My Haynes manual recommends "honing" the cylinder bores before fitting new piston rings. What does this achieve?
By eye, the bores look perfect, there is no ridge at the top,
no scores or other visible damge. The pistons do feel tight in the bore I must say but I put this down to the new rings.
Honing = dismantling again, so, is it worth it?
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yes you must hone or the rings wont bed in but sit on the glaze of the wall.........sorry
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yes you must hone or the rings wont bed in but sit on the glaze of the wall.........sorry
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You must have clicked on the return button a second faster than me !
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Yes it probably is worth dismantling. Honing allows fast bed-in of new rings to an old bore which is probably fairly glazed. If you dont hone, ie rough-up the bore surface, you suffer extended ring bed-in and possibly slightly inferior compression/higher oil consumption for the rest of the engines life. The bore may look perfect to you but it probably doesnt look perfect to your new rings.
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Honeing is a form of grinding. If you have it done be aware that some machine shops will not take responsibility for cleaning the swarf away. In effect this is a grinding paste. Take time to ensure that the bores, oilways, bearing seating faces, coolant passages etc are ALL perfectly clean before any new parts go anywhere near the block.
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Also, if the honing is incorrectly done, it will increase oil consumption, I forget reason why?
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Steve
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Just hone it mate,you can hire them for a £5 or i think machine mart do one for nearly nowt
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very easy to answer:
get the bores honed. BEFORE you run it - if you've already run it, you've already ruined it.
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Even Halfords sell them.
Why go to the extent of changing rings and rebuilding the engine and then reading the manual?
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Also I'd strongly recommend using proper 'running in' oil after renewing the rings- and honing the bores. Modern oils are just too good in this situation and don't necessarily allow the rings to bed in. This is based on personal experience with my MGB GT V8. I changed the pistons & rings but didn't hone & refilled with my usual oil. Result- consumed 1 litre of oil per 1000 miles and blew out oil & pinked under acceleration. So I stripped it down again, honed it myself using a cheap car accessory shop honing tool, and ran it with running in oil for 500 miles or so. Result- 50,000 miles later it still doesn't use a drop of oil between services.
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Although I'm a mechanic I haven't rebuilt an engine for many years, it just isn't cost effective these days.
Honing, or glaze busting as it used to be known, is an essential operation when renewing pistons and rings.
The basic glaze buster is just a bore sized flap wheel. Back in the 70's and 80's Leyland A and B series engines used to suffer from glazed bores due to light service running, resulting in oil burning and loss of compression especially when hot. The quick and cheap answer was to remove the head and glaze bust as much of the bore as was possible - it used to work as well.
Again, going back a few years, diesel engine manufacturers used to recommend a period of hard loaded running prior to shutdown to prevent the glazing caused by light loading hot running. A bit at odds with the current recommendation of allowing turbo engines to idle for a few minutes after a hard run.
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Exactly. I had been going to suggest merely winding each piston to the bottom of its bore and then giving a whirr with a flap wheel in the old black & decker. But someone would have asked about the dust.
How valuable is this car? Is it a treasured classic where taking the pistons out again in order to do a perfect job is of no consequence, or just an oil-burning old banger that you want to get back on the road at minimal cost and effort?
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OK the pistons are in the the big end are on. The bores have not been rebored so the bores will not be round any more but slightly oval in the direction of the crankshaft throw. This is not ideal for new rings at all and the use of a honing tool would have been of great advantage to even things up a bit without going plus sized pistons and rings. This excludes a honing tool as it may leave unhoned areas but I would give it a try. Use grease to fill the gap when the pistons ( 2) are at bottom dead centre then hone the bore moving the tool from top to bottom at a rugular rate to produce a diagonal overlapping pattern at about 15 degrees and the surfave is matt. If the pattern is contiguous then all is well. Now move the piston up 1cm and back down and coolect the debris. back down, back up and clean again. Clean well and repeat for the other two pistons.If you do not have a honing tool to try just use 1000 grit wet and dry paper and matt the bores in a similiar pattern clean thoughly and complete your build. The bit that does not get honned at the bottom of the stroke. is under no real pressure as these is no compression at that point and the piston is moving relatively slowly. If it where me I would not be putting new rings and pistons into a used a bore unless measurement and honing put it within spec for diameter and ovality. Having said that I have seen several engines at 70K plus with very near perfect bore dimensions particulary VW Polos and Volvo's. The choice is yours but do not run new rings on glazed bores or you will melt the ends of the compression and oil control rings. Regards Peter
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