Topic: Camshaft bearing clearance ?

[wrenchmuch]

I've been rebuilding my 750 k1 engine and I've got most of it back together now and I'm about to start degreeing the camshaft . I set up #1 to use putty to check my piston to valve clearance and it looked like the clearance on the inner two cam bearings were a lot bigger than the outer two .
                  My cam holders measure
       1                     2                     3                      4               
  .8672               .8671               .8673                .8678                   Honda spec new .8669-.8678       Limit  .8701
                  My camshaft measures
  .8643               .8577               .8581                .8638                   Honda spec new  Center journals: .8578-.8587     Limit  .8559         New Webcam #41
                                                                                                                             End journals:      .8637-.8646     Limit  .8628
                   Clearance
   .0030               .0094              .0092                .0040                           Honda service limit .0083

 Holder and camshaft measurements seem to be within spec but the center clearance is not . Why make the middle journals smaller .
Thanks to all who've help me so far  Mike

[wrenchmuch]

Anybody ?? Anybody??

[City Boy]

Just a guess wrench but maybe it is caused by the load imposed by cam chain.  Rock On

[bryanj]

Seen that before, as long as the journals and bearing surfaces are smooth and not graunched up just fit it and run ----you will have no problems

[MRieck]

Seen that before, as long as the journals and bearing surfaces are smooth and not graunched up just fit it and run ----you will have no problems

Yes....I've seen it many times too on many different engines. To tight can be a problem.

[wrenchmuch]

Thanks for the replies . I can see the light at the end of the oil passage now.

[AshimotoK0]

Hi - I have similar measurements to this original post on my K0 cam but my lift is less than the service limit in the manual

Typical measurements are:

1.1050"  Base Circle   -   1.4095"  Inlet Cam measurement   -  lift = 0.3045"  (limits in manual 0.3122)

The cam surfaces are all unmarked and the base circle is within tolerance in the manual.

If I use this cam then how will it affect the running of the engine?

[HondaMan]

I've been rebuilding my 750 k1 engine and I've got most of it back together now and I'm about to start degreeing the camshaft . I set up #1 to use putty to check my piston to valve clearance and it looked like the clearance on the inner two cam bearings were a lot bigger than the outer two .
                  My cam holders measure
       1                     2                     3                      4               
  .8672               .8671               .8673                .8678                   Honda spec new .8669-.8678       Limit  .8701
                  My camshaft measures
  .8643               .8577               .8581                .8638                   Honda spec new  Center journals: .8578-.8587     Limit  .8559         New Webcam #41
                                                                                                                             End journals:      .8637-.8646     Limit  .8628
                   Clearance
   .0030               .0094              .0092                .0040                           Honda service limit .0083

 Holder and camshaft measurements seem to be within spec but the center clearance is not . Why make the middle journals smaller .
Thanks to all who've help me so far  Mike

This is typical, actually. Even on engines I tore down "in the day" the center two journals had lots more clearance than Honda's spec. Honda talked about a service limit of .0083", but .006" seems to be brand new. Sometimes the aftermarket cams come with larger inner journals than Honda's own, it you are concerned about the numbers. Truth is, the center of the cam flexes quite a bit, due to the long, thin design, and it has never been a problem for the engines.

My own K2 for example, has .0112" on on of those inner bearings and .009-ish on the other. In terms of performance, this means there is late opening of the intake and exhaust valves in cylinders 2 & 3 when the cam pulls downward during hard acceleration. This makes for some engine vibration, which usually goes away when the acceleration is over and the engine is running at a steady speed.

A new clearance spec is .0042", but I have NEVER seen one with this little clearance, once the engine had 10,000 miles or so. The typical minumum is around .006".

But then, I haven't worked on every 750 engine out there, either... 

[AshimotoK0]

Thanks Hondaman. Your post tells me about the centre bearing clearance but how about my concerns about the cam 'lift' in my posted reply of today. Thanks for all of your advice BTW

[HondaMan]

Hi - I have similar measurements to this original post on my K0 cam but my lift is less than the service limit in the manual

Typical measurements are:

1.1050"  Base Circle   -   1.4095"  Inlet Cam measurement   -  lift = 0.3045"  (limits in manual 0.3122)

The cam surfaces are all unmarked and the base circle is within tolerance in the manual.

If I use this cam then how will it affect the running of the engine?

I'm afraid Honda's manual only referred to the sandcast K0 engine's cam. None of the others ever had as much lift (or duration!).

Typical inlet lift on K1 through K3 engines was in the range of .303"-.311", in my experience. It seems that the base circles were often pretty large, probably to reduce the wear the top ends were experiencing in heavy city traffic situations, and Honda just sort of "delta tuned" the part without changing any published specs.

The most interesting part: the Honda manuals say that 1.411" is the wear limit for the inlet: after the early K0 version, I seldom saw a NEW one with this much overall height. My own 750 had 128,000 miles on it when I last measured it: the overall height average was 1.388", yet with no score marks nor concaved rocker feet. The hardening must be pretty deep!

It's still running fine, except it won't pull past 8700 RPM anymore: Terry in AUS sent me a cam with about 8k miles on it: someday I'm gonna put that in and pretend I'm going racing again. 

[AshimotoK0]

Hey Thanks Hondaman - I was just about to junk my cam and bearing carriers until I read your comments!!  Seems I would have been chasing elusive replacements which I may never have found. Are there any other critical measurements of parts within the engine which I should be aware of when looking at the specs in the manual?

[HondaMan]

Hey Thanks Hondaman - I was just about to junk my cam and bearing carriers until I read your comments!!  Seems I would have been chasing elusive replacements which I may never have found. Are there any other critical measurements of parts within the engine which I should be aware of when looking at the specs in the manual?

Ummmm...much too long to list here. I kinda got tired of doing that in the past, so I started this "book" thing. I hope to get it done soon: the engine building season is coming! I do have a publisher, at least...it will get announced here when I get past the "taking more pictures" stage (1150 and counting...)

[AshimotoK0]

Good on you Hondaman - I was only thinking to myself that all your knowledge should be in print.

I had my paintwork (excellent job) done by a guy who has the workshop next door to the UK guru John Wyatt who wrote one of the original CB750 restoration guides. Never seen a copy and it's out of print I think. But copies go for big bucks on Ebay, so can't think why he doesn't reprint it.

A book specifically on the engine would be great though - power to you - all 67 of them!!

and thanks again  for all of your kind help.

I think my main questions on the crank have been well covered here anyway.