glazed bores?

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Ardenfour

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in the quest to reduce the amount of smoke belching from the exhaust last time my engine ran, I've now got the piston out to check the rings. They certainly look ok, but how to check? Is there a typical ring end gap when in the bore? The bore itself is very shiny - should I 'hone' it, if so how do I do it? Also the valves leaked before I dismantled it. The valves and valve seats have a chrome-like finish, does this mean I can't grind them back in as they're a hard material (stellite)?
I've checked the injector under microscope and see crud in the holes, so should I take it for service or is there a way to clean it myself?
The cylinder bore has a layer of carbon above the piston travel, should I clean this off or leave?
 
You should be able to hire a cylinder hone, make sure you end up with a nice crosshatched finish. Maybe a set of rings would be a good idea, in which case you removethe ridge from the top with a ridge reamer if it is in the metal, or with a scraper if it is carbon only. It could be that your bottom oil control ring is stuck with carbon. Does it move in the ring groove? An engine reconditioner can probably re face the valves and seats, and also offer an opinion on the bore issue. Get the injector done professionally.
 
Unless you are a master with a cylinder hone, get it done profesionally, get him to check for bore wear and ovality at the same time.
New rings will not bed into old polished bores, so if you are fitting new rings, you have to "glaze bust" the bores.
You will have to remove the carbon at the top of the bores if honing.
Ridge reamers are also for profesionals, you can make a right pigs ear of it.
Rings should be checked, in pistons for side gap and bore for end gap, if you dont know what I'm talking about, it might be best to have that done, which should all be in your workshop manual. Valves and seats can be ground, but the guides need checking as well, if they need replacing, the seats/valves will all need doing.
I would also start with everything spotless, caustic soda will get rid of all the old carbon etc.
I would farm out all measuring and machining and do the assembly donkey work your self.
Injectors again leave to the profesionals, unless you have a test bench pressure pump.
These things are just the beggining, you have the bottom end to consider as well.
If you are not a full blown mechanic/engine re-conditioner, this is the way you should go. IMHO
 
The cheapest part of any rebuild is the engineering bit, have it done by the professionals and then assemble the engine yourself (if your capable)
There is a minimum and maximum ring gap but you need specialised equipment to make sure the bores are not oval first.
Most well run engines when stripped will have the appearance of glazed bores, honing is to reduce the wear in period when new or rebuilt.

Good luck and let the forum know what the outcome was?

Tom
 
"honing should only be done by pros"
absolute cobblers a piece of fine emery ran up and down the liner at 45 degrees angles is all that need be done.
 
Just read this post. What a pity people have to always criticise good advice when they dont know their a**e from their elbow. Very sad. I have to say I support what ccscott and little ship have said entirely and Joe has a valid point too. I would ignore the rest although chippies advice is obviously well meant. He may well have the skills to handle the job himself. Frankly if you don't have the background to tackle the engineering, stick to assembly and dissasembly and give the work to a professional. I would also support csscott in his statement that if the top end is like this the main bearings and big ends are also suspect. Either do the whole job properly or do nothing.
 
dear oh dear boatmike
please do divulge why you think the other comments are as you put it "sad"
you obviously have a high opinion of your own knowledge.
i guess you are still of the old school that thinks things such as grinding in valves is the correct thing to do.
 
Before throwing money at it, whether DIY or Pro, you can easily check the state of the bores and rings yourself with a feeler gauge:

Remove the top ring (carefully as they break easily!) and clean reound the top of the bore. Insert the ring in the bore, and measure how wide the gap in the ring is. Makers will give a maximum permissible measurement, known as the 'ring gap'. Next, slide the ring about a third of the way down the bore, and measure how much wider the gap is at this point which is the area of maximum wear. You can also gain some idea of the ovality of the bore by using a feeler gauge between the ring and the bore. You need to rotate the ring and measure several times, unless you are using a new ring which is truly circular. You will find the maximum wear point in the bore is at right angles to the crankshaft.

Armed with these measurements you can decide whether you would get away with new rings, or if you need to rebore.

Incidentally, I have 'emeried' several engines which just needed rings, which have gone on to run happily for many years after. The angle of cut needs to be around 25 - 30 degrees, certainly not as much as 45 for succesful bedding of the new rings. The 'roughening' of the bore is not just to help the new rings to bed in, the cuts also hold extra lubricating oil which helps the rings to bed in and seat properly, and improves the seal during and after the bedding in process, which is why they should not be cut too steep.

