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Bedding/Lapping Piston Rings.

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31K views 25 replies 16 participants last post by  Tritn Thrashr  
M
#1 · (Edited)
Here's the original method as it was described to me.No doubt there are alternatives.I've used this and it does work well,and gives better results than any conventional run-in procedure.I currently use a slightly different procedure.

After you hone and re-ring,but before you fit the head:
Mix BON AMI (original 1886 formula powder cleaner [yellow,not metallic gold container];the more modern "powder cleanser" formula has sweet smelling stuff and plant oils and does not have "1886 formula" on the container ) with thin oil,to make it like toothpase.
With the pistons at BDC,cover the bores with this mixture.
Rotate the engine 2 or 3 times and add more mixture.
Do this until you've done 40 revolutions.At about 30 revolutions you'll see the mixture turn grey.
Do not add any more mixture.
Rotate the engine 10 more turns,wiping off as much mixture as you can.

#Fit the head and start the engine.No slow idling,ride the bike.Alternate between heavy load (for a few seconds),and closed throttle.
After about 20 minutes,do an oil change.This is mostly to get out the metal bedded from the rings,not so much for the BON AMI.
- - - - - - - - - - - - - - - - - - - - - - -

Thesedays,I lap the rings before I fit the barrel:
Mix BON AMI with liquid detergent.

*Check the ring gaps before you fit the rings on the piston.It's usually a good idea to have 30% bigger ring gap on the 2nd ring,compared to the top ring gap (say 0.003"-0.004" bigger).It helps the top ring seal,and reduces oil consumption.

Fit the rings and piston into the bore with a spare conrod (or a stick with a hole) attached to the piston.
Cover the bore above the piston with this mixture.
Push the piston up and down the bore using slight rotation on each stroke.
Add more mixture every 2-3 up/down cycles.
After about 45 up/down cycles,pull the piston out and check ring contact.It should show continuous contact around the circumference,not necessarily across the full width.

*Do not remove the rings from the piston.
Rinse the piston/rings with water and blow dry.
Rinse and dry the barrel.

*Coat the barrel with WD40 or ATF.Wipe most of it off (as much as you can).
Put one drop of oil on each side of the piston skirts,none on the rings.
Assemble and run as previous method.
 
#4 ·
Pete,

Good of you to set this out in clear terms for us. I had asked around some old timers but could not get a clear answer on the procedure.

Yes, I can see this method being worth the effort as it reduces the uncertainty owners will have about ring seal.

What happened to the days when rings failed to seal and we inroduced some lovely Bon-Ami via the carbies for an instant bed in (just joking!!)

Many thanks Pete. RR
 
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M
#5 ·
I put all the rings in place,and lap them all at once.They don't come off the piston again;they just get a wash-off.
I've heard that sodium bicarbonate works too.I haven't tried it.

BON AMI down the carburettor was used by GM and Land Rover,to reduce oil consumption.That's still a bit scary.
 
D
#6 ·
As a kid i remember holding the funnel while a dodgy uncle added a tablespoon of brasso metal polish down the sparkplug holes of an incredibly smokey humber 80. It completely stopped the smoking for exactly 45 miles and then it was ten times worse but he had managed to sell it before the smoking restarted
 
J
#7 ·
Mr.Pete said:
Here's the original method as it was described to me.No doubt there are alternatives.I've used this and it does work well,and gives better results than any conventional run-in procedure.I currently use a slightly different procedure.

After you hone and re-ring,but before you fit the head:
Mix BON AMI (original 1886 formula powder cleaner [yellow,not metallic gold container];the more modern "powder cleanser" formula has sweet smelling stuff and plant oils and does not have "1886 formula" on the container ) with thin oil,to make it like toothpase.
With the pistons at BDC,cover the bores with this mixture.
Rotate the engine 2 or 3 times and add more mixture.
Do this until you've done 40 revolutions.At about 30 revolutions you'll see the mixture turn grey.
Do not add any more mixture.
Rotate the engine 10 more turns,wiping off as much mixture as you can.
Fit the head and start the engine.No slow idling,ride the bike.Alternate between heavy load (for a few seconds),and closed throttle.
After about 20 minutes,do an oil change.This is mostly to get out the metal bedded from the rings,not so much for the BON AMI.

Thesedays,I lap the rings before I fit the barrel:
Mix BON AMI with liquid detergent.
Fit the rings and piston into the bore with a spare conrod (or a stick with a hole) attached to the piston.
Cover the bore above the piston with this mixture.
Push the piston up and down the bore using slight rotation on each stroke.
Add more mixture every 2-3 up/down cycles.
After about 45 up/down cycles,pull the piston out and check ring contact.It should show continuous contact around the circumference,not necessarily across the full width.
Do not remove the rings from the piston.
Rinse the piston/rings with water and blow dry.
Rinse and dry the barrel.
Coat the barrel with WD40 or ATF.Wipe most of it off (as much as you can).
Put one drop of oil on each side of the piston skirts,none on the rings.
Assemble and run as previous method.
Click to expand...

hi mr pete , do you know were id get the bon ami from ,i live in australia and i cant find it any were . can i use ajax in power form , is this the same stuff . thank again for the help.ps i have reassembled the head with the locktite 567 around the base of the giudes ( so expensive $33 ) anyway i also installed the orings under the colits . hope it all works lol i check the valves with smoke paper like you said and it seems fine all the best jack
 
M
#8 ·
Ajax won't work.It did once,a long time ago.They changed the formula to "no-scratch" about 20 years ago,and it became useless.
I bought a life-time supply supply of BON AMI,in case that changed too.

You can still order it online.The main ingredients are feldspar,limestone and sodium bicarbonate.I've heard that a little bicarbonate powder can fix a glazed bore.

You need something mildly abrasive,but water-soluble so you can wash it off.You could try a mixture of old-fahioned toothpaste and sodium bicarbonate and some liquid detergent,but I don't know if it's abrasive enough.If the mixture doesn't turn grey at about 30 strokes,it's probably not abrasive enough.Check the ring surface to see if it has bedded in.You can tell by the shiny appearance.
 
#10 ·
Years ago my buddy Lance was on a road trip with several friends. All were riding Brit bikes, which were relatively new at the time. One of the riders was on a bike with a recently rebuilt engind and it was smoking a bit. They figured it would lap in on the ride. It did not and continued to smoke. They stopped at a Brit dealer in Canada and expected to do a quick top end on the engine before heading back on their route. The dealer wanted to try Bon Ami (Good Friend, in French) before tearing into the engine. He put about a teaspoon or so of Bon Ami into each carb with the engine running. Lance said it quit smoking almost instantly. I'm sure instant in this case is relative, but quickly, nonetheless. The continued on their way and the bike ran fine and never did get torn down.

I would agree that the thought of the Bon Ami washing down the cylinders at some point and getting into the sump is a bit unnerving, but then again, it can't be any worse than carbon.

Thanks for posting the procedure, Mr. Pete. I'll be cutting and pasting this into my Tech Tips folder. It would probably be wise to post this in the Tips and Tricks section.

regards,
Rob
 
J
#12 ·
hi guys i was telling a fello biker about the bon ami mr pete was talking about the other night and to my surprize he siad he used to do it all the time on the old bikes and cars but he too would add a teaspoon in to the carbs while holding the revS at about 4 thousand revs. he said it worked every time , hes a old guy and said you cant get it in aussie land anymore.but ive ordered on ebay , from the states. SO THERE IS A MAGIC POWDER THAT REALLY FIXES THE BEST OF THE BRITISH
 
#14 ·
Mr Pete, any issues to watch out for with this procedure? I followed it per direction here but now have a leaky cylinder. I took it apart and there's some bumps/irregularities at the TDC point. this was a fresh rebore, new pistons,rings, from a respected machine shop. something has happened. could I have done something wrong following these directions? It seemed pretty simple. I cleaned off as much of the mixture as I was able to following the treatment but if there was a little mixture left behind could it create damage? i would think it would just burn off?
 
M
#15 ·
I've always found it worked really well.I use the liquid detergent instead of oil,because it's easier to wash off.It's best if you don't remove the rings from the piston,once they're bedded.Just wash off what you can.

I've known people to not even strip the engine to wash it off,and just wipe off as much as possible above the piston.They do an oil change shortly afterward,and everything's OK.
Your problem could be in the barrel,if the cylinder surface looks uneven.It might need a re-hone to straighten it up.
 
#16 ·
thanks. I found the culprit. It was me! I got some of the crap into the bolt holes and didn't clean properly. Then when I torqued down created a hydraulic lock. which bowed out the cylinder slightly by the bolt-holes.

To anyone doing this: keep your bolt-holes squeaky clean. then, when its time to put the head on dip your bolts in a little oil and let it run off.

You see, I learn by breaking things. Anyway - Rabers has it again and thinks he can re-hone to clean up my mess. Fingers crossed! then I'll be back to break-in again.
 
M
#17 ·
Pete, I'm new here BUT what a brilliant bit of a technical tip your post is! I have been tinkering with Triumphs for a good 30 years or so and am pleasantly surprised to note that I do not know everything and can still learn a lot about tinkering with engines. By eck I'm glad I joined this motly lot of Triumph owners :)
 
#18 ·
I think I'm going to do something with Bon Ami.

After a bore hone and new pistons, I have good compression (185 psi) on both cylinders, but the timing side is getting oil in the combustion chamber. The backs of both valve heads are dry; piston crown is oily.

No visible smoke, unless I let it idle for some time and then rev up.

I'll lift the barrels, because I kind of suspected a partial seizure, which may have stuck the oil ring. I'm the World's worst mechanic and one carb needle wasn't in the notch I thought it was.
 
#19 ·
Triton Thrasher said:
No visible smoke, unless I let it idle for some time and then rev up.
Click to expand...
This is very symptomatic of oil being sucked down the valve stem guide when manifold vacuum is high (at idle). You'll see cars idling at he lights, then let go a pile of smoke, which quickly settles as the engine increases RPM and manifold vacuum is subsequently reduced.

By all means try the Bon Ami (note Pete's rider about getting the old stuff). If you've lost an oil ring, or the scraper has not bedded, then you might expect to see oil leaking from the silencer.

I recall when I was a youngster, larrikins would claim to induct Bon Ami straight into the engine via the carby. Now, that would bed the rings, but the mind boggles about what else it would do. :) RR
 
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#20 ·
I do have a packet of the old "never scratched yet" Bon Ami. It's an unknown product in the UK, but found some reasonably priced on the internet. Also found madly expensive examples!

Don't worry- I'm wary of jumping to conclusions as to causes of the smoking and coking.

I'll dismantle the top end, because if there's a stuck ring or an upside down ring, the powder wont fix that. Also will get a proper look at the ports, for leaky guides.
Iron headed Pre-units are good for tearing down and sticking back together.
 
D
#25 ·
Triton thrash’s.
thanks, but that link just gives the new version, which apparently is not what we need.....and it’s for 5 cans, and I only want one.
it seems like I need to keep looking,

thanks again TT
 
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