Topic: 550 Oil pump o-ring again...

[billstron]

I know this is a well worn topic, but I have done a search and haven't found my answer.  What is the size of the o-ring under the oil pump cap in a '78 550?  You know, the one that Honda doesn't sell any more.  Thanks. 

[Klark Kent]

this post is the one i remember stating the size, but it seems to contradict itself about whether you need the 47mm or something "in between 45 and 47mm."  if you are unsure (or even if you think you are sure) its the oil pump gaseket, my leak was actually coming from the pressure sensor diaphram and looked like it was the oil pump gasket or shifter seal at first glance. 
good luck
-KK

[billstron]

I believe ALL of those things have been leaking.  At least at one time I thought that... because I have replaced them all   First is was the oil pressure sensor.  That was really f--ed up, I could watch oil come out of it.  Then it was the shifter seal.  Not sure if it did anything but take time.  Most recently it was all of the other oil pump seals.  I believe the leak lessened.  The last thing that I know to change is the cap seal.  Anyway... might as well finish the job, right? 

[Kevin400F]

When I re-did the pump on my '76 550, I used 2mm cross-section by 46mm ID.   

I have some extras, shoot me an e-mail off list if you would like me to drop one in the mail to you.  Material is BunaN, 70 Durometer.

Kevin Hunter
kthunter01@sbcglobal.net

[billstron]

Kevin,
PM sent...

[crazypj]

If your blowing the top off the oil pressure switch your running too thick an oil and/or revving it too high when cold, before the oil thins out.
Been there, broke that ( did 4 under warranty  ) I have not broken one since I  found out what I was doing wrong
PJ

[billstron]

I never even thought of that.  What grade oil did you switch to?  I run 10w40.