yep thats true, Wisco are forged and they have there own specs.

Can anyone tell what the original piston size is for a DT 400b please 

 

85mm std. 85.25 first over etc .50-.75-1.0=86mm
Actualy in hindsite i guess talking the piston only the std one is a gnats whisker under the std size & might have 96 on to but now i'm lost--help someone? fraction of a fraction. Or it it .04 [difference between 96 & the full size. Na don't follow me. I'll go measure a typical piston now & get back.

Ok, found a std 360 80mm piston with 96 on top & measures 79.88mm. So how's that pan out? is the 0.12mm close to 5 thou if bore to 80mm. So would bore it slightly under 80mm to get the right clearance. Sorry if i'm stiring the pot. I failed maths at school. Ok i'll go find an oversize piston now if i can. But i guess you don't go sending the cylinder without the piston to get bored to the oversize.

Ok, only first over i have is a yz400f @ 82.18 being an 82.25 piston [.25 on top] so 82.18 to 82.25=.06mm = 2.4 thou[in my head?.
Which might be slightly more than yamaha say for clearance without researching.
In saying that, with the YZ big cutaway yamaha used to give a calculation between what you measure to give you the imaginary actual clearance as if there was a full skirt.
I can only measure right where the cutaway ends. & by memory the 360 or 400 with windows you measure across at the top of the windows & the size stays the same from bottom up to that point then quickly tapers from there on towards the top.
Man i love confusing you guys.
Or am i just bamboozling myself more-likely haha.

Thanks guys .. I think so if my piston is 86. Can I get a 86.25 piston n why would anyone get a new bike and bore it out so far considering the bikes only done 4 thousand miles with a 13toothed front sprocket ?.. mind it's come from Colorado so that could explain a thing or two

Oh blimey, 86 is 4th over in yamaha speak. Must've been some terrible stuff going on to need to go out that far. Maybe someone thought one more mm might give it lots more horses. That's a shame. Wiseco might go past one mm but generally they go up in half mm steps.

Thanks RT yes they do a 86.50 for £160.. just dropped jug off see if it can be honed out if not it'll be a resleeve or another jug as for a good one they're about the same price here in the UK