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?

[lrutt]

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.

do you have the throttle cracked wide open when you're doing the compression test? And are you using the e start or kick start. with e start and wide open throttle. unless you have a big time burnt valve you should get more than that.

Did you do the test as I had mentioned above, ie when the head was off, pouring some gas into the ports and checking for leaks around the valve seats???

[lucky]

QUOTE:
"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."

If the rockers are off and all valves are closed how can it get any compression??

The cylinder develops compression by sucking in air for a certain number of degrees of rotation through the intake valve. Then it compresses that air.
If the exhaust valve is closed how can the compressed air escape?

No wonder your finger almost got sucked in!!!

Can you dial 911 with one hand on your cell phone?

I have never found a wedding ring in a sump yet! LOL...lol

[raymond10078]

If you are using a compression tester with a long/large hose - you will get low numbers.

My compression tester - a Craftstman unit - gives good numbers when measuring car engines - where each cylinder is larger than our whole engine.  On some bikes, with the small chamber volumes, the volume of the hose can alter the results substantially.

I've seen this discussed before - possibly on this site.  Someone even went as far to determine the volume of the compression tester hose (in cc), and then calculated the expected result when the compression tester volume is added to the engines compressed chamber volume.

Regardless, on bikes, the best way to get the most accurate numbers is to use those short rubber tipped testers - which I personally do not like nor own . . . .

[Kingscorpion]

Hmm A compression/ tester debate!

With the valves all closed she should create compression and the only conceivable way out for this is through the spark plug hole.
So with my thumb over it should at least blow out a little on the compression stroke right?

Any way I am using a long hose Laser tester with the right adapter so this might explain a little loss of reading. But not that much.

Engine now too stripped to repeat the test so lets hope the rring mix up has fixed it.

Just checked the ring to piston clearance and .005 feeler just slips in on the top ring and is still a tiny tad tight on the second ring so I judge no problem there.

Re checked the bore with the caliper and I am getting 55.78 - 55.85 readings on all 4.
Pistons measuring out at 54.67 - 54.78

Again all the valves look seated and set perfectly. Checked the head for flatness with straight edge and its A OK.

Gonna strip the head tomorrow and replace the seals.

It must be the rings! Maybe this engine was never run in properly its got 1584 miles on the clock and everything seems bang on spec.

Just smokes and smells like most 40 yr olds.

[TwoTired]

True Synthetic oil can make and odd smell when burned.  It could be the base oil itself or the additives blended with it that create the odd smell.

In a truly unfair labeling allowance, some synthetics are simply a step more refined crude oil than actually created molecule by molecule.

Was your synthetic oil PAO?

Compression:
If the valve can't work, air entry (to be compressed) enters the cylinder through the spark plug hole.
If you plug the hole with your finger when the piston is at top of stroke (and no other valve action), your finger becomes the air control valve, and the cylinder can create vacuum only and no pressure.
If you plug the spark plug hole with your finger, and the piston is at bottom of stroke, the pressure will likely will blow your finger away from the hole (releasing air), until the piston reaches top of stroke, whereby it can only create vacuum until your finger is ingested.

Pressure, or vacuum is created by the piston changing the volume that is containing the gas.

The CB550 has a 9 to 1 compression ratio.  The cylinder volume at the bottom of stroke is nine times more than when the piston is at top of stroke.
(Formula is: swept volume + compressed volume to Compressed volume.)

The piston itself displaces 136cc during its travel.  This means the final compressed volume is about 15 cc for 9 to one comp. ratio.  If your tester adds 10cc at the spark plughole, you reduced the comp ratio to about 6 to 1.
There is a FAQ entry to explain this.

If this can't be understood clearly, I'd recommend using a leak down tester instead of a simple compression tester.

Cheers,

[Kingscorpion]

Should of thought of that! Synthetic oil!
Yes I have semi synth in it which would account for the smell.
From all I have seen theres clearly oil coming up the bore. And my only clear memory of an oil burning engine is from way back when a VW bus blew a gasket producing clouds of blue smoke and a smell like a chip pan fire (french fries) 

That must be it  -synthetic oil burning due to rings/seals problems.

OK back to the rebuilding.

Thanks for the copious and informed advice folks!! Much Appreciated!!!

[Hush]

"Until your finger is injested" love that line Two Tired.

[Kingscorpion]

Ok  - heres the news...

Honed the bores with a three legged wetstone kit on a speed controllable had drill. Very easy to get a nice cross hatch with just a few strokes of this and minimal spring pressure required.
Rebuilt the head with new stem seals and noticed quite a build up of hard residue behind three of the exhaust valves. Quite difficult to scrape this stuff off and I suspect its partly what is causing the sulphur/cordite smell. Guess its been preventing the valves closing so I lapped the valves gently to get a good fit.
Have to say it was difficult to find a valve spring compressor to fit the tight clearance of the head.  (another one for the collection)
Anyway after all the above it started first time and runs perfectly with absolutely NO SMOKE!
First time I have really heard the bike running properly and probably all due to it sitting in a the original owners home being started and run weekly but never ridden until he got too old to do that! The broken ring I suspect occurred when I first started the bike after its long time laid up (so long in fact as to reduce the remaining petrol in the tank and carbs to red coloured varnish/gum -that smelled like old paint!
All looks good now and the compression tester is right back up there at 160psi!.

[Hush]

Nice, seems the valves were your stinky problem.

[Blackandsilver]

I had that problem exactly once. Looked like the bike was running on water the exhaust was white and really weird smelling. The top piston rings had been installed upside down. Glad you got yours going!


Win some lose some, it's all the same to me.

[trueblue]

Glad it's running well, now to put some miles on it

[dave500]

yeah you think you had trouble?my wife thinks i smell strange!dont be afraid to up the rpm,itll keep those valves clean seriously,people that have an old bike or car and fire it up now and again over years can actually do more harm than good,with cold running and incomplete combustion deposits etc,it results in acids in the oil and exhaust system moisture.

[Kingscorpion]

Thanks all  - Its been an experience but all the symptoms add up - smell, moisture,smoke etc. Definately one to note. The ring order is vital. Lesson learned - dont just duplicate what you find in the engine!

Kind of weird though that the rings in what appears to be an untouched motor with less than 2k on the clock were installed wrongly.
Its obvious when you think about it  - the thicker cast iron middle ring is a heatsink/buffer/seal between the compression ring and the oil scraper. I guess that installed in the wrong order there is a good possibility of igniting an oil mist in the cylinder. Hence the smoke etc.
So to recap the CORRECT ring order on a CB500/4 redone with NPR rings is:
Top: Chrome edged ring with R mark uppermost
Middle: Black cast iron ring with R mark uppermost
Bottom: 3 piece oil scraper ring

Now I recall from other posts that the CB500/4 K0 would originally have had a one piece oil ring? Can anyone confirm this?
If so would indicate that someone had been in my engine previously and changed (badly) the rings!!!

Alls sweet now apart from the brake light stops working when the headlight is switched on . ......

[trueblue]

Don't assume that the number on the clock is original, either that or it could be 102k.