Wyldkat
Nitrous Nuisance
Joined: 10 Apr 2011
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MarJay
But it's British!
Joined: 15 Sep 2003
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cb1rocket
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MarJay
But it's British!
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Teflon-Mike
tl;dr
Joined: 01 Jun 2010
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 Posted: 16:35 - 22 Jun 2011  Post subject: Re: Would you...? Re-bored Cylinder Head |
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| Wyldkat wrote: | I've just picked up a load of parts for my GP100, included was a re-bored cylinder head.
Can't remember of the top of my head what the original size is but this one is 50mm dia.
Looks quite neatly done to be honest (I mean, I'm no expert but I know what to look for - scratches/grooves etc)
The outlet holes aren't damaged or anything either which is a bonus....
So, he tells me that this would take it upto the equivalent of a 150ish....what would you guys advise - put it on (obviously with an oversized piston) or sell it.
OR
If anyone wants it, PM me |
As Marjay, I think you mean the 'Barrel'. I dont know what the 'quoted' bore diameters are for the GP100, 'classic' dimensions for a 125 are 54x54 for a 123cc displacement. That's the original dimensions for the DKW RT125, and has been carried through most two strokes, since. Believe that the DT125 single is still 54x54.
50x50 would give you 98cc, and 50x56 would give you 123... so would seem about 'right' they have shrunk the classic dimensions to 50x50, keeping the engine 'square' to make a 100cc bike, then over bored to make it a full 125 again.
How accurately are you measuring the bore diameter?
Over bores tend to go up in 1/4mm increments.... measuring with a vernier, I'd not be confident my readings, all round, up and down the length of the bore could be THAT accurate....... with a steel rule? No chance.
Could still be rebored, maybe just one size over. Or may have just been 'honed' to take over size rings on stock sized piston.
IF I needed a barel, I'd think hard about it, and depending, I'd either try a stck size slug and 'see how it goes'... or take barel round to my local freindly machine shop, and bung them a fiver in beer money, to 'clock' it for me and tell me what sized piston to buy... fiver, to be sure, is cheaper than a new gasket set, or a new piston, if I made the wrong guess, and certainly less than the cost of a rebore if I discovered the mistake the hard way!
alternatively, if I wanted to hog the bike out a bit...... I'd check available piston sizes. and the amount of metal in the liner.
The barel castings will be the same whether made up for 1000 engines or 125's. They may even shrink the same liner into them, and the final part is only differnt by dint of how big a hole they bore down the middle..... in which case, could bore it to take a 125 piston..... alternatively, if they curt the hole in the casting larger to fit a bigger liner to make 125 engine, could be you run out of metal in the liner before you make a hole big enough to take the 125 piston.
Bit more measuring, then a word with same machine shop...... tell them to put a hole down the middle to suit whatever piston I chose.
Rebore is 'about' £30 ish..... if you ask them to take it out a few over sizes, they may charge you a few quid extra.. but normally not much.
But, as it stands, if I need to get a piston to match it, that's the safe way... get it rebopred ANY WAY and eliminate a variable.
Meanwhile...... sounds like standard 100 barel, and either stock sized, or close to first over bore size.... BUT given the tolerences here, we REALLY cannot say from a number to the closes mm..... especially not knowing how measured.
Just checking, 50 dead gives 98.1cc, first over bore at 50.25, would give you 99.1cc, second over bore at 50.5, would give 100.1cc.
56mm 125 piston gives 123.1cc, 1st O/B at 56.25, gives 124.25, 2nd O/B, 56.5, gives 125.3cc
Because of the short stroke, you'd have to go out to 62mm to get 150cc... thats a HECK of a long way on a little engine!
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My Webby'Tef's-tQ, loads of stuff about my bikes, my Land-Rovers, and the stuff I do with them!
Current Bikes:'Honda VF1000F' ;'CB750F2N' ;'CB125TD ( 6 3 of em!)'; 'Montesa Cota 248'. Learner FAQ's:= 'U want to Ride a Motorbike! Where Do U start?' |
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Wyldkat
Nitrous Nuisance
Joined: 10 Apr 2011
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| Posted: 09:20 - 23 Jun 2011 Post subject: |
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Ok, I really should think about how stupid these questions sound to you guys 
Well, I'm thinking I probably wont take a chance anyway so it's going on ebay.
Theres nothing wrong with the one on there now so why risk it?
Cheers for 'advice'/subtle criticism  
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Oldie - 1987 Suzuki GP100 SOLD!
Current (as of 12/7/12) 2001 Honda Varadero 125 |
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hmmmnz
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