Exhaust Bridge and Oiling Holes in Piston

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Dragmeistr

Sponsoring Member

Oct 14, 2002

149

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• Nov 25, 2002

• #1

When doing a top end on my 03 CR 250. I installed a new Wiseco piston. When reading through the paperwork, within the instructions/specs, it said that if you have an exhaust bridge you need to drill oil holes in the front of the piston. Is this true? If it is, why did my stock piston not have these oil holes? The only reason I ask, when I tore it down, this seemed like the only place where the cylinder was starting to show signs of wear(exhaust bridge).

 

RM_guy

Moderator

Damn Yankees

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Nov 21, 2000

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North East USA

• Nov 25, 2002

• #2

I'd drill the holes even if the stock piston didn't have them. The exhaust bridge is the first place you'll see normal wear and any extra lubrication won't hurt.

 

Rich Rohrich

Moderator / BioHazard

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Jul 27, 1999

22,839

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Chicago

• Nov 25, 2002

• #3

Originally posted by Dragmeistr
When reading through the paperwork, within the instructions/specs, it said that if you have an exhaust bridge you need to drill oil holes in the front of the piston. Is this true? If it is, why did my stock piston not have these oil holes?

Click to expand...

Your OEM piston is cast while the Wiseco is a forged piston. The expansion rates between the two pistons are different and the holes are mandatory when running a Wiseco with a bridged exhaust port.

 

D

Dirtvet

Member

Jan 23, 2000

187

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• Nov 26, 2002

• #4

Why would the Wiseco piston not come with holes if they are mandatory??!! It just seems like if they call it a replacement piston for stock it should be ready to go as is. I just ordered one for a 2001 CR 250. Does anyone know if it has this "exhaust bridge", therefor requiring drilling holes in the new piston like the 2003?

 

1

125 rider

Sponsoring Member

Oct 1, 2000

408

1

• Nov 26, 2002

• #5

Originally posted by Tommygun
Why would the Wiseco piston not come with holes if they are Does anyone know if it has this "exhaust bridge", therefor requiring drilling holes in the new piston like the 2003?

Click to expand...

You can tell easily by taking your pipe off, and checking if there is a vertical "bridge" across the exhaust port, or if it is an open hole with no bridge. The Wiseco pistons come pre-drilled for my RM.

 

marcusgunby

LIFETIME SPONSOR

Jan 9, 2000

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• Nov 26, 2002

• #6

Most jap bikes have a bridged port-you Cr im 99% sure has.I guess they dont drill them all, as pistons can fit a variety of bikes and not all need it.

 

D

DEANSFASTWAY

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May 16, 2002

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• Nov 27, 2002

• #7

Ive seen some other builders mill or file a strip to "puddle" a bit of oil on the area of the piston that meets the bridge , it also gives a little clearance at the bridge. The 03 cyl has bridge but the 01 does not it has a wide center exhaust port and 2 sub ports that are on both sides .

 

Y

Yz250rider

Member

Aug 31, 2000

22

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• Dec 2, 2002

• #8

As to your bridge port, do you know if the 02' YZ 250 has it?

 

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DEANSFASTWAY

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May 16, 2002

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• Dec 3, 2002

• #9

Nope but they have one main exh port and 2 side ex ports and the older pistons used to have a hole drilled on that bridge.

 

D

DEANSFASTWAY

LIFETIME SPONSOR

May 16, 2002

1,192

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• Dec 3, 2002

• #10

Not drilled on the bridge but drilled on the piston sort of like if you imagined the piston with the front (exhaust center) at 12 o clock position the holes would be drilled at like 10 and 2 o clock postions .

 

Y

Yz250rider

Member

Aug 31, 2000

22

0

• Dec 3, 2002

• #11

Thank you for your help. This will be my first top end job on this bike. I just bought the top end rebuild kit from wiseco and they sed nothing to me about drilling holes in the piston.This is my first Yamaha and I love the bike to much to mess it up.

 

D

Dragmeistr

Sponsoring Member

Oct 14, 2002

149

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• Dec 4, 2002

• Thread starter
• #12

Well, I guess I answered my own question when I tore the bike down. I did not have enough time to tear it down before I left and drill the holes. When I got back, I tore it down. I would defintely say they are necessary. The only place the pipston/cylinder showed any signs of wear was right in the exhaust bridge area.