Rear Head Question

General forum on engines, transmissions, gearing and modifications to each

Moderator: rztom

Message
Author
User avatar
WVWRZ500N
- - - - -
- - - - -
Posts: 967
Joined: Sat Nov 19, 2005 1:15 am
Location: Lee's Summit, MO
Contact:

Re: Rear Head Question

#16 Post by WVWRZ500N » Fri Jun 03, 2016 2:13 pm

silverstrom wrote:
WVWRZ500N wrote: The ONLY engines with corrected compression from the factory was the 1986. I've built two 1986 engines.
That's interesting, because the part numbers for the 86 heads are the same as the part numbers for the 84 heads. They changed in 85 but for the S model went back to the 84 #s.
Microfiche has been known to be incorrect before. I'm only referring to hands on verification.
Regards,
Bill Wilson
Wilson Performance
Lee's Summit, MO
http://www.wilsonperformance.net
Member RZ500 Owners Group #573
816-377-3185
WVWRZ500N@aol.com

silverstrom
- - - - -
- - - - -
Posts: 3238
Joined: Sat Feb 04, 2012 7:36 am

Re: Rear Head Question

#17 Post by silverstrom » Fri Jun 03, 2016 7:04 pm

WVWRZ500N wrote:
silverstrom wrote:
WVWRZ500N wrote: The ONLY engines with corrected compression from the factory was the 1986. I've built two 1986 engines.
That's interesting, because the part numbers for the 86 heads are the same as the part numbers for the 84 heads. They changed in 85 but for the S model went back to the 84 #s.
Microfiche has been known to be incorrect before. I'm only referring to hands on verification.
That's true. I have a hard copy 86 S parts manual from Yamaha and it is the same as the microfiche.

The more I talk about this the more I'm convinced it really doesn't matter. I haven't seen anyone else bring up the subject and it seems 99% of the owners don't know about it and have been using whatever heads they happen to have. Anyone doing a performance build, like yourself, will cut the heads anyway, so again, it doesn't matter.

I was looking for something conclusive to state why there are differences and what those differences/changes accomplished, if anything. So far we're where we started. We know there are differences, but no definitive explanation from Yamaha's literature. I was hoping it would be as simple as it is with 350 heads. No such luck.

vma500
- - - - -
- - - - -
Posts: 668
Joined: Thu Jan 26, 2006 3:56 pm
Location: la belgique
Contact:

Re: Rear Head Question

#18 Post by vma500 » Sun Jun 05, 2016 7:28 am

i checked some spare heads too , they also have the step on the front ,no steps rear

btw ... are u using stock pistons ? coz they differ in height also ...if i remember well it was 0,4 mm that the lower pistons are shorter ,so to equalise everything u need to mill the front ones extra
my bikes :RD500 2X ,RD 350 F2 , RD 350 31K,RD350 4LO,RG500,RG250 WW,RGV250,TZR250 3MA,TZR250 3XV,NS400r,NSr250 mc21,KR1250S,

Post Reply