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CBR250 valve shims

6930 Views 11 Replies 7 Participants Last post by  ajl14, 
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Does anyone know if Honda supply different size valve shims for the CBR250RR so that valve clearances can be set accurately? If so - where can I get hold of them?
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lordmoonpie said:
Does anyone know if Honda supply different size valve shims for the CBR250RR so that valve clearances can be set accurately? If so - where can I get hold of them?
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Any bike shop should have them, best bet would be to go to a Honda one though, they're a 7.5mm shim available in different thickness.

Some shops are scum when it comes to shims though and will try to charge you like $15 swap fees, bunch of pricks. Last I heard they're about $6 a piece from Honda
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mitchkip said:
Any bike shop should have them, best bet would be to go to a Honda one though, they're a 7.5mm shim available in different thickness.

Some shops are scum when it comes to shims though and will try to charge you like $15 swap fees, bunch of pricks. Last I heard they're about $6 a piece from Honda
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Thanks Mitchkip - I'll give the local dealer a try then! I will need shims as I'm having the cams re-ground for better performance :D
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lordmoonpie said:
Thanks Mitchkip - I'll give the local dealer a try then! I will need shims as I'm having the cams re-ground for better performance :D
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Have you done a dyno run before pulling the cams out to get a before graph to make comparisons to? Will be interesting to see if this actually makes a difference.

also good luck.
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Cams reground.. 10 points for effort I guess.

+1 to getting a benchmark first though :/
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banana.logic said:
lordmoonpie said:
Thanks Mitchkip - I'll give the local dealer a try then! I will need shims as I'm having the cams re-ground for better performance :D
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Have you done a dyno run before pulling the cams out to get a before graph to make comparisons to? Will be interesting to see if this actually makes a difference.

also good luck.
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I'm more interested in what profile/timing/overlap/lift was used, how it was re/ground and by whom.
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Can we get a full write up of what was done and what results you get please?
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banana.logic said:
Can we get a full write up of what was done and what results you get please?
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Well if there's interest in it then sure I'll post up as it happens/ The cams go off today so will be about 4 weeks. There's no chance of doing a before dyno run as the engine was a non-runnign donor. Looked to me like the water pump had seized but everything else appears to be in good order.

The crank is also going off this week for lightening and balancing. I want this motor to hit 20,000 rpm and give me more top end power. I guess it'll be fractions more but I kinda like these interesting "what if" exercises...
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lordmoonpie said:
banana.logic said:
Can we get a full write up of what was done and what results you get please?
Click to expand...
Well if there's interest in it then sure I'll post up as it happens/ The cams go off today so will be about 4 weeks. There's no chance of doing a before dyno run as the engine was a non-runnign donor. Looked to me like the water pump had seized but everything else appears to be in good order.

The crank is also going off this week for lightening and balancing. I want this motor to hit 20,000 rpm and give me more top end power. I guess it'll be fractions more but I kinda like these interesting "what if" exercises...
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Please don't take this as trying to talk you out of doing this.

BUT!

A cbr produces peak power well before 19k redline. The reason that pulling the thing through to redline makes you go faster is because of a lack of grunt down low in the next gear, not because there's a bunch of power to be hard up top. Not much you can do will realistically change that. The reason for retarded amounts of overrev on a racebike is a) because if the thing will keep pulling past 19k in 6th gear (feasible with short gearing) it's extra top end speed, and because if you're just stretching the gear out until a brake marker you're better off to save yourself 2 gear shifts.

Personally, I would be spending my loot on the suspension. Since you're clearly hellbent on doing up the motor (nothing wrong with that, just strikes me as a strange thing to do) I would really be looking to have some kind of baseline before you start on the motor. Otherwise if the thing has wierd peaky power/isn't doing what it should at the end you won't really know where to start looking. Alternately if it produces monumental horsepower you'll never know how much of it was fluke due to a good motor, and how much was your work.

My 2c, looking forward to details.
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Please don't take this as trying to talk you out of doing this.

BUT!

A cbr produces peak power well before 19k redline. The reason that pulling the thing through to redline makes you go faster is because of a lack of grunt down low in the next gear, not because there's a bunch of power to be hard up top. Not much you can do will realistically change that. The reason for retarded amounts of overrev on a racebike is a) because if the thing will keep pulling past 19k in 6th gear (feasible with short gearing) it's extra top end speed, and because if you're just stretching the gear out until a brake marker you're better off to save yourself 2 gear shifts.

Personally, I would be spending my loot on the suspension. Since you're clearly hellbent on doing up the motor (nothing wrong with that, just strikes me as a strange thing to do) I would really be looking to have some kind of baseline before you start on the motor. Otherwise if the thing has wierd peaky power/isn't doing what it should at the end you won't really know where to start looking. Alternately if it produces monumental horsepower you'll never know how much of it was fluke due to a good motor, and how much was your work.

My 2c, looking forward to details.
[/quote]

I hear ya Richo, I guess I have nothing better to do than think about these odd things and have a go. I know there are CBR250RR RC163 replicas out there that rev to 22,000 and if nothing else, that has got to sound awesome through four open megas! :D
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Any news on this yet...?
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Humbug said:
banana.logic said:
lordmoonpie said:
Thanks Mitchkip - I'll give the local dealer a try then! I will need shims as I'm having the cams re-ground for better performance :D
Click to expand...
Have you done a dyno run before pulling the cams out to get a before graph to make comparisons to? Will be interesting to see if this actually makes a difference.

also good luck.
Click to expand...
I'm more interested in what profile/timing/overlap/lift was used, how it was re/ground and by whom.

I would like to see that also. Who does the grind?
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