Flex-Hone method for cylinder honing

Competition engines and 'live' projects only. Good photos to illustrate your post are expected.
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Georges Fonso
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Flex-Hone method for cylinder honing

Post by Georges Fonso » September 14th, 2007, 12:33 pm

Dear GC and all,

I see you (GC) put great faith in Flex-hone, and I'm sure you've got your reasons for that, but I'm a bit reluctant to try honing by hand on a really high spec engine -- that is I don't trust my hands that much. Deglazing for a budget reconditioning of the "rings, seals and bearings" type is probably another story, and FlexHone is something i'd like to try for this kind of jobs... But I'm wondering if and how easy it is to get it wrong and end up in the machine shop for a rebore...

To date I always specify plateau honing in rebored engines. There is a machine shop in Athens that does it (to my knowledge they're the only ones in Greece, unfortunately), they know their stuff and do it the way it should be done. They have a a Sunnen honing machine and use Sunnen's proprietary diamond honing stones and steel plateau honing "brushes". We always achieve excellent results with rebored and Sunnen-honed cylinders, always matching the crosshatch and roughness to the provisioned use of the engine and, of course, our pistons and rings.

I sometimes machine-hone in order to deglaze as well, but only after checking that the available new rings options won't wreak havoc with endgaps after honing... Otherwise i call it a rebore.

Do you think an otherwise adequately skilled engine builder can play "novice Flexhoner" so as to easily save himself time and effort -- but without grief?

Thanks!

GF

Guy Croft
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Post by Guy Croft » September 14th, 2007, 1:02 pm

OK - nothing wrong with what you are doing.

But the Flex-Hone final honing method is proven beyond all dispute by everyone who has used to be better.

You yourself might typically use it after the bore has been bored to within say 2 thou of finished size, honed by parallel stones to dead size. The Flex-Hone is then used to generate a plateau-honed finish almost devoid of folds and tears and with the graphite in the cast iron fully exposed for good oil retention.

The trouble with diamond hones - and yes I know lots of people use them and get adequate results - is that because they are designed to hone to very fine tolerances they are extremelly hard and cause a lot of folded metal (microscopically) on the bore surface. So what? Well, it covers up the graphite.

Interestingly, Van Norman and Kwik-Way - who are famous manufacturers of boring bars have approved Flex-Hone for immediate post-bore final honing with no intermediate parallel honing op. Of course to do this successfully you have to be able to bore with a high degree of accuracy (0.0005") - more or less to finished size with a low CLA surface texture, which few shops can really do adequately.

You should really read Brush Research Manufacturing's website. The story of their battle to be recognised is really fascinating. They produce fantastic books on - guess what? Honing! Which no-one else does! They get stiff opposition among reconditioners from the sellers of honing equipment. I know of guys who have spent months with really expensive honing machines trying to generate what I can do with a drill and Flex-Hone in 2 minutes flat! They laugh when I tell them how I finish hone. True!

I first used a Flex-Hone in 1988, and the speed with which my engines bedded-in, and how well the bores and rings lasted on GC units (hundreds) as a consequence, was proof enough for me. It could be for you too..

GC

Georges Fonso
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Post by Georges Fonso » September 14th, 2007, 1:51 pm

Goodevening, GC!

Aren't the steel plateau brushes meant to "shave" what the diamond stones leave behind, and "unfold" the graphite? What if one was to use normal grit stones instead of diamond, and then brush the walls in order to produce plateau finish?

I'll read the BRM site thoroughly and come back with any new thougths on the subject.

A couple of them stem up already, such as cylinder wall parallelism throughout the bore height as well as bore taper (wether we intend to have one or not, in the first place...).

