Race Engine Forum UK

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

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

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

See photos:

Guy,

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

Thanks,
Martin.

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

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

photos of current state of cylinders:

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

The 240 should be fine.

great.

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

regards

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

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.