[Black fingernail]

Over the last year or so, my nice weather daily ride to work and general runabout, has been my iron barrel Bullet.
After a couple of teething problems, easily sorted, she has been very well behaved, never missing a beat, even starting first kick (when no-one is watching!). until one fateful morning.
The previous evening we got home from work as usual without anything amiss.
Next morning, she started first kick, by the time I had put on my gloves, she stalled, I tried the kick start again, NO COMPRESSION! I checked the tappets, all good, I jiggled with the de-compressor, even removed it and replaced it with a spark plug, no difference, I knelt down and stuck my ear to the inlet and exhaust tracts, couldn't hear anything untoward.
So I went to work in the car!
I looked down the plug hole with my trusty borescope, expecting the piston to be damaged somehow, all looked ok. So, without further ado, off with her head!!
I haven't touched the engine at all while I have owned her, except for general servicing, so I was quite surprised to find just about all the fasteners were not much more than finger tight! I recon I could have stripped the head off with just a pair of pliers! washers were haphazard, two fitted here and there, none elsewhere, no washers of any kind on the oil pipe banjo's, yet, there were no leaks!
The head gasket is brittle and red, I think that is where the compression has gone, there is a fair bit of carbon on the piston, but the head is quite clear, apart from a brownish coating, the bore is perfect, but glassy.
I haven't removed the valves yet.
I'll glaze bust it and fit a new piston, valves, springs, etc. all new gaskets and washers in the correct place, and tighten things correctly.
While I am waiting for the parts to arrive, I will change the gearbox sprocket for an 18 tooth and see if there is room for an 'o' ring chain.
I just find it unusual to just stop without any noticeable symptoms, so suddenly, no lack of power, no 'wheezing', no oil leaks.
I wonder if it was something I said!!

[DavidGraves]

Howdy

Define what you mean by no compression ?

Does the piston go up and down when you kick it ?

Have you tried bump starting it on a hill ?

Good luck with it.

[tooseevee]

           

Howdy

Define what you mean by no compression ?
Does the piston go up and down when you kick it ?
Have you tried bump starting it on a hill ?
Good luck with it.

         If the piston wasn't going up and down there would probably have been a noise to end all noises just before the engine wouldn't restart because the piston wasn't going up and down - any longer 

[Black fingernail]

Howdy

Define what you mean by no compression ?

Does the piston go up and down when you kick it ?

Have you tried bump starting it on a hill ?

Good luck with it.

Hello, to you!
For an engine to run, you need three things, fuel/air mix, a good spark at the right time, and reasonable compression.
Compression is the pressure created in the cylinder by the piston rising from b.t.c. with both valves closed and compressing this volume into the small cavity in the cylinder head to create an explosive mixture for the spark plug to ignite.
The problem with my engine was, this pressure was escaping from the cylinder, the kick starter could be pumped up and down by hand with very little resistance.
The piston does go up and down.
I could have put it in 3rd gear and walked along with it with little effort, so bump starting wouldn't have worked.
The head is off now, if I get time tomorrow I will remove the cylinder and examine the piston, I have left the cylinder head inverted with the combustion chamber full of diesel fuel to see if the valves leak, this is just out of interest, as they are getting replaced anyway together with the springs.
I'll report back when I have anything.

[Black fingernail]

           
         If the piston wasn't going up and down there would probably have been a noise to end all noises just before the engine wouldn't restart because the piston wasn't going up and down - any longer 

Not to mention a bit of an oil leak!!

[Paul W]

I’m not too surprised that the compression loss was sudden. Having worked on a whole range of engines, I’ve often found one where all the head fastenings are undone but the joint between the head and the cylinder/block remains stuck fast and takes quite some effort to break apart.

If all the fastenings gradually loosened off due to vibration, the joint might remain intact for a while, but suddenly give. It doesn’t take much of a leak to cause major compression loss.

[DavidGraves]

Yup...no insult meant there...hope none taken....

Its just that words are all we have on a web forum.

Broken ring ? Burned valve ?

Still good luck with it.

David Graves

[AzCal Retred]

Black Fingernail - In my Snidal book on about page 89 in the "Engine Work" section, he recommends NOT deglazing and use of cast iron rings. Snidal says cast iron seats perfectly well on a used bore, and the deglazing process just unnecessarily opens up piston to cylinder clearances.

Probably like you, I was raised on Japanese machinery with steel rings, and Snidal concurs with deglazing for  steel rings. I'm guessing that in the dim mists of time, the properties of cast iron were well known, and as most engines came apart for maintenance every 8,000 - 12,000 miles anyway, the cast iron rings were treated as normal wear items.

This is a new concept for me, as in my experience a Japanese engine runs 50,000 - 100,000 on all original internal bits. I'm speculating that in the 1940's the paradigm was completely different. Brittle, fast wearing rings were considered a benefit as they allowed for easier rebuilds and reduced piston wear.

