Topic: Strange smell to exhaust and low compression. HELP?

[Kingscorpion]

Hello all - SOHC 4 Newbie here.
I am overhauling a 1971 500/4 K0 in the UK. Its a USA import. Low miles <2000 but has been standing inside for years.
I am baffled by some issues with this bike as follows and wonder if anyone here can make sense of this:
1. Starts absolutely first dab of the starter or even by HAND on the kickstarter!!
2. Makes irrritating amount of whitey/grey smoke most of the time.
3. Compression tester shows less than 50psi on all 4 cylinders.
4. Exhaust smells kind of sulphurous/ steamy and continues to smoke a little after engine stopped. Noticed water dripping from exhaust drain hole.

The engine has just had new standard rings fitted!!! There was no damage or signs of wear to the bores.

Am I right in thinking valves issue here? Although I saw no problem when the head was off and all is working smooth and quiet. (Only thing I did find was a thick and hard to scrape off tan  coloured residue on the valve heads).

Any ideas what is causing the smoke?? Is this a common issue? The exhaust smell is just not right.
 

[Hush]

The low compression I would suspect was valves not sealing correctly as you suggested since you have just done new rings, I'm no expert on valves but some on here are wizards...wait for a wizard.
Any bike that sits for any length of time will build up condensation, this comes from oil/gas as they are essentially partly water.
I have struck this on many bikes that I have ressurected even the modern ones, if it runs OK I'd let it heat up a bit to let that condensation become steam then it can escape via the exhaust pipe, some water will drip from the exhaust pipe as it warms up, that is all normal and it will be brown like tea without milk.
If that smell does not go away it "could" be petrol in the oil, once carbs overflow they can dump straight into the sump, it is quite hard to tell if the oil is contaminated by gas, if you suspect this I would throw the old oil away and a new oil filter.
Hey this may be helpful, maybe not but it's what I would do and have had to do in the past.
Have fun..

[dave500]

take it for a good clean out fang!dont baby those new rings you wont hurt them,you sure your gauge is right?50 psi sounds low i fart harder than that,did you have the engine hot and the throttles held wide open when it was done?
also was the battery fully charged to spin it nice and consistant?

[phil71]

Your compression tester must be naff. No engine with those numbers would light off so easily. As for the smoke, you can't really make any determination there till its run for a bit. New rings ought to mean assembly lube, and that will take time to burn off, not to mention deposits that have surely built up in the "elbows" of the pipes.  If all else seems okay, run it more.

[Kingscorpion]

Thanks for the suggestion - Even after a good run its still making the same kind of steamy smoke. It just looks/smells as if something is wrong. I thought rings so stripped it down and put in new R marked rings. (One middle ring on no2 cylinder was broken I discovered) but this has made absolutely no difference to the smoke!
The valves/rocker gear all seem to be perfect, new base+head gaskets fitted and all O rings renewed.
Running 10/40w semi synth oil and regular unleaded fuel.

Still I get this weird smelling exhaust smoke - kind of like the smell from a coke fired boiler or a steam engine. Could it be the valves are not opening correctly and allowing some kind of  mixed up compression cycle?
This is really frustrating. Am I wrong to expect a clear/ crisp exhaust emission from a 40 yr old engine?

[dave500]

if you had the valve settings wrong it would run like #$%*,not smell like it,is it just external grime burning off?you are revving this thing over 5-6 grand off course?lots of city traffic idle slow driving might cause a build up of sorts and not ideal for bedding in new rings.

[dave500]

umm?you honed the bores before the rings were installed?

[Kingscorpion]

Hey  -good point maybe I am being too gentle with the revs. I was just letting it idle and keeping cool with the breeze outside (temp here about 15 degrees C this week!)
There is definately much more compression I can feel on the kick starter and when I turn the crankshaft nut with a spanner than before.  So yeah maybe a duff tester.
Can I confess at this stage that I did run the engine a short time without the mufflers attached and noticed intermittent blue flame ejecting through the exhaust ports. Could it be somekind of afterburn in the mufflers creating this smoke?? By the way they are brand new mufflers.
Its just like there is something in the burn or oil in there somewhere but the smoke is white/grey not blue/white.
It kind of hangs around in my garage but is not clouds more like a mist.
When I switch off the engine wisps of it continue to emit from the pipes for a good 5-10 seconds.
Its difficult as I have no reference point of a 100% healthy SOHC 4 to compare - only a 2002 Bonneville which emits nothing.

[Kingscorpion]

Dave  - no I judged the bores were ok and went on advice that honing is not really necessary with a standard ring change?
Did i do wrong??

[dave500]

yeah,you should hone the bore to break the glaze or mirror looking old surface,do you feel like opening it up again to do it?i would,you will be able to reuse the head gasket again its still that new and not baked on,the base gasket aswell if it comes away clean.were the valves removed from the head and lapped and new stem seals used aswell?if not nows a chance to have a good second go at it,a good experience at doing it again,,nothing wrong with that its a learning curve,dont forget even the best race teams will re build engines over and again in one day!

[Kingscorpion]

HA looks like I am gonna be tearing it down again! I thought wrongly I guess that the smooth walls of the cylinders were a sign of good condition! As the miles are so low on this bike seemed like I'd get a better seal with the new rings and this smooth surface?

Valves etc seem to be in fine condition but I guess I will have to go back in there and check (after all I did get new seals in the gasket set)

But  -I did notice that i got a better compression reading with a squirt of oil AFTER the new rings were fitted could this still be due to the lack of honing?

There was no noticeable step or ridge at the top of the bores just a thin ring of carbon crust. No scoring or wear visible - cylinders just had that grey /green /goldish colour to em. All rings were spaced correctly and clearance etc was bang on.

