cheers Dave
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| 20" + bore size in mm ?? https://www.ausmini.com/forums/viewtopic.php?f=2&t=48159 |
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| Author: | Brown Clubman [ Thu Dec 04, 2008 2:22 pm ] |
| Post subject: | 20" + bore size in mm ?? |
Can anyone tell me what size in mm at 1275 bored out 20+ should be ?? I've searched for "bore sizes" with no luck.. Thanks, Skender. |
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| Author: | sitnlo62 [ Thu Dec 04, 2008 2:45 pm ] |
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71.13mm Dave |
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| Author: | Brown Clubman [ Thu Dec 04, 2008 3:47 pm ] |
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cheers Dave
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| Author: | Brown Clubman [ Thu Dec 04, 2008 5:33 pm ] |
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ok .... so I brought my Dick Smith $30 digital calipers home and measured up the bores of the Clubman GT block I bought. When I bought the block I was told it was 20+. Measurements in mm from today are Front to back Cyl 1 71.08 Cyl 2 70.99 Cyl 3 70.55 Cyl 4 70.69 Left to right Cyl 1 70.92 Cyl 2 70.88 Cyl 3 70.90 Cyl 4 70.86 Manual says std bore sizes are: 70.60mm. Does that mean the block I bought is still standard bore with some "normal" wear?? Or should I buy a new digital calipers?? Cheers, Skender. |
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| Author: | Kennomini [ Thu Dec 04, 2008 6:03 pm ] |
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Have you got the pistons new yet? if not it may be worth getting it re bored to 20+ thou or 30+ or whatever the next size up is 
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| Author: | sitnlo62 [ Thu Dec 04, 2008 6:17 pm ] |
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The bore shouldn't show any, or very little wear above the top ring. With a vernier caliper you will only be able to measure the bore just below the deck.(above the top ring) My advice would be to clean any carbon from the bore in this area and remeasure. I think you will find it is already 0.020" oversize. Hope this makes sence.... Dave |
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| Author: | Brown Clubman [ Thu Dec 04, 2008 6:31 pm ] |
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yep, makes sense Dave. Cheers, Skender. |
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| Author: | drmini in aust [ Thu Dec 04, 2008 7:17 pm ] |
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Bore size is usually marked somewhere on piston crown. Std, +020, etc. I reckon it's standard, it may have been honed for new rings which will make the readings a bit bigger. +.020" oversize bore should show 71.1mm or larger, on all measurements |
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| Author: | Brown Clubman [ Thu Dec 04, 2008 7:32 pm ] |
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drmini in aust wrote: Bore size is usually marked somewhere on piston crown. Std, +020, etc. Doc - this block came without pistons so measurements would be the only way to tell. drmini in aust wrote: I reckon it's standard, it may have been honed for new rings which will make the readings a bit bigger.
+.020" oversize bore should show 71.1mm or larger, on all measurements Hmmmm, if correct that's pretty good news Doc. So you don't think cleaning it up will make much difference? 
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| Author: | drmini in aust [ Thu Dec 04, 2008 7:45 pm ] |
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I would just take the block to your machinist and have him measure then bore and hone it to the next oversize, or whatever bigger size you want. Don't even think about putting new pistons into old bores, it never works and is poor economy. |
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| Author: | Brown Clubman [ Thu Dec 04, 2008 7:54 pm ] |
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Quote: I would just take the block to your machinist and have him measure then bore and hone it to the next oversize...
that's the plan Doc. I'm just happy that i've got myself what appears to be a decent block, given I was buying it over the phone sight un seen it's a big relief. I know I stil have a fair way to go but sofar so good. Thanks for the tips. PS: my previous question about cleaning the bores up was referring to an earlier post that said cleaning them up might make a difference measurement wise.
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| Author: | simon k [ Thu Dec 04, 2008 8:09 pm ] |
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is good 
don't buy your pistons until the machinist has seen the block, then when he's happy with the size you're going to use, buy your pistons and take them to him to get the clearances spot on |
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| Author: | Brown Clubman [ Thu Dec 04, 2008 8:15 pm ] |
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simon k wrote: is good
don't buy your pistons until the machinist has seen the block, then when he's happy with the size you're going to use, buy your pistons and take them to him to get the clearances spot on you read my mind Simon.... that was my next question. And get the deck heights checked?? Is this essential? Some say yes some say no ..... |
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| Author: | drmini in aust [ Thu Dec 04, 2008 8:22 pm ] |
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I'd not deck it until you see what deck height is with the new pistons. Do this before you press fit the pistons on the rods. I use a home made dummy gudgeon pin which is a slide fit in the rod. If the pistons are too high it's then no big deal, you can get a bit faced off their crowns before they are fitted to the rods. I like to get mine around .010-.020" deck height...
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| Author: | TheMiniMan [ Thu Dec 04, 2008 8:27 pm ] |
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Use a bit of old broom stick or wodden dowel machined down as a "Dummy" gudgeon pin, slide fit as the good Doc says works a treat
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