So on my machine's upcoming top end I'm planning on dropping in some cast rings, verifying the end gap at 0.015 - 0.020, and seeing if this plays out. As you pointed out, the top end is easy enough to pop off if the rings won't bed in and seal on a used bore. If they work as Snidal says, your engine clearances stay tighter with no additional cost or effort.

It would be good here for Bullet Whisperer or Adrian or Ace to weigh in, as I know they've probably taken a lot of ancient Brit equipment apart. I just have a point source of info from the Snidal book, But I haven't had it steer me wrong yet. I'm OK with old tech that works. My Bullets are low compression, low HP machines, so a good test bed for 1940's maintenance practices. - ACR -

Paul W - thanks for that heads up on yet another failure mechanism. It wouldn't have occurred to me that the gaskets & general crud/shellac/carbon could brittly bond the head to the barrel enough to run, but at 6:1 CR it doesn't take much to hold fast, especially on a stock motor that probably doesn't get thrashed. BF found loose fasteners, consistent with your concept. I'll keep it in mind when investigating future failures! - ACR -

[Adrian II]

Last time I had sudden compression loss was on a BSA B40 where the piston holed.

I wouldn't have thought the rings would fail immediately, did something get stuck under one of the valves and stay stuck to the valve face or its seat?

A.

[cyrusb]

I’m not too surprised that the compression loss was sudden. Having worked on a whole range of engines, I’ve often found one where all the head fastenings are undone but the joint between the head and the cylinder/block remains stuck fast and takes quite some effort to break apart.

If all the fastenings gradually loosened off due to vibration, the joint might remain intact for a while, but suddenly give. It doesn’t take much of a leak to cause major compression loss.

My money is on this prognosis

[Black fingernail]

Yup...no insult meant there...hope none taken....
Its just that words are all we have on a web forum.
Broken ring ? Burned valve ?
Still good luck with it.
David Graves

No, I agree with you, we need clarity, and different people (and countries) use different words for the same thing, or the same words for different things, (are you confused yet?)

[Black fingernail]

I’m not too surprised that the compression loss was sudden. Having worked on a whole range of engines, I’ve often found one where all the head fastenings are undone but the joint between the head and the cylinder/block remains stuck fast and takes quite some effort to break apart.

If all the fastenings gradually loosened off due to vibration, the joint might remain intact for a while, but suddenly give. It doesn’t take much of a leak to cause major compression loss.

I think you are correct.
I have pulled the cylinder barrel off and examined the bore carefully. The bore is perfect with no scoring, bur highly polished and glazed.
The piston has a crust of carbon and soot on the crown, but is in good condition, with a little wear on the sides 90% to the gudgeon pin, (wrist pin). the rings are intact, but a little worn, but not worn out.
The diesel fuel I left overnight in the cylinder head combustion chamber, is still there, so the valves are not leaking.
This top end has been stripped before and has been put back not very well. all the gaskets are old and have been re-used using silicone, the paper thin cylinder base gasket has sections missing, one of the rocker cover gaskets (a black one) is brittle, the other soft and mushy, (a green one).
The face around the stepped cylinder head joint on the cylinder head, is stained brown by the escaping exhaust gasses, so the head gasket must have been leaking a bit for a while, unsurprisingly really, the copper gasket is really springy and hard, with a red colour with brown marks indicating the blow by.
All the joint faces have a slightly lumpy coating of a brown varnish type compound, easily removed with a scotch brite pad, leaving very good gasket faces.

[AzCal Retred]

Excellent & descriptive observation reporting! Looks like with some clean-up and fresh gaskets & you'll soon be back on the road. - ACR -

[Black fingernail]

AzCal Retired.
Yes, I have read the Snidal manual regarding the glazing, I agree in some ways, but disagree in others.
I have worked on all manner of engines, Marine, Locomotive, Automotive, for too many years.
Glazing, is created by carbon filling up the light scoring left by the honing process, and being polished by the rings on an engine that is lightly loaded, the carbon build up is not even, this causes uneven wear on the piston rings. This happens mostly on marine two strokes and large diesels that are run under light load for prolonged periods.
I don't think glazing is a problem on high speed Japanese multi's. Our engines however, are mostly lightly loaded, and are very oily, they don't even have valve stem oil seals, and are low revving.
The honing marks are ideal for carrying oil and providing a slightly abrasive surface to 'bed in' new piston rings.
Distinguishing between glazing and wear is quite forensic, so I normally look at the overall engine and how it is used and 'guestimate' weather or not to 'bust' the glaze, usually I do, just to be sure.
I hope I haven't opened a can of worms.

[AzCal Retred]

Black Fingernail - I certainly agree that "de-glazing" provides a better break in surface, and admire your clear, concise description of the mechanism behind the causes of glazing.

