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Carb issues

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M0WBY:
Hi

Took the head off tonight. Bit disappointing really I was hoping for something that I could blame the issue with cyl 4 on but I did not. I did notice I was not the first person to go in there. It had the o ring on the left side replaced. It was a bit of a cheap skate job as everything has sillycunt sealer as they obviously used the old gaskets and wanted to make sure they sealed! Which they did not as it happens.

The bores seem to be in good order you can still see the machining marks from when they were bored out or maybe it has had the bores honed. The head gasket was fine. Nothing to report. From visual inspection the valves seemed to be seating. There was no scoring of the bores by the piston rings that I could see.

Early days yet. I may get the head pressure tested. Seeing as I am in there I may get the valve seals replaced. Unless they find something i will leave the valves alone. Or possibly get the seats re-cut and new valves and seals if there is any question regarding them!

Next will be pulling the barrels off and seeing what shape the piston rings are in.

Ho hum...

Cheers

John

M0WBY:
Hi

Going to remove the barrels when I get a minute will have a look. I hope this is my issue. A new set of rings are in order I reckon! I have removed pistons on cars before but never on a mutliple cylinder bike. With a car you do one at a time. This will be a challenge to get all four in! I could do with some tips on getting the barrels back on.

Also on cars (well you can sometimes get away with it if there was no overheating and the head is flat) you have to have the head skimmed. I am assuming it is the same on a motorcycle?

Where is best to get the rings from? My local engineering shop or order them from David Silver?

Cheers

John

Bitsa (Ralph Wright - RIP):
Mowby.
In all my experience I have always decoked valves and ground them in and new guide seals whether they need it or not. I have never had to replace the guides or skim the head perhaps I was lucky .As for the cylinders remove one ring place in bore and measure the gap.If out of speck new rings and I would only use Honda are in order providing the right speck is attained otherwise its a re bore.Again never had to have that done yet.In my mechanic days loads but that was on the small Honda's where the Muppet's never kept the oil changed.For putting the cylinders back on it is not too hard as the bores are tapered I ususally start with the middle 2 sliding them in until you can only just see the piston pin slowly turn crank(the cylinder will move) as the outside 2 come up to meet cylinder guide them in .I use my finger nails or a small driver to push the rings in.If new rings are fine I do usually slightly hone the cylinders enough just to remove the smooth surface gives the rings something to bed into.Also I always test the valves after grinding by filling up intake side with petrol if they are not sealed right you will see it weep through.Make sure you are in a ventilated area and no flames around you when doing this as you probably all ready know.Wish you luck
Cheers
Bitsa

Bryanj:
You will probably find that rings are only available from Honda as the 650 was not that popular, definately while the head is off change the stem seals and maybe lap the valves

M0WBY:
Right guys,

The 650 not very popular? You are not kidding if they all needed a rebuild after 26K miles! Crap is all I can say! Unless somebody changed the Speedometer at some stage!

All the rings were complete. I have measured the rings and what I found was a revelation. I thought cyl 4 would be the worst but apparently not! The HBOL says Nominal ring gap for top and middle 0.10-0.30mm Oil control 0.30-0.90mm

Wear limit top and second 0.7mm Oil control 1.1.

My measurements were

Cyl 1 T & M 0.33mm Oc 0.95mm
Cyl 2 T & M 0.35mm Oc 0.75mm
Cyl 3 T & M 0.85mm Oc 0.94mm
Cyl 4 T & M 0.38mm Oc 0.94mm

Cyl 3 may needs a rebore.

The piston ring grooves were fine.

Cyl 1 minimal carbon in the grooves
Cyl 2 clean as a vicars underwear
Cyl 3 Ye gods!!! More carbon than you can throw a stick at!
Cyl 4 A bit of carbon

So in concluesion it is cyl 3 that is shagged so I am no better off knowing why it was not firing on cyl 4!

David Silver has original Honda rings in Std size. He only has 2 sets of 0.25 over size and none 0.50 over size!

So if I end up getting it rebored I am guessing the engineering shop will tell me which size pistons and rings I will need and I hope they are not 0.50 over!

As soon as this thing is rebuilt I will run it in and then get shot of it before it needs reboring again!

Nah only joking this thing is with me for the longhaul! Grr even if it does need rebuilding every 3 years! ROFL

Poor old girl http://www.flickr.com/photos/discoclover/8105888596/in/photostream http://www.flickr.com/photos/discoclover/8105869705/in/photostream

Got a beer to drown my sorrows feeling it is not the only one I will be having tonight!

Cheers

John

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