Opening up crankcase mouths

[Indiana jones]

Is it possible to open up the crankcase mouths to accept 1250 jugs on the bench with some careful die grinding?

[Pat Conlon]

Yes.
I recall several years ago someone posting they did their work by hand....
Wait for the experts to chime in....

[Indiana jones]

 I did a bit of searching and came across a thread from a few years ago about an Fj build with some very long winded posts.
Some very suspect methods were employed throughout the build, which included opening up the crankcases with hand tools.
Things didn't end well and there was no mention of any issue with the shaving work that had been done but there were so many other issues, I doubt it would have been noticed.
I'd just like to know if someone competent has done it with successful results.
I'm in Ireland, so finding someone to do this work is impossible and sending to the UK is out of the question with their brexit fiasco.

[JMR]

 I have done it on CB750's and early GSXR's. Use the new, larger base gasket with some Dykem and a scribe to outline the upper case.

[racerrad8]

There have been posts of people doing it while the engine is assembled, but I have never done it that way. There is just no way of keeping the shavings out of the engine.

I've also seen gut put complete bottom ends into a solvent tank and "flush" the engine clean.

I have the upper case machined with a fly cutter when disassembled.

Randy - RPM

[JMR]

There have been posts of people doing it while the engine is assembled, but I have never done it that way. There is just no way of keeping the shavings out of the engine.

I've also seen gut put complete bottom ends into a solvent tank and "flush" the engine clean.

I have the upper case machined with a fly cutter when disassembled.

Randy - RPM

That is my general standard operating procedure indexing the case off the cylinders. I have never done this operation....by hand or mill.....on an assembled bottom end......that would be foolish.

[fj1289]

I'm shocked anyone would do this without splitting the cases!

[Pat Conlon]

I don't think that's what Indy was asking....of course you would split the cases and empty them out, no question, I think he wanted to know if you could do this procedure by hand (die grinder and carbide tip) or do you need to use a boring machine for the fly cut?

[Indiana jones]

I don't think that's what Indy was asking....of course you would split the cases and empty them out, no question, I think he wanted to know if you could do this procedure by hand (die grinder and carbide tip) or do you need to use a boring machine for the fly cut?

Cheers Pat. I have split and empty 36Y cases on my bench.
I can see no reason why a steady hand and paitence couldn't achieve the required result when it is the only practical option.

I'll make a few phone calls to some engineering shops, I might be surprised.
Motorbike engines are not their thing and they usually refuse to work on them.
Granted, this should be pretty risk free.
All previous work like this was a simple case posting it to the UK, not an option anymore due to duties and taxes charged on both legs of the journey.

It's a nightmare.

Some metric figures for the openings required would be great.

[fj1289]

I don't think that's what Indy was asking....of course you would split the cases and empty them out, no question, I think he wanted to know if you could do this procedure by hand (die grinder and carbide tip) or do you need to use a boring machine for the fly cut?

Cheers Pat. I have split and empty 36Y cases on my bench.
I can see no reason why a steady hand and paitence couldn't achieve the required result when it is the only practical option.

I'll make a few phone calls to some engineering shops, I might be surprised.
Motorbike engines are not their thing and they usually refuse to work on them.
Granted, this should be pretty risk free.
All previous work like this was a simple case posting it to the UK, not an option anymore due to duties and taxes charged on both legs of the journey.

It's a nightmare.

Some metric figures for the openings required would be great.

Measure the cylinder sleeves with some calipers - and add a little.  This is not an interference fit - but you also don't want to remove a lot of excess material either.  I assume (but don't know for sure!) that a bit loose is better than a bit tight.

[Indiana jones]

I'll be using the base gasket as a guide.

[fj1289]

I agree use the base gasket if doing it by hand - thought you were looking for a dimension to pass to a machinist while trying to find a local shop.  

Here is how I just did mine:

Marked out the base gasket opening:


After grinding with 50 grit sanding drum.   Also followed up with 80 grit and 120 grit.


What I used: