rbsdsu

Member
Mar 1, 2004
8
0
1st off I am a newbie to this site and I would like to say hello, I am Ryan and I live in So Cal and I ride as much as possible!

That being said, I have a buddy who has a YZF 400 that has lost almost all compression, I can not find TDC and when you do kick it over you get nothing or maybe a backfire... So we tore it down the other night to find that the cams and valves were all fine upon going deeper I found what I hope to be the problem! The cylinder wall which has that plating on it has been completely worn of in 2 distinct areas and I can feel some pretty good gouges with my finger nails. My initial impression was that these are extremely high compression engines and that must be the cause.... I hope! Anyways I was just hoping to get some back up on my diagnosis. Does anyone know where I can have the plating re-done, 2nd would it be a good idea to have a new piston and ring set to install???

I appreciate all of the info you guys offer

Thanks...
 

Rich Rohrich

Moderator / BioHazard
LIFETIME SPONSOR
Jul 27, 1999
22,816
16,885
Chicago
Is the wear on the exhaust side of the cylinder?
 

rbsdsu

Member
Mar 1, 2004
8
0
Rich Rohrich said:
Is the wear on the exhaust side of the cylinder?

I'd have to go back and look to see what side the wear was on. Would a particular side denote a specific problem????
 

Rich Rohrich

Moderator / BioHazard
LIFETIME SPONSOR
Jul 27, 1999
22,816
16,885
Chicago
Short skirt slipper pistons like this tend to show the majority of their wear on the exhaust side thrust face of the cylinder.
 

SFO

LIFETIME SPONSOR
Feb 16, 2001
2,001
1
If it is a well ridden 400 it is a prime candidate for a full rebuild.
A good valve job with new springs and seals along with a piston and a replate would be a bare minimum.
I would seriously consider rod replacement and cam chain as well.
Early thrashed 400s have the habit of shedding the small end of the rod.
This ruins everything.
 

Rich Rohrich

Moderator / BioHazard
LIFETIME SPONSOR
Jul 27, 1999
22,816
16,885
Chicago
SFO said:
Early thrashed 400s have the habit of shedding the small end of the rod.
This ruins everything.

... and they end up looking like this :ohmy:
 

Attachments

  • t2.jpg
    t2.jpg
    35.7 KB · Views: 57
  • t3.jpg
    t3.jpg
    22 KB · Views: 53

SFO

LIFETIME SPONSOR
Feb 16, 2001
2,001
1
Just think, parts from that very motor went on to be part of a bike that won an AMA national event last year!
 

Rich Rohrich

Moderator / BioHazard
LIFETIME SPONSOR
Jul 27, 1999
22,816
16,885
Chicago
SFO said:
Just think, parts from that very motor went on to be part of a bike that won an AMA national event last year!

The cosmic circle of racing life :aj: :yeehaw: :aj:
 
Top Bottom