I have 2 sets of cheap stock size cast iron rings, just in case I ham-fistedly break one installing on the piston. I'm just really curious to see how the bed-in process plays out on an untouched worn surface. The compression gauge should tell the tale, and hopefully the oil consumption will decrease from 1 Qt./ 500 miles! I even have another NOS 84mm piston I got years back from CMW if I end up deglazing and have the clearances on the current piston open up excessively. I'd probably go back in with steel rings if I installed a new piston on a deglazed cylinder.

Hopefully I won't find a "ridge" at the top of the cylinder, but a good place to use my hoary old Western-Auto "ridge-reamer" if I do. Wouldn't want to crush-off a ring land on a new piston because a new ring hammered into an old ridge!

Thanks for the insights - ACR -

[ace.cafe]

IF the bore and rings are the issue, I recommend going +.010" bore and new +.010" piston/rings.

Let's face it, the OEM piston is a piece of crap, and so are the rings. It's a good opportunity to get that stuff out of there, put a fresh bore/hone on it to get the correct clearance, and bed in the fresh rings. There is no good reason to retain that OEM junk. Believe me.

[Black fingernail]

IF the bore and rings are the issue, I recommend going +.010" bore and new +.010" piston/rings.

Let's face it, the OEM piston is a piece of crap, and so are the rings. It's a good opportunity to get that stuff out of there, put a fresh bore/hone on it to get the correct clearance, and bed in the fresh rings. There is no good reason to retain that OEM junk. Believe me.

I couldn't agree more, my bore is ok, I'll be staying standard, but a forged piston is going in, with a light hone, new valves & springs just to make sure, and I'll put it back together carefully with new gaskets, washers, etc.
I noticed that the rocker feed pipe has had a straightened out kink! so that is being replaced also.
I do not understand why the oil control ring groove has been sliced in such a manner on the OEM piston, would it not have been better to drill it like everybody else?
I am not in a great hurry to get her back on the road, I am taking my time, so I am unashamedly taking advantage of a good friend of mine who likes to polish aluminium casings, he has just done the rocker covers, and has taken away the cylinder head, I'm intrigued as to how that pans out! When the head is back, I'll give him the timing cover!

[Adrian II]

It's quite common to tart up the cylinder head casting by carefully removing all the casting flash and generally tidying up the fins, then polishing the fin edges, ideally after the head has been vapor/vapour blasted. Once that has been done, you'll need an alloy barrel finished to match. 

A.

[ace.cafe]

Just be careful with clearance on that forged piston. It needs noticeably more bore clearance than the cast piston did.

[Adrian II]

That was certainly true with the Accralite high-compression pistons a few years ago.

A.

[AzCal Retred]

Anodizing comes in a wide variety of colours, if you're going for flash...shouldn't adversely affect heat transfer either. 

[Black fingernail]

It's quite common to tart up the cylinder head casting by carefully removing all the casting flash and generally tidying up the fins, then polishing the fin edges, ideally after the head has been vapor/vapour blasted. Once that has been done, you'll need an alloy barrel finished to match. 

A.

I'll just leave him to it, lucky for me, he is very OCD!

[Black fingernail]

Just be careful with clearance on that forged piston. It needs noticeably more bore clearance than the cast piston did.

Thanks for that, I'll measure it carefully, how much clearance do you recommend?

[Adrian II]

Check with Mr H, I think they had to issue revised instructions!

I'm not sure anodizing works that well on cast alloy.

A.

[ace.cafe]

Thanks for that, I'll measure it carefully, how much clearance do you recommend?

It depends on the piston, but generally they need at least .005" but not more than .006". The maker should give specs, but sometimes those specs are for water cooled applications.
Beware of any forged piston specs calling for less than .004" clearance.

It comes down to how dense the forging is, and how much material is located on the critical expansion areas to soak up heat and expand.
For our Ace piston forged from 2618 and plenty of lightening machining, we could do .005" if we were very careful about state of tuning and controlled break in.
However, at .006" we might get some piston slap, and at .0045" it might seize,  so it is a tight window for clearance.

[Black fingernail]

Just an update.
The piston and rings are fitted, nicely honed cylinder ( to suit piston clearance), fitted with new base gasket.
I'm just waiting for Big Al. to finish doing whatever he is doing to the cylinder head, he has informed me that one of the old  valves was not seated to the collets very well, It seems he is cleaning up the ports as well, I'll find out on Monday.
Now the cylinder is sorted and I am awaiting parts, I'll get the primary casing off ready for Al. to polish them when he brings the cylinder head back. I have got an 18 tooth sprocket ready, and a foot of 'o' ring chain (off cut from work), so I can see if a full 'o' ring chain will fit.
I'll take some pics as things go on.

[cyrusb]

Not so sure the Oring chain will clear the inner primary cover. The master link pins contact the inner primary with a standard chain.Thats why my stock machine had the link installed the "hard way" with the clip on the inside.  But with a Bullet, who knows, you may have the room. Also a 19t drive will eliminate the half link.