Cylinders/head are off for rebuild. Primary chaincase is off. Should I pull Crankcase and rebuild it? Mission Creep!!

This is the final wisdom I ask the forum for !

My new used Cylinders are now bored to plus 20 thou with new pistons and new valves and guides are on the way.
There was so much wear in the plus 40 thou cylinders that trying plus 60 thou may not have worked.

I lapped in the oil pump a year ago and have about 45psi cold and between 8 and 12 psi warm, depending on how hot a day it is outside.

With the Primary Chaincase off, should I pull the crankcase out and put in new main bearings and then replace the conrod bearings (and pastigauge check the clearance)?
If I were to do that, what else should I do (like camshaft bearings?)?

There is another thread whereby Stephen has a smoking left cylinder and is considering what to do. My project may be a classic example of
mission creep should Stephen decide to open up his engine!!

Many thanks to all for your great support on this mission....!

Dennis

When was the sludge trap last cleaned?

DennisMo said:

This is the final wisdom I ask the forum for !

My new used Cylinders are now bored to plus 20 thou with new pistons and new valves and guides are on the way.
There was so much wear in the plus 40 thou cylinders that trying plus 60 thou may not have worked.

I lapped in the oil pump a year ago and have about 45psi cold and between 8 and 12 psi warm, depending on how hot a day it is outside.

With the Primary Chaincase off, should I pull the crankcase out and put in new main bearings and then replace the conrod bearings (and pastigauge check the clearance)?
If I were to do that, what else should I do (like camshaft bearings?)?

There is another thread whereby Stephen has a smoking left cylinder and is considering what to do. My project may be a classic example of
mission creep should Stephen decide to open up his engine!!

Many thanks to all for your great support on this mission....!

Dennis

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I do every time. But, I'm rebuilding engines and bikes for people and building bikes to sell.

I don't know the costs to Canada, to the US, you'll need two 06-4118 which cost around $120 delivered each from AN. The shell set is around $130 delivered from AN but call/write me. You need 4 conrod nuts ( 06-7827) and the crankshaft stud nut set (06-7094) which is around $80 delivered from AN if you're going to split the crank - I always do even though most of the time if the bike has an oil filter, it's doesn't appear to the needed.

I've forgotten your engine/year.

I do more Combats that anything else. I always change the timing side camshaft bushing on those and 73 750s to the MK3 style bushings. This is somewhere between easy and pull your hair out! A proper reamer and re-size ball helps but getting it perfectly aligned with the drive side can be a PITA.

Most 72/73 crankshafts I've split have 1-4 machining errors in the timing side journal. Clearly, the engines run with them. The most common error is that when drilling the oil hole they stopped short of letting the bit go well into the void and they did not look inside. Many (most) on at least one of the hole has a hanging piece of metal due to that and often when they don't I find that piece of metal in the crank. It's that way on both holes sometimes. Also, often the drive side oil holes will be slightly countersunk and the timing side one or both won't be countersunk and you can see a line in the shell. I lightly countersink before polishing.

Sometimes I find these things on earlier or later crankshafts, but not usually.

So are you a worry wart? If so, get to it. Is it worth the money to you? If so, you will increase your knowledge so why not. If the bike has an oil filter and gave you no reason to worry about the bottom end - than maybe leave well enough alone.

Stripping and rebuilding the top half is the hardest bit, the bottom end is just a few big lumps.
I bet you would be really peed of if you didn't do the bottom end then heard a grumbling main or a ticking big end

If the engine already has 'Superblend' main in then you are only concerned with the big ends. If the oil pressure stays the same then leave be, if it starts dropping then relap the oil pump and if it goes back to the current levels again leave be.

I'm with Greg - the level of effort doing a complete engine refresh vs trying to piecemeal address whatever ongoing smoking/performance issues isn't that much greater, and the knowledge that there's a blueprinted engine in the bike just has to be worth it.
Although I've upgraded a few engines to superblends, I've never needed to replace any yet.

it's really not too much more work to strip and rebuild the bottom, unless you find something out of the ordinary, and give you the chance to do other stuff like relocate the TS drain etc

Previous owner said he had cleaned out crank sludge. It is a 1973 engine with oil filter.

That is good .
So how are the cam lobes ?

I will inspect cam lobes with a flashlight!!

What about the conrod bearings, i be more worried about the wear on those slipper bearings than the main bearings.
Why do 1/2 a job if you have no idea of what been done, for my own mind and long term ownership i be doing the botton end as well, never trust what the old owner might say, and if things are good it be a bit off your own mine, better to be safe than sorry later down the road.

Ashley

ashman said:

What about the conrod bearings, i be more worried about the wear on those slipper bearings than the main bearings.
Why do 1/2 a job if you have no idea of what been done, for my own mind and long term ownership i be doing the botton end as well, never trust what the old owner might say, and if things are good it be a bit off your own mine, better to be safe than sorry later down the road.

Ashley

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