View Full Version : Rebore or not to Rebore ?
Right, been speaking to a very knowledgeable friend of mine and this is what he has said.
When the block is inspected by the engine builders, if it's not worn, or not in need of a rebore, then leave it alone, and only get it rebored if it Really needs it ? (it's a C16SE btw)
So, will the extra 30-40cc capacity not really make a difference on BHP ? or should i go with what he says and spend the ?270 on something else .. Prehaps get the Conrods shotpened and de-seamed ?
Thanks Nick
Snowface
15-02-05, 06:28 PM
i got mine done for ?200.
there will be a difference in power/torque, but not a great deal.
(engine capacity is directly linked to torque.)
david dixon
15-02-05, 06:32 PM
get the head slightly flowed or buy some nos! you'll see more power with a 25 jet than you will boring it out.
but is it worth doing if it really doesn't need it ?
will other items of work that cost simlilar produce a better gain ? if so, an example would be nice :-)
Snowface
15-02-05, 06:40 PM
stage 1 blydenstein cylinder head work will give quite a bit more than a rebore and costs ?250 +vat.
yep all the usual stuff is getting done,worked big valve head (not a bly one tho) Cam, ARP bolts, Soild lifters, crank flywheel e.t.c
if he turns around and says it's not neccessary, is there anythng apart from the usual that i can get done for a similar price that would give a better gain ?
mikey14sr
15-02-05, 07:03 PM
If the bores aren't worn then just a slight honing and a set of new standard rings should bring it back to life. This is what I've just done to my little commuter bike and it flys in comparison to before I did it.
If you've got a copy of the group A build manual, that has a few good ideas in it, like baffling the sump, upping the oil pressure and fitting an oil cooler, all of which will help keep your engine alive a bit longer.
NickWalliams
16-02-05, 02:40 PM
If your gettin everything else done, then get the bores done for definate. Id do what mikeygte says if the bores aint too bad. 8)
if your building to the spec you say then id have thought that de seamed and shot peened rods would have been near top of the list lol
Snowface
16-02-05, 05:53 PM
what effect does de-seaming and shot peening have on the rods? how is it meant to improve them?
Camb, i've enquired about conrods and they say the standard GM rods will be adequate to withstand 150bhp. They jst recommend balancing them
so the top and bottom half of them are balanced as a set first.
Snowface, shot peening is just blasting the conrods with ball bearings to reduce the possibility of stress cracks and generally make the Conrod more compact.
I'm not sure about de-seaming, but as far as i'm aware it provides similar advantages in terms of stress durability and strength.
if your running silly BHP steel conrods, Alu Billet, or even titanium billet conrods would be used. - but that's drag car stuff really. (except for steel)
the power isnt so mush an issue, the RPM is.
deseaming and shot peening prestresses the surface and therefore reduces the ammount of located stress. so its made stronger without doing silly things to them.
its basically a good idea for a reliable bottom end thats not gonna throw a rod.
yes GM rods are good for 150 + but you can make them more duralbe with the above processes
its a good idea to rebore really, the rebore isn't that much money really and if you are going to build a nice reliable engine then do properly, with a re bore and new pistons your basically starting with fresh internals which always helps although older looser engines will rev easier but this dows not mean they will last.
Lightening and balancing them seems to help a bit and its another thing that is a good idea when rebuilding to a higher spec.
with a .5mm overbore, Blydenstein head and a good cam kit you can easily see over 140bhp using weber 40's, without going to the extreme either
Rob-16v
16-02-05, 10:17 PM
So how much does it cost to get the block re-bored and new pistons?
it's about ?25 a bore, and ?100 for a set of pistons
so you need a set of pistons and 4 bores.
+ labour
so ?200 is a v.good price, snowface got it done for that.
?250 is a good price
Anything ?300 and over is overcharging IMO
it depends how much work needs to be done really as well.
