Topic: Rod ends?

[MattFreeman]

I'm not sure if I'm going about this the right way so I'm open to all input

First off, I'm having trouble reading the bearing markings on my crank so I am trying an alternative method to the "color chart".

I'm using a telescoping gauge to measure the rod end and measuring the crank in the hopes that I can figure mathematically which bearing will give the correct tolerance. I've gathered that this is possible, no?

So the problem I think I'm having is that when I measure the crank end of the rod. I torque the rod closed and measure at three points. If inline with the small end is 12 o'clock, I get 1.5385 at 12 o'clock and 1.536 at both 2 and 10 o'clock. Is this going to be a problem? My friend told me that automotive rods get reconditioned by shaving the cap and re-cutting the "hole". Is this done to our rods (cb750f1)? Is .0025 enough to worry about? If the discrepancy is allowable which measurement should I use?

As always, thanks in advance.

On a side note, when removing cylinder studs is penetrating lube helpful?

[754]

I would not rely on telescopic guages to measure rod bores.


 They should be marked...

[MattFreeman]

They are marked, my 20/20 can't read them.

[bryanj]

In the factory they used "air gauges" to measure the size and you will not get anywhere near as accurate with mechanical means. Rods can go "Oval" but usually ony if a big end has been knocking and whilst a low stress car rod can be re-sized it is not good practise with a bike one.

If you cant read the numbers try scanning the side of the rod to the computer then blow up the picture---works for small capacitors!!

[MRieck]

I would not rely on telescopic guages to measure rod bores.


 They should be marked...

That is for sure.

[MattFreeman]

So lets say I can use the color chart to figure the bearing size, and the size discrepancy was detected by the most accurate means, is it acceptable?

[bryanj]

No use plastigaige

[MattFreeman]

No use plastigaige

OK.

Is it OK that the rod ends are slightly oval.

BTW they measured round with the bearings in.

[bryanj]

I suspect the ovality is a slight discrepancy in measuring, try the plastigauge at 2 or 3 points but not where the "Join" is. I have before now on both 750 and 500 fitted all of the tightest tolerance shells and run the engine in very carefully for 3-5,000

[MattFreeman]

I suspect the ovality is a slight discrepancy in measuring

I'd agree that this is a possibility if it weren't for the fact that I can get exactly the same measurement using the same method at three different points on the same rod with the bearings in.

At this point I would like to get past my method and get some input as to whether or not a rod end being .005 out is tolerable.

[bryanj]

A rod end 5 thou oval i would say is NOT acceptable if you are measuring in inches, are all the rods the same or is it just one?

[MattFreeman]

Yup inches. They all have some but not equal discrepancy.

[bryanj]

I must admit to never having bothered to measure ovality on Honda rods as if an end goes its a new crank with rods anyway cos normaly the shells weld to the crankpin and spin in the rod wrecking the surface so on the very few times it happened we just got a used crank with rods.

Some 72ish UK 750's had bad oil hoses which restricted the oil flow to the pump which knocked out the big ends but they were all done under warantee and very quietly by main dealers so nobody knew exactly what was changed.

Sorry cant be more help, if it was running OK before you stripped it and there is no sign of bearing surface damage i would put it back together as is, sometimes too much knowledge of what is in there is worse than not enough

[754]

There is only a few sizes.

 Clearance depends on how you ride it, can be a tad looser if you run it real hard and expect teardown in near future.

 If you want it to last as long as possible, set it up properly and run it in nicely.

 I can see it having .0005 oval, but not .005