If the engine has enjoyed regular oil changes during its life, the bottom end should be perfectly ok even if the bores are quite worn. Checking and measuring bottom ends should really be left to the pros who know what to look for. An experienced eye can quickly detrmine whether the bearing shells are dodgy and if so, why.
 
agree with what oldharry says just one point about the angle of honing
The correct angle for cross hatch lines to intersect is approximately 45 degrees. Too steep an angle promotes oil migration down the cylinder resulting in a thin oil film which can cause ring and cylinder scufflng.

Too flat a cross hatch angle can hold excess oil which conversely causes thicker oil films which the piston rings will ride up on or hydroplane. Excessive oil consumption will result.

to quote my old marine engineering books
 
[ QUOTE ]
i guess you are still of the old school that thinks things such as grinding in valves is the correct thing to do.

[/ QUOTE ]And what would you suggest if the valves are leaking?. If the valve stem and guides are O.K. then why nt lap the valves back in? I mean that is what valve lapping paste is for - isn't it?
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"Artificial intelligence is no match for natural stupidity"
 
im just being pedantic really after boatmikes response, but since you asked, if a valve is ground into its seat with paste, the result is two faces on exactly the same angle making a near perfect seal.

problem is the thermal expansion of the seat and valve are different so when the engine is at operating temp the faces no longer seal like they did when cold, which obviously results in reduced efficiency.

when i was an engineer in the merch we used a system called hunger gear which cuts the face at the manufacturers specified angles.

but like i say i was just being pedantic as we all know that the tried and tested method of griding paste and elbow grease is fine for the average boat engine with there agricultural tolerances, and funnily enough so is using 220 grade emery on the liners
 
good advice from all really. On a lowish performance engine you won't do too much damage. Roll the valves on something like glass to check they are flat before too much work. The emery paper is fine. Lots of cylinder bores are indeed oval - they expand longitudinally to become circular.

The injectors are the main place to start really, and erm, i am not at all sure i wd've taken the head off - just get a man to do the injectors, new airfilters, oil change covers most things on a diesel...
 
getting back to the original post, i completely agree with tcm it sounds like the air filter and possibly injector
 
There may well be a textbook somewhere that says this is wrong but I've used a cheap "glazebuster" on the end of an electric drill on several engines now and it always seems to work. It's just a big "flapwheel" really. It only takes a few seconds to scratch the glaze off the bores.
 
I agree Tyce, unfortunately I think stripping down was quite possibly not necessary. However now its done, he might as well check the state of the rings/bores. Valve problems are highly unlikely in my view given the symptoms described - far more likely the injector needed attention.

I strongly suspect he will put it all back together again, with new rings etc, and find nothing has changed.....

Halcyon - what colour was the smoke? Black, greyish white, or blue? If it was black it was almost certainly an injector or fuelling problem. Ditto greyish white - or maybe even it was steam from a partially blocked or faulty water pump not cooling the exhaust and producing lots of steam. Blue smoke is the only one that really warrants stripping down as it denotes that lube oil is being burnt from getting in to the wrong part of the engine.
 
hullo all, thanks for the replies and advice. I added more info halfway down this thread but it's got lost somewhere. Anyway, the engine is aircooled, 9hp, no head gasket just the mating surfaces. 4 nuts and the head was off, so no great hassle. The valves leaked, cos with the exhaust mainfold off, I'd flung some WD40 and engine oil in to try and prevent corrosion as I wouldn't be running it for a while. I could see bubbles around the valve seat as I turned the engine through a compression stroke. With the valves out, the area of contact with the seat is a bright chrome appearance - is this likely to be an especially hard metal coating, stellite for instance, and grinding the valve might destroy this? There appears to be some very superficial pitting on this area.
The piston, and cylinder bore above the piston stroke is heavily carbonised - should I remove this ring of carbon? Seem to remember that 2 stroke bikes should have it left. The oil ring moves freely, but was quite clogged up with sludgy stuff.
The piston seems a tight fit in the bore and I cant feel any lateral play. The piston was stained a tea colour below the level of the rings if that means anything. Not much play in the valve guides either.
The rocker cover has a plastic disc held in a cage below the breather outlet. This disc is broken in half, also looks as though there should be a spring in the assembly to hold it shut - no spring was fitted. There is a fair amount of pressure from the rocker cover, along with an oil mist so where's it coming from?
The engine has been obsolete for years, I dont have a manual and cant get any spares for it.
The smoke was bluish, if I remember rightly. I was told at the time of purchase (not by the seller) that the engine done this every year and that it cleared aftyer a few runs.
 
Just out of interest how many hours would you expect from a marine engine asuming regular serviced ,oil cahanges etc before needing an overhaul.

I appreciate any estimates must be approximate but wondered if marine engines were following cars in vastly increased longevity.
 
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