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Post by jon on Aug 13, 2020 17:09:28 GMT 1
Hi all,
I got a daft question about cc. We all refer to the larger capacity LCs as 350s. Even if at standard bore they are 347cc, and 2.5 overbore 375cc.
So why is a 66mm bore piston such a a DT conversion called a 375cc, when itโs actually more like 369cc. So rounded up.
Also a +4 crank motor is referred to as a 385cc. But with a standard bore it only 373cc. So rounded up again.
Iโm only asking as I want decals for my +4 crank YPVS on 65mm bore (so around the so called 385cc). Iโm not changing the decals and logbook every time I get a rebore LOL.
Is the general consensus a +4 crank bike is called a 385 regardless of bore size?
Jon
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Post by Yogi on Aug 13, 2020 17:20:17 GMT 1
Well mine is at 65mm with a +4 crank so is a 385 ๐
Just donโt put the cc on the bike,,problem solved,,mines not got any
Our bikes start off at 347 but are called 350s,so just rounding up
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Post by st66 on Aug 13, 2020 18:01:13 GMT 1
Why??! Why would you change the decals or the log book even, for bragging rights???, personally I'd leave it at 350 and I am,, your insurance will love you when you tell then its a 396 or wot ever it is,,,
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Post by reedpete on Aug 13, 2020 18:01:25 GMT 1
Hi all, I got a daft question about cc. We all refer to the larger capacity LCs as 350s. Even if at standard bore they are 347cc, and 2.5 overbore 375cc. So why is a 66mm bore piston such a a DT conversion called a 375cc, when itโs actually more like 369cc. So rounded up. Also a +4 crank motor is referred to as a 385cc. But with a standard bore it only 373cc. So rounded up again. Iโm only asking as I want decals for my +4 crank YPVS on 65mm bore (so around the so called 385cc). Iโm not changing the decals and logbook every time I get a rebore LOL. Is the general consensus a +4 crank bike is called a 385 regardless of bore size? Jon Just custom and practice.....bit like when you answer to someone who asked โHow old are youโ ? itโs only children who thing 1/4s are important ๐
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Post by oldbritguy on Aug 13, 2020 18:03:10 GMT 1
My old Norton Commando is an 850. It is actually 828cc so itโs ok to round up ๐
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Post by veg on Aug 13, 2020 18:06:19 GMT 1
Is this what Matt means when he says 12 inches?
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Post by Yogi on Aug 13, 2020 18:09:02 GMT 1
Is this what Matt means when he says 12 inches? No veg thatโs me rounding down ๐,,no one likes a big head thatโs why I donโt say 12 and 1/2 ๐ช
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Post by veg on Aug 13, 2020 18:10:36 GMT 1
Pmsl ๐ Sorry Jon.
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Post by Tobyjugs on Aug 13, 2020 18:11:34 GMT 1
I'm going to rename my track bike project the Bakker 125.
