Author Topic: Broken piston ring  (Read 4754 times)

0 Members and 1 Guest are viewing this topic.

Offline cj8990

  • Full Member
  • *
  • Posts: 56
Broken piston ring
« on: September 13, 2015, 11:11:50 PM »
So I'm in the middle of a head gasket rebuild and I've found that one of the rings broke.  So now I'm forced to replace the rings which I've never done before.  After some reading online I think I get how it's done but now I'm a bit confused as to what rings to buy and what gap to set them to.  Now I'm assuming my recently acquired (last 6 months or so) 76 cb550 is still at the factory bore but to check that is as simple as measuring the diameter of the cylinder sleeve correct?  And assuming it is at the factory bore than it's as simple as ordering rings and setting them to the factory gap.. so I found these..

http://4into1.com/rik-brand-piston-ring-set-standard-13011-374-000-honda-cb550-1974-1978/

And when I get them I'll just gap them to what it says in the manual.. is one of these necessary or recommended for filing the ring down..

http://www.summitracing.com/parts/sum-906795?seid=srese1&gclid=CPHgwqLi9ccCFY81aQod3S4Nrg

I saw some videos that stressed when filing the ring it must be squared up with the other end and to be careful de-burring so you don't "round" the edge of the ring and create a larger area between the two ends of the rings and so that makes me think I should get one of those too?

Also I don't have a spare piston available to set the ring at the same depth when measuring the end gap so I was wondering if the "bolt method" is fine to work with?

thanks for any help,
-Corey

Offline mrfish2

  • I might be a
  • Hot Shot
  • ***
  • Posts: 679
Re: Broken piston ring
« Reply #1 on: September 14, 2015, 07:02:50 AM »
Search ebay for a cb550 piston ring set, there's a seller on there called CruizinImage who sells big bore kits and piston ring sets. I used their ring set when i had to replace mine and 1000 miles later i still don't have any issues. Their kit is only $40+shipping, you can't beat that price.
1976 CB550K            1979 XS1100
1980 CB650C - Sold

It's a little motor and likes having the tits revved off it.

Offline martin_uk

  • Hot Shot
  • ***
  • Posts: 272
  • CB750F1 CB750K8
Re: Broken piston ring
« Reply #2 on: September 14, 2015, 08:13:00 AM »
If the bores are OK and within limits, you will still need to de glaze the bores with a light hone.

Polished bores will not allow the new rings to bed in.

As a rough guide you can check a ring gap at top and bottom of cylinder bore and note the difference as the bottom of bore does not wear much.

Fitting rings needs care to avoid breakage, I speak from experience  :-[

If you take cylinders to a specialist they can check if pistons are oversize replacements and  the amount of wear and do a light hone.

This is a wise precaution as you dont want to be taking it apart again :) 
CB750F1, CB750K8,  Triumph Street Triple R, AJS 350, Triumph 3TA

Offline 754

  • Really Old Timer ...
  • *******
  • Posts: 29,046
Re: Broken piston ring
« Reply #3 on: September 14, 2015, 09:02:07 AM »
Use you piston to square up the ring, then pull it out again..you are checking the ring by itself.
Maker of the WELDLESS 750 Frame Kit
dodogas99@gmail.com
Kelowna B.C.       Canada

My next bike will be a ..ANFOB.....

It's All part of the ADVENTURE...

73 836cc.. Green, had it for 3 decades!!
Lost quite a few CB 750's along the way

Offline cj8990

  • Full Member
  • *
  • Posts: 56
Re: Broken piston ring
« Reply #4 on: September 14, 2015, 11:50:06 AM »
Search ebay for a cb550 piston ring set, there's a seller on there called CruizinImage who sells big bore kits and piston ring sets. I used their ring set when i had to replace mine and 1000 miles later i still don't have any issues. Their kit is only $40+shipping, you can't beat that price.

Much better price on those.. thanks!

If the bores are OK and within limits, you will still need to de glaze the bores with a light hone.

Polished bores will not allow the new rings to bed in.

As a rough guide you can check a ring gap at top and bottom of cylinder bore and note the difference as the bottom of bore does not wear much.

Fitting rings needs care to avoid breakage, I speak from experience  :-[

If you take cylinders to a specialist they can check if pistons are oversize replacements and  the amount of wear and do a light hone.

This is a wise precaution as you dont want to be taking it apart again :) 

So just simply replacing the rings isn't an option.. the cylinders need to be honed to help break in the rings?..