Would the new rings eventually seat after time even with no honing?
By the way its a below CB500e 1006000 engine number.

[trueblue]

+1 hone those cylinders.  The rings will never give a good seal if the cylinders aren't honed.  There are a couple of bush mechanic/rough c^#& methods to bed the rings into a bore that wasn't honed but I do not recommend these in any engine you want to keep for any length of time.  Also replace those stem seals, after 40 years they'll be as hard as a rock. It also wouldn't hurt to check your valves for sealing while your at it.

[DJ_AX]

Brand new mufflers? Could it be paint or sealer on the inside cooking?

And I've never thought of doing a compression test in my butt! 

[lrutt]

yup, got to break the glaze on those cylinders for sure. while in there, do the acetone test on your valves to check for seating, as in poor acetone or gas or some such solvent in the ports and see if it seeps out around the valve head. If so, lap them in.

Do not run an engine with no head pipes on if that is what you did. You can warp a valve supposedly. No muffler is kind of ok but will run like crap due to carburation being messed up. No head pipe is a definately no no.

When I did my 650 Triumph, I honed the cylinders for the new rings and got it running and it smoked like crazy. Never ever had that before after doing a top end refresh. So I took it out and thrashed the crap out of it for a few miles and it cleared right up. I killed a lot of mosquitoes though in those few miles. But it's been clean and smoke free every since.

[Kingscorpion]

All I think I may have stumbled over the answer to all this.
When I stripped down the engine originally I found that the chrome compression ring marked R was the middle ring on each piston. So I replaced with the new rings in exactly that order.
Top: the cast iron ring
Middle: the chrome edge ring
and
Bottom: the 3 piece oil control ring.

Now reading other posts it appears that the chrome edge ring should be on the top?

Can any of you experts confirm this?

Could this be causing the trouble I have been having (and still will be till I have stripped this down again!!)

[raymond10078]

See attached - seems to answer your question.

[phil71]

That still won't account for the smell

[lucky]

Your compression tester must be naff. No engine with those numbers would light off so easily. As for the smoke, you can't really make any determination there till its run for a bit. New rings ought to mean assembly lube, and that will take time to burn off, not to mention deposits that have surely built up in the "elbows" of the pipes.  If all else seems okay, run it more.

Maybe he did the compression test with the throttle closed.
Maybe he did the compression test with the spark plug in the other 3 cylinders.
Maybe he performed the test with a low battery.

 

[lucky]

All I think I may have stumbled over the answer to all this.
When I stripped down the engine originally I found that the chrome compression ring marked R was the middle ring on each piston. So I replaced with the new rings in exactly that order.
Top: the cast iron ring
Middle: the chrome edge ring
and
Bottom: the 3 piece oil control ring.

Now reading other posts it appears that the chrome edge ring should be on the top?

Can any of you experts confirm this?

Could this be causing the trouble I have been having (and still will be till I have stripped this down again!!)

The rings usually come in a package and all you have to do is install them in the order they are stacked when you get them.
If you have questions did you call the manufacturer?

If you did not hone the cylinders before putting in the new rings you would have to take it back apart anyway. It would just keep on smoking.

[dave500]

yep chrome is the top ring,the marks on the rings go up,also check the ring gap with the ring about halfway down the bore,position the piston on top of it to square it up.

[Kingscorpion]

Well Folks after a marathon strip down this evening....guess what?
Yep chrome rings fitted in position 2 (one down from the top!)
So looks like a suspect to me.
Gonna hone the bore tomorrow and replace the valve seals.

Weird thing was I started her up before the strip just to convince myself that it had to be done and got a strong kindof cordite smell rising up from around the exhaust ports (pipes and mufflers connected and tight but not torqued down.
Strange.

I will report back with developments on this puzzle IDC.

[Hush]

Wonder what the smell is?

[trueblue]

Really old or really crappy fuel can cause a sulphur smell, I've seen/smelt it a couple of times.

[Kingscorpion]

This really is strange  - I just hope rebuild no2 will sort the issues!

Just ordered a flex hone kit! Got the rings back on the right order (but was surprised to see the first signs of wear on the rings?? Some of the black colour of the cast iron rings has worn off and they have only been in the engine 48 hrs!
I just mic'd the bores again and with a vernier caliper I am getting readings of 55.78 - 55.92 on all 4 bores. So I judge that as very little wear?

Incidentally while stripping down I checked compression again with the rockers off. (ie all valves closed) still got very low readings around 40psi so suspecting my tester is off. Put my thumb over the plug hole and cranked the starter. Very little puff but masses of suction nearly pulled my thumb into the chamber!!
This all seems to indicate that getting the rings in the Wrong order might be significant! Could be preventing compression but allowing suction..
At this stage I suspect its all caused by a film of oil getting up the bores into the combustion chamber and then continuing to burn in the exhaust outlet (this would explain the blue flame I saw and also the cordite/carbon smell around the outlet). Guessing I have a good enough compression to ignite the  fuel/air/oil mix but it burns just that bit longer than the ignition stroke. 
There was a fair bit of oil/ carbon around the exhaust outlet from the head but the valves look ok and no sign of oil around them.

So I suspect the rings may have been changed at some point over the last 40 years and someone got them in the wrong order!
I then replicated their mistake!

Unless the unthinkable......... a mistake on the original Honda production line??? It is a very low serial number...

Beginning to think I need to invent internet "smell - o - vision" to really sort out this problem.

[ChuckG750f1]

And I've never thought of doing a compression test in my butt! 

We need to ask Dave who sells the adapter for this and do they come in SAE and metrics sizes.  They may only be available in Australia.  Also, do you perform the test with your mouth fully open or closed to get the proper reading?