Hepolite pistons in a CB72

[AshimotoK0]

Bad news is that my CB72 engine....I thought had STD bores I find has been bored out to +1.00 mm  and I was going to rebore with new pistons due to surface rust due to standing. I do have a second set of barrels at the stash but  rusty bores and not sure if previous re-bored. I noticed you can get Hepolite  old stock +1.50 but are they any good, anyone know?

[Trigger]

Nowt wrong with Hepolite, used shed loads of them in the late 80's 

[taysidedragon]

Nowt wrong with Hepolite, used shed loads of them in the late 80's 

I second that. 

[mickwinf]

good quality stuff, sold loads of them when i was in the motor trade.

[Orcade-Ian]

How bad is the rust Ash?
My CB77 had very rusty bores after someone stripped and left the top end in bits for years.  They cleaned up a treat with my glaze buster and it runs like a good ‘un with no smoke.  The very tiny pockets where the rust was, act as oil reservoirs, no bad thing.  In fact there used to be barrels available for C15 Beezers with dimples in - Trig might remember them and as he said Hepolite are very good (Yorkshire folk tha’ knows) Hepworth and Grandage,
Ian

[AshimotoK0]

Will grab my spare barrels from the stash tomorrow and measure them.

[Tomb]

Yup, nowt wrong with Hepolites, got them in my Trumpet.

Strangely I have CB750 +0.5mm pistons in my CB72....    and liners

[Bryanj]

Hepolite made all the UK pistons at one time and are good quality, it used to be a common thing to have barrels bored the leave them in the garden for a couple of weeks to get the afore mentioned "dimples" to hold oil when racing

[AshimotoK0]

Went to my stash and the rusty bore spare ones are standard size...phew ! I  just need to clean up and assess how deep the rusting is.
A guru  on the 305.com site told me that Hepolite CB72 pistons are too high compression for a standard bike and that their gudgeon pins wear badly if used with Honda little ends. Luckily too, no fin damage on them.

[Orcade-Ian]

Hi Ash,
The rusting would have to be REALLY deep to give me any cause for concern.  Good grade meehanite which I believe was used by Honda certainly does rust but nearly always cleans off to useable metal underneath.  If your spare standard barrels have been left bare (without pistons popped back in) then that would be a bonus.  If the pistons are in that’s when the trouble can start around the rings.

Ian

[AshimotoK0]

Hi Ash,
The rusting would have to be REALLY deep to give me any cause for concern.  Good grade meehanite which I believe was used by Honda certainly does rust but nearly always cleans off to useable metal underneath.  If your spare standard barrels have been left bare (without pistons popped back in) then that would be a bonus.  If the pistons are in that’s when the trouble can start around the rings.

Ian

No Ian no pistos just bare bores left for ages to rust.. what grade of paper/Scotchbrite should I use to clean up? I do have a red Scotchbrite drill operated multi disc ..would that be any use with something like WD40?

[Tomb]

If the bores are good apart from the rust a 320 wet+dry paper will work well, diagonal movements to mimic the honing original marks. DON'T polish the bore. WD40, paraffin, or dry is ok.

Luckily too, no fin damage on them.

The early CB72/77 barrels had none pressed fit liners, they would slide out by hand so swapping liners out is easy if you wanted to put them in different barrel/fins.

[Orcade-Ian]

As tomb says,
320 will be OK if you can remove all the rust with it and definitely try to mimic the cross hatching.  You can go rougher than 320 and come back.  You will not really be able to remove any significant amount of metal - even a thou will take hours to remove by hand.  I sometimes make up a simple slotted spindle - piece of half inch round bar with a slot cut in and wrap emery tape around and then whizz it around in the drill till all the rust is gone.  Dry to start with, then lubed with WD.

Ian

[AshimotoK0]

Well I cleaned up and remarkably the rusty bores  came up fairly nice as you described Ian with very little effort. One bore has a minuscule ridge at the top though. I inserted a NOS STD piston upside down with the skirt positioned just below the ridge and I can just tightly trap a 2 thou' feeler between the bore and the piston (front thrust side). However, I can do exactly the same on the other side that has no discernible. What do you reckon everyone?

[Orcade-Ian]

Do you have acces to a glaze buster - the 3 spring loaded stones type? That tiny ridge might come out with one.  There is always the slight risk that a new top ring can be broken by a ridge if it’s big enough.  Don’t know if stepped top rings are available these days.
Is Waterloo Engineering still trading - they might be able to help.
Ian