After some googling my understanding of honing is just cleaning up the inside of the cylinder and putting a cross-hatched pattern going up and down the cylinder to help retain oil for breaking in the ring??  After running the tool up and down the cylinder nothing fancy is required and I can then continue with gapping and filing the ring and reassemble the engine?  That is of course if the cylinders aren't egg shaped or tapered when measured with a bore gauge, in which case machining is required and there would be no point in just replacing the rings without doing so?

Sorry for the list of questions but does all this sound correct or am I missing something?  It seems this is rapidly turning from simple head gasket job to complete rebuild and, although I've never gone this far before, I'm not one to have someone else finish it for me.

Use you piston to square up the ring, then pull it out again..you are checking the ring by itself.

What I meant was since my pistons are still on the rods I can't use them to square up the ring.. I was wondering about the "bolt" method where you use a small bolt to push the ring down at various points around the cylinder to get it square.. using the bolt head to be sure it's at the same depth at each point.


thanks again,
-Corey

Offline flatlander

  • Old Timer
  • ******
  • Posts: 2,588
Re: Broken piston ring
« Reply #5 on: September 14, 2015, 12:23:31 PM »
So just simply replacing the rings isn't an option.. the cylinders need to be honed to help break in the rings?..

yes

After running the tool up and down the cylinder nothing fancy is required and I can then continue with gapping and filing the ring and reassemble the engine? 

yes, depending on what you call fancy  ;)

That is of course if the cylinders aren't egg shaped or tapered when measured with a bore gauge, in which case machining is required and there would be no point in just replacing the rings without doing so?

correct. when you have the cylinder off either measure them yourself or have them measured. this is a good time to find out if you need a rebore.

Sorry for the list of questions but does all this sound correct or am I missing something?  It seems this is rapidly turning from simple head gasket job to complete rebuild and, although I've never gone this far before, I'm not one to have someone else finish it for me.

it's probably more than you bargained for but look at the bright side: as you're going in now anyway, better make sure everything is checked and whatever needs to be done is done. then you'll be good for years to come.
in case it's not on your shopping list: you'll also need a new base gasket. and may want to replace o-rings (depending on your model).

What I meant was since my pistons are still on the rods I can't use them to square up the ring..

true but when you take them off the rods you can use them and that will probably be more accurate than using a bolt.
also, i've never done it that way but i imagine getting the rings on the pistons while they are mounted on the rods and quite close together, to be a bit fiddly creating more risk to brake one. maybe someone else can advise differently but i'd take them off.


Offline cj8990

  • Full Member
  • *
  • Posts: 56
Re: Broken piston ring
« Reply #6 on: September 14, 2015, 02:52:07 PM »
Thanks for the response!

I'll be checking the bore out this week then to see how it looks... lets say it has to be machined.. in that case I would need to have the cylinders bored out to a larger diameter but how would this effect my current pistons?  My understanding is that if the new machined bore minus my current piston diameter is greater than the clearance value set from the factory I'll need to get new larger pistons and rings to accommodate the new larger bore.  If it's less than the clearance value than I'm good reusing my same pistons?

Now does this sound right?  Last one I promise!

-Corey

Offline flatlander

  • Old Timer
  • ******
  • Posts: 2,588
Re: Broken piston ring
« Reply #7 on: September 14, 2015, 10:55:43 PM »
you'll be needing new pistons, next size up incl. rings, pins and clips. the stock honda oversizes are in 0.25mm increments.

Offline martin_uk

  • Hot Shot
  • ***
  • Posts: 272
  • CB750F1 CB750K8
Re: Broken piston ring
« Reply #8 on: September 15, 2015, 02:06:36 PM »
If you remove the pistons from rods to fit rings (it is easier), make sure you fit new circlips and use cloth at bottom to stop parts dropping in to crankcase as circlips have a habit of shooting out.

Sometimes you need to warm pistons with a hot air gun to get piston pin out after circlip removed.

Also make sure you space ring gaps and look for marks on rings near ends to designate top as can be different.



https://www.google.co.uk/search?q=spacing+piston+ring+gaps&tbm=isch&tbo=u&source=univ&sa=X&ved=0CCEQsARqFQoTCJumlf_2-ccCFU0v2wod7SIKzA&biw=1366&bih=657#q=spacing+piston+ring+gaps&tbm=isch&imgrc=CdCPbx3OsHsqCM%3A

When I was 16 I started a decoke on my 2 stroke BSA Bantam,decided to remove cylinder, broke a ring and dropped a circlip into crankcase. Thought it would be OK, but as soon as it fired, it shot up and jammed piston, so had to rebore  :-[

Learning can be expensive  ::)



« Last Edit: September 15, 2015, 02:17:06 PM by martin_uk »
CB750F1, CB750K8,  Triumph Street Triple R, AJS 350, Triumph 3TA