Camchain and tensioner seen up close in a cutaway bike engine

Home Repair And Restoration

To Hone - Or Not To Hone (Or Deglaze)

Job Date - 7/5/15

By Ren Withnell

Sharon's Keeway has been burning a little oil. At 19,000 miles on a 125 this may or may not be expected, that is a subject for another discussion. Crankcase breather problems can cause oil consumption so we bypassed that with a crankcase filter. This made no difference at all. Personally as the engine was working just fine and dandy I suggested Sharon leave it alone, just make sure she's got a litre of oil with her if we're heading off into the wilderness for a week. However she decided that we should put some shiny new rings around the piston.

Rings are cheap enough. Gaskets are cheap enough. We also had a very very kind offer from a friendly motorcycle shop to run his honing tool around inside the barrel which would deglaze the bore. This lead to a massive amount of discussion and research by both Sharon and myself into the merits, reasoning and purpose of such an action.

Now before we carry on let me make one thing clear. We HAVE NOT rebored the barrel. While I do not have access to super duper mega accurate measuring tools to assess the ovality and squareness of the barrel a simple visual inspection showed no signs of scoring, wear, ridges, gouges or damage of any kind. There were no peculiar sounds from the motor at all. As such I was happy to simply install a new set of rings, thinking that perhaps the oil control rings in particular were worn. All we have done is replace the rings with new ones.

Hone or Deglaze? These 2 terms are used interchangeably it seems. Strictly speaking honing is done after a barrel has been rebored to remove the reboring ridges and provide a much more friendly surface for the new piston rings to bed into. Deglazing - or even de-polishing - is simply a very VERY light hone to remove the now smooth and shiny surface of a barrel that has been in use for some time. 

Honing or Deglazing toolA basic DIY hone or deglaze tool.

Barrel or Bore or Cylinder? For the novice mechanic these things mean pretty much the same thing. That said if you rebore a barrel/cylinder/bore a machine is used to cut out material to make a larger barrel for a larger piston. If you rebarrel an engine that would imply you have new barrel/cylinder/bore fitted. Semantics - just make sure whoever you talk to that you are both entirely clear what you are talking about otherwise things could get messy. English - as clear as mud.

The cylinder or barrel or bore on Sharon's KeewayThis is the cylinder or barrel or bore...just make sure everyone you talk to agrees!

So - should we get the barrel deglazed? 

The received wisdom is thus... When fitting new piston rings thou shalt deglaze (or hone) - the bore. 

HOWEVER! While 80-90% of the internet's forum posts all agree that new rings = deglaze we kept on coming across anecdotal stories both for and against. The stories all run something like this... 
"I fitted new rings to my '87 Chevy and did not deglaze, now the darn thing drinks more oil than petrol..." 
"I fitted new rings to my '87 Chevy and did not deglaze, I ain't used a drop of oil now for 300,000 miles..." 
"I fitted new rings to my '87 Chevy and got it deglazed, now the darn thing drinks more oil than petrol..." 
"I fitted new rings to my '87 Chevy and got it deglazed, I ain't used a drop of oil now for 300,000 miles.." 

I'm sure anyone who's used the internet for advice on mechanical matters has come across similar situations. This to myself implies there is no hard and fast rule. It all depends on the ability of the mechanic. It all depends on the tools and parts used. It all depends on the condition of the engine before and after the work. It all depends on how the car is driven. The only fact is there are too many factors to build a solid and scientific case either for or against.

Then we came across the following web page CAREFUL WITH THAT HONE, EUGENE! This chap suggests some science in favour of not deglazing and much of it makes sense. Why make the bore bigger, even if it is only by a tiny teeny weeny amount? Why risk contaminating the oil with honing material, no matter how well you clean afterwards? Why put the piston rings and barrel through another running in process? 

Now I am not telling you what this gentleman says is true. He does offer research to back up his arguments but then there is no link to the SAE's official website to confirm this. And yet I can see the logic in his arguments.

After much more discussion Sharon postulated the following logic. "We can fit the new rings without a deglaze. If all is well then excellent. If not while it will be a major pain in the backside we can always get it deglazed later on. If we have it deglazed now we can't get it - ahem - un-de-glazed." I was and remain staggered at her perfectly clear logic and thinking in the face of a tidal wave of conflicting opinions.

At the time of writing the engine is back together and has been test fired with success. The exhaust and several other parts will be refitted next weekend and the bike should be shaken down to ensure it is safe. Then we will begin the process of monitoring oil consumption. I have warned Sharon that it could take a thousand miles for the new rings to settle in before consumption falls. Please watch this space and feel free to add your tuppence to the melee. We are not experts and we are both completely open to your thoughts, opinions and anecdotes.

