Trouble restarting when warm...
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SanJoseMichael
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- Posts: 17
- Joined: Mon Jul 23, 1973 10:24 am
Okay, when rings need replacing, I'm guessing the outside of the ring where it contacts the inside wall of the cylinder has decreased in diameter due to friction wear decreasing the ring's outside diameter. Is honing always necessary? (Okay, it may be a good idea but is it always necessary?).
If the ring itself has worn, shouldn't the inside wall of the cylinder be pretty much intact? I'd guess from a metallurgical standpoint, you'd let the ring take the brunt of the wear in a low-lubrication scenario in order to preserve the wall it comes into contact with, as the ring should be an expendable part of the design (like brake shoes and drums or rotors, shouldn't aways need to turn them...) I mean, make the ring softer than the wall of the cylinder and it's the weakest link in the design.
I'm really trying to talk myself out of this being a major repair...
If the ring itself has worn, shouldn't the inside wall of the cylinder be pretty much intact? I'd guess from a metallurgical standpoint, you'd let the ring take the brunt of the wear in a low-lubrication scenario in order to preserve the wall it comes into contact with, as the ring should be an expendable part of the design (like brake shoes and drums or rotors, shouldn't aways need to turn them...) I mean, make the ring softer than the wall of the cylinder and it's the weakest link in the design.
I'm really trying to talk myself out of this being a major repair...
Ring set is less than $20, head and base gasket are another $20. Not much cost involved.
As for the wear question, bad rings doesn't always mean hone....but since you have the jug off and you had a friction failure...this would be the time to do the jug as well. Most of the time the jug will measure within tollerence and you just have to buy a standard ring set, this is especially true if you do not have a catastrophic failure. (i.e. ring breaking and metal scraping the walls) and the engine was always oiled and not abused. If you look at the jug and see scratches and scoring from the rings burning up (can feel it) you will need a hone and oversized pistons and rings.
Always measure so that you do not waste the $40 spent for the above to have it fail withing 100s of miles.
As for the wear question, bad rings doesn't always mean hone....but since you have the jug off and you had a friction failure...this would be the time to do the jug as well. Most of the time the jug will measure within tollerence and you just have to buy a standard ring set, this is especially true if you do not have a catastrophic failure. (i.e. ring breaking and metal scraping the walls) and the engine was always oiled and not abused. If you look at the jug and see scratches and scoring from the rings burning up (can feel it) you will need a hone and oversized pistons and rings.
Always measure so that you do not waste the $40 spent for the above to have it fail withing 100s of miles.
Jeremy Ferch
1985 Spree (NQ50) - Mid restoration
1985 Spree (NQ50) - Mid restoration
I'll agree that you might not need a bore job, but anytime you replace rings you need to hone the cylinder. Honing the cylinder helps seat the rings. Jerry did this with emory cloth; I would recommed buying an inexpensive ($10?) brake hone from an autoparts place.
Measurement is critical, as mentioned above, and requires a bore gauge. This is what tells you what rings to buy, and whether you need a piston. Light scoring by the exhaust port is common, and may hone out. Deep scoring will require a bore job. If you can feel a scratch with your fingernail, it needs to be addressed.
Oil up the bore, use a drill to drive the hone up and down while spinning. You want to see a 60 degree cross-hatch (more circular than vertical,) this is considered optimal for ring seating. Don't overdo the honing; you just want to create the crosshatch, not increase the diameter. When you're done, lightly dress the exhaust and intake ports with 1000 grit sandpaper and water, to remove the sharp ridges from the ports. Sharp ridges eat rings. Clean the jug up with soap and water, dry (and hit with WD40 if you're not going to immediately reassemble it.)
Small-engine reboring is done the same way, but with larger, rougher stones and a heavier boring apparatus. You need a bore gauge to judge progress here, and make sure you aren't belling out the bore.
While you've got the jug out, it's a good time to clean the carbon from the exhaust port. Also a good time to polish the exhaust port. Don't enlarge it if you don't know what you're doing, but smoothing the passage can't hurt.
Have fun.
Measurement is critical, as mentioned above, and requires a bore gauge. This is what tells you what rings to buy, and whether you need a piston. Light scoring by the exhaust port is common, and may hone out. Deep scoring will require a bore job. If you can feel a scratch with your fingernail, it needs to be addressed.
Oil up the bore, use a drill to drive the hone up and down while spinning. You want to see a 60 degree cross-hatch (more circular than vertical,) this is considered optimal for ring seating. Don't overdo the honing; you just want to create the crosshatch, not increase the diameter. When you're done, lightly dress the exhaust and intake ports with 1000 grit sandpaper and water, to remove the sharp ridges from the ports. Sharp ridges eat rings. Clean the jug up with soap and water, dry (and hit with WD40 if you're not going to immediately reassemble it.)
Small-engine reboring is done the same way, but with larger, rougher stones and a heavier boring apparatus. You need a bore gauge to judge progress here, and make sure you aren't belling out the bore.
While you've got the jug out, it's a good time to clean the carbon from the exhaust port. Also a good time to polish the exhaust port. Don't enlarge it if you don't know what you're doing, but smoothing the passage can't hurt.
Have fun.
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SanJoseMichael
- Noob
- Posts: 17
- Joined: Mon Jul 23, 1973 10:24 am