Vintage Dirt Bike Q & A

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PostPosted: Thu Oct 11, 2012 8:38 pm 
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Joined: Mon Oct 08, 2012 2:27 pm
Posts: 5
well now it all makes sense lol :) the 2nd over size is marked right on top of the piston 80.50 its a single ring for the MX version of the RT1 if it will help you let me know and I will try and find the ring tomorrow


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PostPosted: Fri Oct 12, 2012 7:36 am 
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Joined: Tue Aug 31, 2004 1:44 am
Posts: 283
Location: Maysville, AR
Viking 8 wrote:
I have a 1970 Yamaha rt1 360 that has a wiseco 184p2 piston and the piston I have in it is cracked that is why I am looking for a wiseco 184p2 piston


if your bike cracked a skirt it is time to have the cylinder rebored and go to a larger oversize.

the piston when a engine is too loose rocks back and forth and it makes a rattle sound when the engine is running and this takes out the skirt on the piston.

sounds like you need a top end job done.

if it were me i would get it bored to the next oversize or 2 oversizes to clean up the bore and rid it of all the cylinder taper and replace the wrist pin and bearing and with new seals and gaskets.

if the crankshaft seals are suspect i would replace those too if needed.

this is a boring shop i know of as i would not trust anyone in my area to handle it but if there is a good place locally that is good you can use them too.

this is the place i can recommend.http://www.billbune.com/

most places locally in my area bore it out too much and there is too much clearance and the engine piston slaps as a result.here is a video on a 1971 Yamaha DT1 that was in dire need of a top end job.click the image to play the video.
Image

i ran across this when the guy complained it would not rev and when i heard the piston slap i told him he needs a top end job badly,a story a little shorter he sent the cylinder to Bill Bune and had it bored and and fitted with a bigger over size piston and he also replaced the wrist pin and bearing.he buttoned it up and the engine is much much quieter mechanically and it also has a lot more power than it did and it revs up cleanly.the bike is a 1971 Yamaha DT1E 250.

Bill Bune also stocks pistons and he may have one if needed if you cant source one to send out with the cylinder.

_________________
(2) 1968 DT1 1970 RT1M,1970 DT1C 1971 RT1B Enduro 1974 MT250 1974 DT250A (2) 1975 DT400B 1974 DT100,1978 DT175
1975 CR250M1 1979 CR250R 1979 Kawasaki KZ400H1 Jesus is Lord!!


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PostPosted: Fri Oct 12, 2012 7:51 pm 
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Joined: Sun Jun 10, 2012 9:12 am
Posts: 7
the class I race my bike in has a bore size the max I can go is 80.50mm with the stroke I have I had nik. added to my jug so I dont need a bore shop I am a motor builder and the cracked piston is fixed with nik. not I need a WISECO 184P2 piston and it is an 80.5mm piston this bike flys with the porting and pipe I have now I just need this Piston to get me going again


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PostPosted: Fri Dec 07, 2012 6:37 am 
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Joined: Thu Dec 06, 2012 11:17 am
Posts: 4
In the 70's I was doing a lot of port work and other upper engine mods for the local Yamaha dealer's pool of customer/racers. Severeral years into this the Wiesco pistons first showed around here. I don't know if was a new product, or people just became aware, but in any case, we had a LOT of problems with 'em cracking on the skirts. With the V6 Mercury racing outboards of today, some of which approach 350 horsepower from 2.5 liters there are still issues with Wiescos and many people refer to them as seizeco. Personally I won't run 'em in a bike or a boat.

One other thing I'm curious about is the comment on adding nico to the cyl. Does this mean the steel sleeve was plated with nicocyl? I've only seen this on alum cyls with no steel sleeve and wonder if it lives.


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