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Post by jon on Aug 13, 2020 18:11:55 GMT 1
Why??! Why would you change the decals or the log book even, for bragging rights???, personally I'd leave it at 350 and I am,, your insurance will love you when you tell then its a 396 or wot ever it is,,, Itโs not a case of bragging rights, but OCD. I wouldnโt feel right having a decal saying 350. Insurance is no problem if mods are declared to the right insurer. After all how many hybrids do you see running around with big bore motors. Do you honestly think they have all kept quiet about mods, and risk invalidated insurance on ยฃ10k+ bikes? Maybe just go for RDR similar to the RZR decals, as thatโs the paint scheme Iโm considering for my Brazilian model. Jon
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Post by stusco on Aug 13, 2020 18:12:17 GMT 1
On my gamma my logbook says 400 but i told the insurance it was bored to 460 it made no difference to the price
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Post by Yogi on Aug 13, 2020 18:13:53 GMT 1
I do actually declare my bike as a 385 insurance wise and all the other mods too
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Post by veg on Aug 13, 2020 18:14:44 GMT 1
If mine had a tz750 barrel Iโd have had the correct cc, as it was I nearly did have RZ 350 not RD as itโs a mix of Rd and Tz. And youโre right Jon you have to declare it all otherwise you invalidate your insurance. Could be wrong but think st66 was having a joke ๐ค
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Post by st66 on Aug 13, 2020 18:18:56 GMT 1
No Jon mate I wasn't being funny so to speak mate re bragging rights comment I just couldn't see why you would change it mate re the decals,, but you can do as you wish mate and I whole heartedly say if you want to yeah just go ahead, it's just an opinion mate I mean you put rz or Rd 385 on it and it will get looks yeah most deff, good or bad I couldn't say but it will have folk talking for deff,,, example you put 350 on her and its fairy fast,,,, sleeper type thing,, or do you advertise it 385 or more and it oh he's done the motor,,, or comments I won't say here,, can you see where I'm coming from mate,, but then again it may not even get a thought mate so it's your bike mate do wot you feel is right mate ๐๐๐
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Post by midlifecrisisrd on Aug 13, 2020 18:19:24 GMT 1
Mine is also +4 and 65mm bore so again it's 385cc
Logbook not changed but declared on insurance
Mine does say 385 on the side panels ๐
May be wrong but I thought the 375 lc was a last chance saloon job after you had used the last overbore of +2mm on LC pistons
The 375 used +0.5 DT pistons which gave 66.5mm bore
Were 2.5 over of pistons not a recent (not the 80's) thing
Now the resleeved 66mm 250 barrels are 370
Steve
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Post by st66 on Aug 13, 2020 18:20:55 GMT 1
Veg gets a curry whurrly,,, ๐either way Jon mate yes most deff declare it to insurance I wasn't suggesting otherwise that's just silly to put effort time and money into it just to void it incase the unspeakable happens no deff declare the mods ๐ANTH,
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Post by jon on Aug 13, 2020 18:24:15 GMT 1
Mine is also +4 and 65mm bore so again it's 385cc Logbook not changed but declared on insurance Mine does say 385 on the side panels ๐ May be wrong but I thought the 375 lc was a last chance saloon job after you had used the last overbore of +2mm on LC pistons The 375 used +0.5 DT pistons which gave 66.5mm bore Were 2.5 over of pistons not a recent (not the 80's) thing Now the resleeved 66mm 250 barrels are 370 Steve I guess thatโs whatI was trying to say. To do a DT piston conversion initially gives you around 370cc. Your right the last chance Saloon is 66,5mm whether a +0.5mm DT piston or +2.5mm LC piston. BUT do you refer to the bike as it was first changed? As I said originally a daft question really, but an interesting one? Jon
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Post by veg on Aug 13, 2020 18:25:24 GMT 1
Veg gets a curry whurrly,,, ๐either way Jon mate yes most deff declare it to insurance I wasn't suggesting otherwise that's just silly to put effort time and money into it just to void it incase the unspeakable happens no deff declare the mods ๐ Curry whurly? Post take away toilet trip? Ring of fire?