Reader's Comments

Daf said :-
In the past, and admittedly working on larger diesel engines, I've lightly roughened up a cylinder bore with *Very* fine wet and dry rubbed lightly round the bore in a similar way to a cylinder honing tool would move. Literally only a couple of movements in each location. Dunno if it makes any difference, but I was always told it helped the new rings 'stick' better.

As for honing a cylinder properly with a honing tool - I wouldn't bother unless there's signs of ovality or a lip.

Looking forward to an update on this!
08/02/2016 22:37:58 UTC
Ren - The Ed said :-
Cheers Daf. I read tales of people using Scotch pads or even scouring pads! Yes most agree the idea of deglazing is to provide a keyed surface for the new rings to bed into, as you say 'stick' to. The polished surface of a used bore may be too smooth to allow the rings to wear to fit.

I agree totally that if there is ANY signs of wear such as scoring, a lip at the top of the bore or out-of-round then a hone is a minimum, in fact probably much more would be required.
09/02/2016 07:19:03 UTC
Daf said :-
Agreed there Ren. I actually would say that older engines would get glazed, and for three reasons that are no longer with us. One being leaded fuel leaving a coating of lead on the cylinder bore, the other reason being that engines are now a lot more oil tight than they used to be from the moment they leave the factory onwards, and lastly, that the quality of petrol (of whatever variety) is very much better than it used to be!
14/02/2016 18:10:23 UTC
Ren - The Ed said :-
Yes that makes sense. Yesterday's received wisdom may no longer apply with new oils, fuels, metallurgy, engineering and probably many other factors.

Well the bike has been out on the road and we covered 75 miles yesterday. We discussed "running in". Of course the internet provided many various opinions, we decided she should ride it the same as she's always ridden it.

We could not see any visible smoke from the exhaust but then we never did before. Only time will tell if we have been successful.

Thanks Daf.
15/02/2016 08:15:38 UTC
Pegmonkey said :-
With a well worn engine.. and Without the proper measuring tools, it's just a bit of guess work about what will work best. Several things happen when a cylinder wears. Since the connecting rod and piston exert centripetal forces against the cylinder wall fore and aft, as opposed to side to side, you'll get more wear fore and aft resulting in an oval shaped bore. Next, the piston rings will wear the bore right up to the top and bottom edge of their travel. This, over time, will create a sharp edge often referred to as a ridge. Judging by the picture, you did indeed have a ridge. There is a ridge reamer tool that will get rid of the ridge. The danger of the ridge is, that the new rings will smack into the sharp edge since they will generally have tighter clearances.. thus exerting pressure on the piston ring lands.. and cracking the piston.

Another wear pattern that occurs is the top part of the bore wearing more than the bottom part of the bore. This results in a conical shaped cylinder with the wider part of the bore being at the top. This is not as much of a problem as an oval bore.

If in doubt.. and lacking proper measurement tools, The best course of action is to hone the crap out of everything, especially the ridge. This will allow for maximum wear in clearances to be taken up. With an air cooled engine, tolerances for clearances are quite liberal. So any looseness should not be a problem.

Now.. having said all that, 19,000 miles is hardly broken in by any means. I'm guessing that any oil consumption problems at that low mileage on such a gently driven 125 (Unless Sharon is living a double life as an underground street racer) were due to inferior oil (not compression) ring tension in the first place. I doubt you had any measurable wear on the cylinder and your ring job will be just fine.

As for break in. Heat cycle is the key. Good and hot run it like you stole it for a very short time. Let it cool. Run it like you stole it. Let it cool. In real world terms, run it full throttle for a few minutes. Run it gentle for 10 to 15. Ram on it again for a few minutes. Gentle for another 10 to 15. No steady state cruising for the first 300 miles or so

This has been an hour with Raymond.. stay tuned next time when I call from another location.
17/03/2016 13:45:50 UTC
Ren - The Ed said :-
So far we've put almost another 1,000 miles on Sharon's bike since the rebuild Pegmonkey. Running in so accurately is difficult as the bike is used as transport and for pleasure. It got heated up in use, and cooled down when we stopped for a bite to eat! We did avoid motorways for the first few hundred miles or so.

There are SO many opinions on what causes premature wear. And SO many opinions on how to run in. In fact there is just SO much different advice that neither of us really knew where to turn. It has been quite bewildering to read and hear such varied advice.
17/03/2016 17:38:28 UTC
Sharon said :-
Pegmonkey ... hmmm a gently driven 125 is not how I would describe my little bikes life. He does indeed sometimes trundle along sheep tracks at a sedate pace which I do indeed adore. However when I am chasing bigger bikes around Scotland or just playing on dual carriageways or faster roads the bike does often get pushed to it near its red line. I am gentle with him I am afraid ... far from it.
17/03/2016 22:50:54 UTC

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