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600cc crank end float

Submitted by graham_bingham on Tue, 16/01/2024
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Hi,

I have a '48 ES2 which is fitted with what I am told is a '57 600cc engine (19S?) the engine number is 74583 M9.

I'm after a little help regarding crank endfloat. The saga started when I replaced the primary chain housing oil seal. Whilst I had the cover off I turned the engine over and noticed that the primary drive sprocket was spiralling in and out as the engine went through its combustion cycle. I stripped the engine and found that the endfloat on the sprocket end of the crankshaft was 50thou when the piston was at the bottom of the cylinder. Nil whilst the piston was half way and 10thou at the top of its stroke. These measurements were taken with the oil pump and spiral drive in situ.

When I removed the oil pump and drive I was able to measure around 50thou anywhere in the combustion cycle. It seems that the oil pump drive is determining the endfloat. the spiral drive cog on the oil pump has some wear marks in places presumably where it is running tight in mid stroke?

I want to set the crank enfloat up to the specified 5 to 8 thou but I'm puzzled where to start without putting a lot of stress on the oil pump drive.

Can anyone help please?

many thanks in anticipation

Graham

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PXL_20240102_170903574.jpg

Submitted by david_cooper on Tue, 16/01/2024

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Not an explanation but the oil pump cannot restrain end float.  The pressure between the helical gears does provide an end thrust in one direction when it is running.  If engagement between teeth is tight, might it perhaps reduce the ease with which you can move the crank?  Is the crankshaft slightly bent, or gear slightly eccentric?

Submitted by jonathan_newton on Tue, 16/01/2024

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Thou that is….   ( minimum to make up to correct).  As David advised the oil pump cannot control the end float as it just rotates on the worm. If the variation still happens when the oil pump is off it’s something else that is kicking the crank.  The fact that you have that amount of float means it needs further inspection. If the pump is affecting the float movement cyclically it could well be that the pump shaft is bent or the pump gears fouled.  Feel the turn over torque of the pump, does it have a tight spot? Regardless your next step is to split the cases and find where the wear is and what the possible cause is.

cheers

J

Hi Jonathan,

Thanks for answering my question. How tight should the oil pump drive be? I tried to turn mine today and could only just turn it with my fingers it seems quite stiff.

I am splitting the crank cases tomorrow and will also have a look inside the oil pump

Submitted by jonathan_newton on Wed, 17/01/2024

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.. is only a series of gears. There should be a nominal but constant load when you turn it.  The pump may have ingested something and bent the drive  

open it up and it will be clear what has happen..

cheers

jon

 

Submitted by graham_bingham on Fri, 19/01/2024

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As I mentioned before the oil pump was difficult to turn with the fingers. as soon as I started to loosen up the four bolts holding it together it freed up. It looks clean inside with no obvious damage but it has heavy score marks in the base plate where it has been running tight (see photo).

I noticed that the club shop had a "cleaned and lapped" pump for sale so I have ordered that.

As for the crank shaft excessive end float (50 thou) on splitting the cases I found that whoever had the engine apart last obviously didn't bother setting end float as there were no shims present at all. The bearings seem to be in good order with no obvious play so I have ordered shims to set it up correctly.

The bike was running well before I noticed the end float problem so I'm hoping that attending to the pump and setting the end float will be a good preventative measure.

Thanks for your help

Attachments
PXL_20240119_102609581.jpg

 


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