Carb issues

[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

[K2-K6]

It just doesn't look like there is anything there that would stop it running on those cylinders to me, maybe a bit underpowered or some compromise but you'd expect it to be firing at least.

I've seen engines that are far far in excess of this and although a bit ropey they still run and not bad either, think you are really looking at fueling/igniton as the original problem.

Silicon gasket can be the death of these motors as any loose bits can often be bigger than an oil supply route and very often trash the top end of the motor fom oil starvation.

As Bitsa says, the bores have quite a nice taper at the base so feeding the pistons/rings in there is not a bad job, just take it slowly and you'll feel them go in quite easily usually.

[Bryanj]

I would suggest an accurate bore measurement in several places to see if tapered, oval or out of spec and work from there.

Cylinder bore dial gauge is best---I got one but it might be too far to Gloucester!

[M0WBY]

Hi guys,

Thanks for explaining things oddjob... Please excuse the questions just trying to clarify things in my head! I was a little confused by things and over what exactly I was measuring! I had to go back to the  manual and do some revision!  I have to put my hands up and confess that I have not had to look at piston ring gaps and bores in a long time! I was using the rings with the cylinder they came off. I will order a new set and see how they compare. I think it is the rings that are worn on Cyl 3. Probably was due to the carb issues I am guessing. One thing I noticed the online manuals have you measuring the rings at the bottom of the bore as opposed to the top in HBOL. Measuring them at the bottom makes more sense to me. 

I am hoping that I can just get away with a hone of the bores.

It says in the manual that each ring is marked so you can tell which side is up and also that one should be marked with a T to denote top ring. I have looked at mine and none are marked with a T! In fact the only difference is that each ringset have one ring with the marks 'R N' and the other is just marked 'R'. You are meant to be able to tell which is Top and which is second as second ring is tapered but I can't see any difference! They all look the same to me!

I am hoping the new ones will be marked with a T so I can tell the difference!!!

Cheers

John

[M0WBY]

Hi oddjob,

OK so they are different colours when new that helps...

I am confused now about end gaps and worn rings! I understand measuring the three points to see how the bore is worn. But how does one tell you if the rings are worn and need replacing?

With mine it was obvious because with Cyl 3 rings it was really easy to compress and put them in the bores. The others were a lot harder. The other three seemed to have more spring to them. Is this how one tells they are worn? Seems a bit subjective to me... Still if you are in there you must have suspicions and you would be a fool to pull it all part and not change the rings as part of the course!

But if you had all fours sets that were all as bad surely they would all feel the same and unless you compared them against new ones you would never know! Does this make sense?

Cheers

John

[tom400f]

Yes you are making sense.

Without a way to measure the bores independently (micrometer instead of using a new ring) I suppose you cannot tell. However as Oddjob suggests, one new ring set is unlikely to go to waste but while you are waiting you could:

1) choose one bore and measure all ring sets against it (bore is constant) so you get some idea of how the rings compare
2) use the "best" set of rings to measure all your bores (ring set is constant)

Then you have some comparable numbers for both.

[M0WBY]

But measuring different ring sets on the same bore won't make any difference as they will all have the same gap because that is decided by the wear on the bore surely? Or am I being stupid? Do you see why I am struggling to get my head around it?

Otherwise the only test is the spingyness of the ring and whether it stays compressed in the ring groove?

Perhaps I am thinking about it too much!

[tom400f]

Thinking is good. I am only thinking that if a ring itself is worn then it won't be as wide as a new one and its end gap when inserted into a bore will be larger. I would also imagine a narrower ring would be less "springy". (Note I am choosing my words carefully - I'm not talking about the ring clearance in the piston groove - then I would talk about a ring being "thinner" - just saying).

Since ring wear has been cited (if your bike ran lean for any length of time) then its worth measuring, at least comparatively for now across the sets you have. Likewise the bores - if they are all similar then chances are your barrels are good.

When you get a new ring set you will have absolute measurements and you will know whether you need more.

[M0WBY]

that if a ring itself is worn then it won't be as wide as a new one and its end gap when inserted into a bore will be larger

Why? The ring does not wear on the ends surely? Surly how worn the bore is determines the end gap. Larger end gap = more wear on the bore.

It seems the main issue is how willing they are to uncompress in the bore the rings are. This I would guess is determined by the carbon in the ring gap holding the piston ring closed and allowing compressive gasses down the side of the rings?

I am speculating that the hardness of the steel has something to do with this as well because a less springy ring are easier to compress and might allow gasses past?

[tom400f]

that if a ring itself is worn then it won't be as wide as a new one and its end gap when inserted into a bore will be larger

Why? The ring does not wear on the ends surely? Surly how worn the bore is determines the end gap. Larger end gap = more wear on the bore.

No it wears on the edges, gets narrower and has to expand more to reach the bore. (btw I wasn't trying to suggest it gets "shorter")

As Oddjob says, your measurements at the moment will combine ring and bore wear, until you get a new ring set. Hence I was suggesting eliminating one of those and then the other... just to see a bit more how things are.

[Bryanj]

A piston ring wears in two ways:-

(1) They actualy move up and down in the ring groove as the piston changes direction at top and bottom of stoke and strange though it is the steel ring wears more than the alloy piston.

(2) The friction between ring and bore will wear both the bore and the outside of the ring so that the ring has to expand more to touch the bore hence the ring gap gets bigger.

Now in 30+ years(a lot of those in Honda dealers) i have rebored a lot of Hondas but 99.99% of those rebored were dur to siezures not wear! I can only remember a PF 50 years agp that actually had a wear rindge at the top.

What Tom was saying is if you use only one ring on all the bores you are getting atrue indication of bore wear as all the rings will be worn slightly different

Also if you measured all the rings in only one bore yoou would be able to see if one set was a lot more worn than the others