re-bore time?

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Gary66
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Joined: Sun Jan 05, 2014 10:53 am

re-bore time?

Post by Gary66 »

Hi guys. I whipped the old 380 out at the weekend for a bit of man cave time. For a while now i have felt it seams a little "lame" when kicking it into action (this may not be the case at all but kicking the x7 into life seams a lot harder, i assume its because its 3 cylinders as apposed to 2) I have ordered up a compression tester so will check this. So if its low is it a case of just new rings or a re-bore? i ask as i have never just changed the rings and wasnt really sure if its really an option at all
Thanks for any help received Gary
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Alan H
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Location: Wombwell, Republic of South Yorkshire

Re: re-bore time?

Post by Alan H »

Could be anything really. First, remember that a 380 is 1.5 X a 250 as the bore/stroke is the same, the 380 is lower compression too and lower horsepower compared to the 250/380 engine size ratio (I only have details for the early models, but the 250 was about 30hp, the 380 about 38hp).
It may just need a good decoke (especially the baffles and exhaust ports), plugs and timing checking, air filter cleaning.
I'd go for the cheaper options first! You can always check bore/piston size and wear when you get the top end on the bench.
Another 'performance upgrade' that has been tried on the 750 especially, is to fit a relay in the ignition circuit so that the coils get full battery voltage instead of what can get through long lengths of wiring and lots of old and duff joints between battery, ignition switch, cutout switch, coils and points.
Better voltage there gives better performance and easier starting too.
Also remember that the 380 was more of a tourer than the 250, and was more torque-y so you might be expecting a tad more than it can give.
Proof that four strokes are over complicated
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Gary66
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Re: re-bore time?

Post by Gary66 »

To be fair Alan you're probably right, the x7 is on fresh pistons and bore so still nice and tight kicking it into action. I will check as you have suggested, what's the score with the relay? Ie how and where is it fitted etc
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Alan H
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Re: re-bore time?

Post by Alan H »

There's been a few post about this subject, but typically I can't find them!
Basically, the orange wire from the right handlebar stop switch that goes to a multiplug under the tank needs cutting a couple of inches from tbe multiplug. Put a male spade connector on it and put that on one side of the relay 'coil' connection. T'other side goes to earth. With ignition 'on' and kill switch 'on', the relay should click, and 'unclick' when you use the kill switch or ignition switch. Now get a 15a fuse and carrier, wire this direct to the battery + with the fuse close to the battery. T'other side of the fuse goes to the relay contact terminal. T'other relay contact terminal goes to the orange wire that you cut earlier, so now when you do the clicky bit mentioned earlier, the full battery voltage will go to the coils rather than about 10 volts as originally. More volts there means a stronger spark at the plugs. Make sure that the battery earth wire connections are clean too. I suppose I ought to get a relay and do a diagram too, and sticky this somewhere, unless it's already been done.
Proof that four strokes are over complicated
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itsnotateapot
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Re: re-bore time?

Post by itsnotateapot »

This is how I did the relay mod I didn't have to cut any wires this way.
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SUZUKI GT750 L 8-)
SUZUKI T500 M 8-)
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Suzuki T500 Cobra 8-) 8-)
Suzuki GTS 500 Hybrid.
Suzuki RG250.
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Gary66
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Re: re-bore time?

Post by Gary66 »

Thanks Richard that helps
barney01
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Location: Prestatyn.Wales

Re: re-bore time?

Post by barney01 »

Dont know where i got it but here is another picture
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relaywire.jpg
NO SMOKE .......NO POKE
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Gary66
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Re: re-bore time?

Post by Gary66 »

Ok guys, the compression tester arrived today so i got to it, checking each cylinder. All 3 read 100psi +1 -1 ish. Is this a tad low? If its low what next, would de-coking the exhaust port help at all as Alan suggested? Not overly concerned but i do have some "bike dosh"on one side for a re-bore if required before the weather finally picks up :tw
Any help greatly appreciated
Gary
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Gary66
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Re: re-bore time?

Post by Gary66 »

So i have had a quick google of this. Would i be correct thinking that the rings can become gummed up in the grooves due to carbon build up, therefore doing a de-coke frees them off for better sealing in the barrels? If this is the case is it a simple case of whipping off the head and barrels and cleaning up the gummed up grooves, obviously measuring the bores/rings etc once they are all visible for signs of wear
Cheers Gary
barney01
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Re: re-bore time?

Post by barney01 »

Gary, first thing to note is that compression testers vary in readings it really depends on how much you spend on the gauge! However i think its more important that the readings are of similar value. With regard to the rings, they are supposed to move during normal operation and yes they can stick in the grooves. I would definately clean the piston crown and exhaust ports as well as cleaning those grooves. A new set of base and head gaskets would make it a good job too. You can using your fingers feel the inside of the bore at the front and top of the stroke see if there are any ridges. If there are then it may be time for a rebore.
Another way is to remove the piston rings insert them into the bore and measure the gap between the ends of the rings at the top, centre and bottom of the stroke.
NO SMOKE .......NO POKE
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