Rebore

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Headcoats
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Rebore

#1 Post by Headcoats » Sat Aug 05, 2017 4:51 am

I had some barrels bought second hand several years a go and they came with 1.00 rebore and fresh pistons, never ran
Fitted them and they rattled but not terminal, so rode it like this for a few years then I changed barrels

Now I'm building the second bike and took these barrels in to the local engineers and he reckoned 1.25mm over might not be enough to clean them up and said 1.50mm might be what they end up but said he would ring me first

Is this normal then to jump 2 sizes , there was scoring but nothing looked deep
That original 1.00 re bore though was never right even though it went like stink and made 68bhp on those barrels with a Mick Abbey tune

Also if I end up with 1.50mm bores, will the head gasket still be OK , as in no trimming of the inside diameter ?
Cryin' In The Beer Of A Drunk Man

yazza54
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Re: Rebore

#2 Post by yazza54 » Sat Aug 05, 2017 6:08 am

It's more about getting the bore round than taking out scoring. He's probably come to that conclusion because the bores are slightly oval, so you'll just have to jump 2 sizes if that's what it takes to get I back in shape. If it was loose in the first place that will have accelerated the process in wearing the bores oval.

Headcoats
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Re: Rebore

#3 Post by Headcoats » Sat Aug 05, 2017 6:36 am

I had better accept the 1.50mm re bore then !
Won't have much life left in them then ?

There is always the question to what is the maximum you can bore YPVS 350 barrels out to
Is 2.00mm the limit really ?

I have some more barrels on 0.5mm but haven't got the Mick Abbey tune on them
Cryin' In The Beer Of A Drunk Man

yazza54
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Re: Rebore

#4 Post by yazza54 » Sat Aug 05, 2017 7:09 am

Can't you just have a new steel liner pressed in when they get to the end of their life? Get the ports re dressed to match the ally and you're good to go again

Headcoats
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Re: Rebore

#5 Post by Headcoats » Sat Aug 05, 2017 7:27 am

Think you can but it is quite expensive
Cryin' In The Beer Of A Drunk Man

yazza54
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Re: Rebore

#6 Post by yazza54 » Sat Aug 05, 2017 8:04 am

Well you'll get more life out of the bore if you change the pistons more regularly and that's certainly cheaper than re sleeving it

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T.RexRacing
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Re: Rebore

#7 Post by T.RexRacing » Sat Aug 05, 2017 8:27 am

Yeah I do pistons every 10K miles or so. Bore usually lasts 3 pistons before needing work.
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bitzz
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Re: Rebore

#8 Post by bitzz » Sat Aug 05, 2017 11:12 am

yazza54 wrote:Can't you just have a new steel liner pressed in when they get to the end of their life? Get the ports re dressed to match the ally and you're good to go again
...except the liner is cast in the jug. Most are pressed in.
Replacing the liner is doable but it probably easier to find replacement jugs.

Headcoats
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Re: Rebore

#9 Post by Headcoats » Sat Aug 05, 2017 1:58 pm

Yeah I can't say I'm keen on re sleeves
I do have some more barrels but don't have the famous Mick Abbey tune (UK)
Cryin' In The Beer Of A Drunk Man

waltmil
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Re: Rebore

#10 Post by waltmil » Sat Aug 05, 2017 6:29 pm

Do you have any one who can plate your cylinders? There are a couple here in the US that do it. It is expensive but maybe worth it if you like your porting.
Red/White US '84, Spec II pipes, Y-boot w/K&N, Fox Shock, Mikuni carbs?

Headcoats
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Re: Rebore

#11 Post by Headcoats » Wed Aug 09, 2017 6:27 am

Engineering place just rang and they put the 1.50mm bore through and it still hasn't cleaned up the inlet sides and he now is going 1.75mm which is a shocker really as I didn't expect that and that might not do it !
I have some more barrels on 0.5mm but haven't got the tune , so a big dilemma what to do
Cryin' In The Beer Of A Drunk Man

evan_calgary
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Re: Rebore

#12 Post by evan_calgary » Wed Aug 09, 2017 11:44 am

Must say that is quite surprising. I had a pair of barrels that had been bored crooked and only took .5mm to correct.

Headcoats
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Re: Rebore

#13 Post by Headcoats » Wed Aug 09, 2017 2:02 pm

They are a well used firm here in the UK and are a handful of trusted places to use but I don't like this at all !
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MK
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Re: Rebore

#14 Post by MK » Thu Aug 10, 2017 8:57 am

My current set of cylinders is +3.25 mm but the liner is thin as paper in some locations.
I'd consider them as 'to be resleeved' after the next damage.

Going bigger than expected is normal as usually the bore is not perpendicular to both sealing surfaces. So you always need some 10'th to compensate that.
Second issue is that re-bore was done out of center. That may rob you a few overbore sizes at the end of the life.
Bye
Martin

Headcoats
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Re: Rebore

#15 Post by Headcoats » Thu Aug 10, 2017 11:18 am

3.25, is that a typo ? Did you mean 2.25mm
Wow I only thought 2.00 was the max or 2.25 for the brave !
Cryin' In The Beer Of A Drunk Man

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