GF

Guy Croft
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Post by Guy Croft » September 14th, 2007, 2:45 pm

See photos:
Attachments
GC 088.jpg
Old used bore, some scratching from detonation but otherwise straight and true within same limits I built it..
GC 088.jpg (106 KiB) Viewed 9805 times
GC 089.jpg
30 sec honing with self-centring Flex-Hone 240 grade silicon carbide dresses flawlessly for moly-inlay top rings. Fool-proof..
GC 089.jpg (107.58 KiB) Viewed 9147 times
GC 090.jpg
prior to hot wash in water with detergent (and corrosion inhibitor) I use a (new!) toilet brush in my drill with strong detergent solution to get right down to the oily gritty mess the hone leaves behind. Vital!
GC 090.jpg (111.93 KiB) Viewed 9146 times
GC 087.jpg
And now a word from my sponsor.. Castrol GTX is the perfect bore honing oil. Flex-Hone in use. How can anything so seemingly basic be so good? Doesn't happen often in race engine pre..
GC 087.jpg (111.8 KiB) Viewed 9145 times

Evodelta

Post by Evodelta » September 14th, 2007, 5:38 pm

Guy,

Which size do you use for a F/L 2 litre bore of 84.4 - 85? A GBD 3.5" (89mm)?

Thanks,
Martin.

Guy Croft
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Post by Guy Croft » September 15th, 2007, 6:50 am

Yes, that is the one & just in case you were not sure you don't need the heavy duty one.

If you buy please contact Pacehigh Ltd - UK sole appointed agents - old friends of mine, nothing in it for me - do mention my site please. They frequently help me with important tech info that is published here. They are quick and super reliable.

GC

Brit01
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Re: Flex-Hone method for cylinder honing

Post by Brit01 » July 4th, 2011, 6:53 pm

Hi,

Just brought up your old thread because I'm rebuilding my flat 4 boxer.
New cams/tappets/oil pump.
It only has 18,000 kms since the last honing.

But I have replaced the piston rings and concerned about de-glazing the bores before replacing the pistons.

If I post a photo of their current condition could you give some advise on whether I need to do a home diy de-glaze as you have done easily?

I heard this:
As long as you see hone marks, don't do any thing to the bore. Just install new piston and rings
I will give them a good scrub with a scotch pad and wd40 and take a photo.

Thanks

Brit01
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Re: Flex-Hone method for cylinder honing

Post by Brit01 » July 5th, 2011, 11:48 pm

photos of current state of cylinders:
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cross hatch 3.JPG
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cross hatch 4.JPG
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cross hatch 5.JPG
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cross hatch 6.JPG
cross hatch 6.JPG (63.34 KiB) Viewed 8078 times
cross hatch 7.JPG
cross hatch 7.JPG (54.92 KiB) Viewed 8078 times

Brit01
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Re: Flex-Hone method for cylinder honing

Post by Brit01 » July 6th, 2011, 4:02 pm

GB 3 1/2" 240g A/O -This hone is suitable for Nikasil Coated Blocks/Barrels if cast iron /Steel 120g S/C would be more suited and cost effective
Pacehigh Limited stated the above.

So for my standard flat 4 boxer I'll need the 120 grit?? Bit rough in my opinion


I found this ;

3 1/2 Flex-Hone tool silicon carbide 240 grit (89mm)
for 32 USD!
Product Description (Item# 312240sc)
Working range 3.050"-3.550" (75mm-90mm). Hone is 14" long. Great for steel cylinders
Bit contradicting between the 2 suppliers in regards to the grit.

I'm inclined to go for the 240 grit. less is better, can always spin it for longer.

Update: Flexi Hone ordered in USA (no time left as colleague is flying out next week).
89mm S/C 240 grit Flexihone GB.


Thanks

WhizzMan
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Re: Flex-Hone method for cylinder honing

Post by WhizzMan » July 6th, 2011, 11:03 pm

The 240 should be fine.
Book #348

Brit01
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Re: Flex-Hone method for cylinder honing

Post by Brit01 » July 7th, 2011, 12:10 am

great.

too rough and I guess it can cause excessive wear on the rings.

regards

Guy Croft
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Re: Flex-Hone method for cylinder honing

Post by Guy Croft » July 7th, 2011, 9:42 am

240 is too fine in my opinion for chromed top rings they may never bed in. 180 is right for them.

I have cross-checked this with BRM and CP directly in conversation (many years ago) and have had this regime in place since I ever heard first about Flexhone in 1990.

Anyone who wants to do otherwise be my guest.


GC

Brit01
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Re: Flex-Hone method for cylinder honing

Post by Brit01 » July 7th, 2011, 1:29 pm

May be able to get the 180 grit to arrive in time. The seller ships them out very quickly as a priority for workshops.

Thanks for your advice again.

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