Rob-16v
16-02-05, 11:05 PM
So where do you bigger pistons from? you can buy a fully re-con engine for ?420
take it to an engine builders/engineering company that is able to rebore blocks.
say to them " hello mate, i would like a rebore and oversize pistons e.t.c"
he will no doubt advise you on the extent of the overbore, and he'l make/order new pistons to match, or go with some figures in mind.
e.g a local place to me is lancaster engines, if i take the whole block down they will rebore it, oversize pistons, balance the conrods and shotpeen and de-seam them, arp bolts, lighten and balance the flywheel and crank.
pretty much most of the bottom end work, they'l do the same at most places as it's all machining work.
Aragorn
17-02-05, 10:17 AM
apparently shotpeening helps because its surface cracks that cause the majority of failures
a bloke on mig (chip iirc) done some experiments with breaking strain of std XE rods and even scoring one across the stem with a hacksaw blade significantly reduced the strength of the rod
shotpeening works by prestressing the outer surface to remove any microscopic cracks (they will actually move inside the rod but thats not important) which makes them stronger[/b]
Rob-16v
17-02-05, 05:38 PM
Iv just called a place in york and the rebore for ?50, thats for all 4 cylinders. Just priced up re-bore, pistons+rings,regrind the crank and new shell, it came to ?280ish. Is that cheap??
yep 280 seems a good price for all of the above mentioned.
you probably wont find anything considerably cheaper.
Aaragorn, they shotpeen using a ball bearing gun (or something similar) don't they ?
Rob-16v
17-02-05, 06:06 PM
Nick are you trying to get 140bhp out of a 1.6 then?
155 is my new goal, maybe unrealistic tho...
however, i will be very pleased if it goes near to 140bhp.
at least make sure you get the bores hone'd and some std size rings, imo you wouldnt ntoice the difference with a .5 over bore etc as said spend the money on a nos set up, as you have a strong bottom end which should take the abuse!
yep i will do, all depends on what condition the engine is in really.
the engine i have available to me at the moment has done alot of miles, and i know it's been abused a fair amount.
i think i may start looking around again for a better condition engine, and hopefully not have to go for a rebore, just concentrate the money on other things.
i'l see what he says
yep 280 seems a good price for all of the above mentioned.
you probably wont find anything considerably cheaper.
Aaragorn, they shotpeen using a ball bearing gun (or something similar) don't they ? shotpeening uses little glass beads
ace, your not as stupid as you look :-) lol :lol:
cheeky coont
if they try and charge you more than ?50 to do the shot-peening tell the to fook off and do it yourself with one of these http://www.demon-tweeks.co.uk/catalogue/product_detail.asp?PCODE=SEASB993&GRP=MP079&PGRP=M005&CLS=MSPORT&from=search
http://www.demon-tweeks.co.uk/resources/images/detail/SEASB993.jpg
and some of these http://www.demon-tweeks.co.uk/catalogue/product_detail.asp?PCODE=SEAB5KG&GRP=MP079&PGRP=M005&CLS=MSPORT&from=search
somhow i don't fancy being blasted in the face by rebounding bits of glass
lol, pretty cool tho...
use a mask or get one of these
http://www.demon-tweeks.co.uk/resources/images/detail/SEASB972.jpg
or even ,ale one it wouldnt be that hard
What... like this guy ? nicely sporting his shotpeening Suit???
http://www.geocities.com/phatrobotsuit/HipRobotSuit.jpg
if the engine has fook loads of miles on id go for the .5 over bore, you can retain the standard pistons on the .5 aswell.
Rob-16v
18-02-05, 10:48 AM
Nick, are you going to be using new oil and water pumps, and a new cam?
yep i've got a Kent AST2 complete kit (valve springs e.t.c) on my account at the mo, jst have to pop in and pay for it.
As for water and oil pump, the enigne is having a complete rebuild from scratch, the only parts i intend to keep on the engine are the alternator, starter e.t.c
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