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Post by st66 on Aug 13, 2020 18:29:40 GMT 1
No post veg mate to add to your collection for your pop quizzes ect,, it seams to be the prize currancy at the min lol,,,,, ile get you address from my sources lol and ile post you a few as,,, well feeling generous to the coarse ,, ๐๐๐
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Post by st66 on Aug 13, 2020 18:32:07 GMT 1
No iron brew tho mate soz,,,,, made in Scotland from gurrdas,, lol
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Post by jon on Aug 13, 2020 18:33:28 GMT 1
No Jon mate I wasn't being funny so to speak mate re bragging rights comment I just couldn't see why you would change it mate re the decals,, but you can do as you wish mate and I whole heartedly say if you want to yeah just go ahead, it's just an opinion mate I mean you put rz or Rd 385 on it and it will get looks yeah most deff, good or bad I couldn't say but it will have folk talking for deff,,, example you put 350 on her and its fairy fast,,,, sleeper type thing,, or do you advertise it 385 or more and it oh he's done the motor,,, or comments I won't say here,, can you see where I'm coming from mate,, but then again it may not even get a thought mate so it's your bike mate do wot you feel is right mate ๐๐๐ Hi st66, I wouldnโt โchangeโ the decals on a painted bike just because I had I rebored or a long stroke crank. However being unpainted I thought Iโd ask this question. I was originally going to have a single colour decal in the R font saying RD385R. Iโm glad I asked the question as because Iโm considering an RZR paint scheme on my naked R model, I might use that font and have RDR. Who knows the way Iโm going Iโll change my mind again as itโs bound to be a year off paint LOL. Jon
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Post by st66 on Aug 13, 2020 18:36:12 GMT 1
Jon, the penny drops mate I see where your coming from mate,, cool ๐my apologies I presumed it was standard paint already,, ๐๐๐๐๐๐. ANTH
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Post by midlifecrisisrd on Aug 13, 2020 18:41:40 GMT 1
Nothing wrong with an RZR paint job but I'm biased ๐๐๐ Steve
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Post by arrdy350 on Aug 13, 2020 18:43:45 GMT 1
Well mine is at 65mm with a +4 crank so is a 385 ๐ Just donโt put the cc on the bike,,problem solved,,mines not got any Our bikes start off at 347 but are called 350s,so just rounding up Quick question what is a +4 crank? I thought you could only increase the cc by the diameter of the barrel and piston?
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Post by st66 on Aug 13, 2020 18:46:47 GMT 1
I asked the same question a bit back if you do a search 4mm crank it's explains it mate,, basically the con rods 4mm longer,, but have a search the wise ones here explained it much better ๐
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Post by midlifecrisisrd on Aug 13, 2020 18:50:46 GMT 1
CC is calculated by bore size and stroke
If you increase either the CC increases
A +4mm crank is 58mm stroke instead of 54mm
Rods are 5mm longer but that doesn't affect CC. Just reduces side thrust on the piston
Steve
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Post by Tobyjugs on Aug 13, 2020 19:18:54 GMT 1
CC is calculated by bore size and stroke If you increase either the CC increases A +4mm crank is 58mm stroke instead of 54mm Rods are 5mm longer but that doesn't affect CC. Just reduces side thrust on the piston Steve I've forgotten all my technical jargon but it also alters the angle of the dangle between the crankshaft and conrod which can lead to more torque and of course less depending on the angle of the dangle in relation to the expanding gasses on the downward stroke. I think.
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Post by arrdy350 on Aug 13, 2020 19:26:15 GMT 1
CC is calculated by bore size and stroke If you increase either the CC increases A +4mm crank is 58mm stroke instead of 54mm Rods are 5mm longer but that doesn't affect CC. Just reduces side thrust on the piston Steve Ok thanks ๐ hadn't heard of the term +4 crank before.
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Post by jon on Aug 13, 2020 19:28:04 GMT 1
I asked the same question a bit back if you do a search 4mm crank it's explains it mate,, basically the con rods 4mm longer,, but have a search the wise ones here explained it much better ๐ No the conrod could be the same length 110mm, but the stroke is increased by 4mm. Most +4 cranks do utilise a conrod 5mm longer for reasons stated above (like the RD 400, as opposed to LC). This necessitates a piston with 5mm less crown height, and a reprofiled head. Jon
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Post by midlifecrisisrd on Aug 13, 2020 19:46:18 GMT 1
CC is calculated by bore size and stroke If you increase either the CC increases A +4mm crank is 58mm stroke instead of 54mm Rods are 5mm longer but that doesn't affect CC. Just reduces side thrust on the piston Steve I've forgotten all my technical jargon but it also alters the angle of the dangle between the crankshaft and conrod which can lead to more torque and of course less depending on the angle of the dangle in relation to the expanding gasses on the downward stroke. I think. Yes that is correct Was just scratching the surface with the side thrust Less side thrust - more up and down thrust ๐ All to do with the fulcrum Steve
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