame or bent forks or I've assemble the front end wrong somehow....

Whilst lining everything up I also noticed that with the front wheel straight the handlebars are not level.... You can't see the bubble in the picture but it is way off to the left. 

[Puffin]

Cal you are correct... I am getting befuddled by piling up the issues and looking for an overall solution.

I was going to post a few more comments and photos after my last post but I got distracted by going to the pub.. I tend to find this happens a lot?

I can address a few of your questions quite quickly...

"It's hard to see from the pictures, but is the rear wheel assembled with the correct spacers? Does the rear wheel (rim) spin freely and without obstruction on the axle?"

This was my first assumption and I have checked and checked again and I can only conclude that everything along the rear axle is correct.. I will post some pics as a fresh set of eyes may pick up something I have missed.  The rear wheel spins beautifully on the rear axle and there is no obstruction.

"For the front end, first thing I'd do is to release the tension on the triple trees and allow the forks to be adjusted. But, is the steering stem bent is my concern? This would show by rotating lock-to-lock and feeling for rough spots in the steering bearings, and leveling the underside of the lower and comparing it to the upper clamp."

I did release the tension in the front forks and this led to my next discovery... bent front fork tubes. (see Pictures below).  No idea how i missed this?  It's subtle... but they are bent without a doubt.  Hopefully I can get these straightened?  A bent steering stem or frame is still a real worry though..  particularly if I know I have bent forks, misaligned sprockets and a ding in the alternator engine case.

There is definitely no rough spots on the steering head bearings.  I replaced the bearings with new All-Balls tapered bearings and they run real smooth.  I double checked them and they are installed ok. 

When I installed the tyres I tested the wheels for 'trueness' on a jig and I was happy at the time that they were good.  I will double check again.

As suggested I will go back and check the sprocket alignments with the straight edge and follow your 3 steps below..

Your suggestion of setting up the string box is interesting and a method I've not heard of before... I'll give it a go.

[Bootsey]

That's a shame about the forks, but hopefully some new tubes will get everything back on the straight and narrow.

[Puffin]

So I have sent the feelers out to see if I can find some new, or decent second hand, fork tubes and I've also found a couple of places that advertise that they can do fork straightening.  I need to give them a call this week.

Given that I can't really take any decent measurements around aligning the front and rear wheels till I get straight forks I'm a little stuck for now....  I may take the bike down to the frame shop and they will run a full alignment test using some fancy computer and a load of probes.  This is about $250 for the test ($175 USD or 100 Quid UK) but to be honest it may be worth doing just for the piece of mind.

Couple of other things I have found that also point to frame issues are an uneven gap where the upper-front engine brackets sit ... see pictures below

[Puffin]

I took the front sprocket back off and noticed that the back side had been wearing much more than the front side which indicates my current problems were obviously in place before I took everything apart.

The front sprocket also had '17' and '750' stamped on it...

I know 17 teeth is correct for a CB500 front.  But would a 17t CB750 sprocket and a 17t CB500 sprocket be interchangeable?

There was also quite a lot of play on the front sprocket... is that normal?

 

[Puffin]

Some pictures of my rear wheel and axle set up...

You can also see how that with the chain on, the sprocket retainer is being forced inwards towards the front of the bike and being forced outwards at the rear.  With the chain off everything sits nice and straight. 

[Puffin]

Thanks for all the advice Cal,

Good news is that I managed to track down some new-old-stock fork tubes locally and they arrived this morning.  I didn't realise before how much the bent tubes were affecting the performance of the front shocks... with the new tubes in the whole front end is so much smoother and it's made a massive difference. 

They look so much better as well... no more dull and pitted chrome for me....

[Puffin]

This weekend I am going to set up all the string lines as per Cal's suggestions and test the frame.  Now I know the front forks are straight i've taken a variable out the equation which is a step in the right direction

For now I've un-buttened all the engine bolts and I can already see that the frame-engine spacings in various locations has changed so something is definately wrong.  I'll tighten them up in the order Cal suggested and see if this makes a difference.

In the meantime I did a quick test using a level

1)  Level at rear of frame - Dead level
2)  Level in middle of frame - Dead level
3)  Level at top of triple clamp - Dead level
4)  Level at base of triple clamp - Dead level

Result = Font wheel is pointing right

If I turn the wheel so that it is pointed dead ahead (visually) then the level at the triple clamps goes off level.  The middle and rear of the bike frame remains dead level.

To me this simple test confirms that the frame is slightly twisted... this would account for the front end angle being off vertical and could also account for the sprocket misalignment if the engine is not sitting in a straight frame.

[Puffin]

So haven't posted for a while and progress has been a bit slow but I'm hoping to speed things up again now I have had my frame sorted.  I'm supposed to be riding this bike round New Zealand in February and there is still a load of work to do before she is ready for such a trip.

Good news is that I found a guy a couple of hours away who straightens frames so I bunked off work for a day, popped the bike in my van and drove down to his workshop so he could take a look.  He did a few tests and turned out the front end was twisted.  $250 and half a day later he had it all straightened out and lined up again.  He also straightened out my front wheel that had a bit of a bulge in the rim.

Happy that is sorted

[Puffin]

I also found out what is causing the issue with my rear sprocket...!

Here is my problem.... excessive play on the final drive flange...

[Puffin]

You can see from the pictures below that the internal 'bush' inside the drive flange is really badly worn.  The grease grooves have almost completely worn away and you can see a lip that indicates how thick this bush used to be...

I have attached a picture of a new drive flange for comparison