Diagnostics - Inlet Rubbers and O-Rings.

Saving the diagnostic heartache.
If you had to name a fault on an engine that causes no end of diag. grief, it's an inlet air leak. From a worn carburettor to a knackered O-ring, any extra air sucked in with your [perfectly] metered fuel will have you chasing round the bike looking for obvious problems. Not always easy.
So, if you're trying to put together an old bike, be sure to change the O-rings on the inlet rubbers while you're at it. Why? Take a look at the picture below. This is the combined result of thirty years of engine heat cycles, and intense Australian sun. The O-ring on the left has turned into a flattened, plastic ring - no longer supple, and no longer sealing. When compared with the new O-ring on the right, it's easy to see why it won't work.

But before changing them, check the manifolds themselves. Although the rubber tubes on my GSX have hardened, I can't find any splits and a quick clean up should have them ready for use. The next step was to run a blade around the inside of the inlet tube where it meets the cylinder head. There was a rough, raised edge on each of them (either rubber or carbon) so I cut it away and smoothed it with 180 wet & dry. 

Next was to make sure the surface was flat. Anyone brought up on Brit bikes with Amal Monobloc's or Concentric's will know this scenario all too well. Previous gorillas (ok, owners) tightening up a two-bolt flange like this tend to warp them, allowing a nice supply of unmetered air into the engine. Luckily, these particular inlets are held by Phillips screws, which generally prevents over tightening, but I still clean them up on a flat plate with a sheet of 180 emery cloth. Why take chances?

See how the new O-ring sits proud of the groove, ready to seal both surfaces together.

Perfect!

Make sure the mating surfaces are clean and shiny. Any dirt left here will cause you grief. 

 

Sorted! I've even made sure the "lefts" are fitted to the left, and vice versa. Is there any stopping me?

And moving on... 
With old gasket eventually scraped off, I thought I'd slap the clutch cover back on. It's far easier to clean gaskets off with dowels removed. Again, you need every bit of the old gasket off. Don't expect a new gasket to seal around tiny lumps of old gasket. Spend the time to get it right. A clean surface with a new gasket shouldn't need any additional sealant. 
While you're in there, clean any crud out of the threaded holes with a tap or thread chaser. Even run a larger drill around each hole (by hand) to remove any raised/stretched metal from over tightening. Easier to sort out this stuff now.
With dowels back in place, the gasket has something to locate on.
If you don't have the correct tap or thread chaser, make your own using a bolt of the correct thread - see this post.

Personal preference is a light smear of grease on the dowels to prevent corrosion in the alloy cases. Then offer up the cover and push it on squarely, before tightening the bolts in an even sequence. 

Great! Hopefully oil tight too.

Repairing Threads (On The Cheap)

Getting you out of a hole.
At some point of working with bikes or cars, you'll be faced with a thread that's been damaged through over tightening, cross-threading, or simply full of corrosion/paint. A good set of taps and dies, or a thread chaser set, is invaluable for these times, but here's a neat trick that can get you out of that hole when you have neither.

But first, here's a few of the sets I use regularly. Well worth the investment, even it only saves you once.

Snap On Thread Chaser Set

M10x1.25 Chaser, Nut andTap

Beta Tap Set

Now the cheap method.
1) Take a bolt of the correct thread. 
In this case an M8x1.25 - this refers to the diameter of the bolt, not the size of the head (M8 = 8mm), and the pitch (distance between each raised point in millimetres).

 

2) Cover the thread in rag, and place the bolt in the vice. 

3) Take a square, triangular or flat file and start to cut a slot into the end of the bolt.

4) Once it starts to look like this, turn it 120º and cut another slot. 

5) Repeat one last time so you have three slots around the bolt. These are going to carry the swarf away from the problem thread, and prevent further damage. 

I use plenty of WD40 when clearing threads in aluminium, and take my time. If it tightens up, work it back and fore, and spray with lube until it frees. 

If you can't work out the correct angle the bolt should be screwed in (due to cross-threading damage), see if you can screw some other bolts in surrounding holes. This will give you a guide to follow when you're trying to get it back on track. Similarly, a spark plug will normally follow the same angle as the others in a multi-cylinder engine. 

Take your time to work out angles before screwing the chaser, or tap, into the hole or you'll cut a good thread at a crap angle!

The budget thread chaser. 
This can also be put to good use with old spark plugs if somebody's managed to cross-thread them or the holes are full of old carbon etc. Just slot an old plug in the same way. One thing to remember, your budget chaser isn't as hard as the correct tool, so don't expect it to keep clearing in the same way. This is more about getting you out of a jam on a Saturday afternoon when those vital stores have closed.

  

Suzuki GSX750ES — Painting the Engine.

Yeah, so it's been quiet lately.
A twist of fortune gave way to some time in the garage, which meant a little more got done to the GSX. I'm currently zipping between little tasks on the bike  and not getting anything finished. And one job I did want to get out of the way was a splash of paint on the engine. 
I initially thought I'd go for bare alloy, except for barrels and head, but thirty years of corrosion was proving hard to remove. It would have been ok with constant polishing, but I relented and chose to paint it instead. 

It took a lot of cleaning from this: