Main Bearing Shells proud of Crankcases

[royhall]

You could try  a "Does anyone live in Devon" post and see if anybody is near to you. A lot of members are willing to call round in person to have a look. It can be difficult to advise correctly on just a few forum photo's. Cheers Roy.

[Clem2112]

Simple check I would try.
Put new and old shells side by side, edges down, to see if they match for size and shape - are the new ones slightly out of round?, even if they are not perfectly circular they should be ok when clamped in between the casing halves.

[royhall]

Like I said in the earlier post, I dont think you have a problem with the shells standing proud as you have already had it together to get a Plastigauge reading so they must push down correctly. They have probably just sprung back out when you removed the crank. All you need is a solid opinion on the condition of the crank journals and your good to go. If somebody in the know lives near you being in front of the crank makes all the difference. You cant really get the feel and look from photo's. This is an example of crank polishing.  https://www.youtube.com/watch?v=mHVzyvszbhw  Its the first picture you posted (with the Plastigauge) that had me concerned. Our resident expert on these things is BryanJ. Give him a PM and see what he recommends. Cheers Roy.

[hairygit]

Simple check I would try.
Put new and old shells side by side, edges down, to see if they match for size and shape - are the new ones slightly out of round?, even if they are not perfectly circular they should be ok when clamped in between the casing halves.

  That's why I suggested putting the crankcase halves together, to see if it all drops into place! Chances are at some point since manufacture they have had had something on top of them that has caused them to open up a fraction, my guess would be something dumped on top of the package they were shipped to you in, bloody postal companies! But, provided they aren't creased (easy to spot!) they should be fine to use. I'm about half an hour from you (A little village 5 miles S.E. of Exeter) but due to health issues driving is out of the question at the moment, but if you're not in a desperate hurry I'm more than willing to hop on a bus or train and come have a look for you.

[simco1964]

Hi,
    If its any easier, I could pop up and see you? I drive though Woodbury on the way to Budleigh Salterton (walking), would be better on the bike !! Have emailed BryanJ on RoyHall's recommendation to see what he thinks?
    Going to reassemble crankcases with crank in situ and check if casings are flush with each other then hopefully i'll know that its just the springing out the casings abit.
     But what i also need to know is if I can use the next shell size up to reduce the amount of clearance?

Simon

[hairygit]

I wouldn't advise it, as the plastigauge gave the right sizes, little point increasing clearances, just reduces the oil pressure at the mains and big ends, as the oil can squeeze past them more easily. 

[simco1964]

Hi,
   Please tell me if my assumption is wrong!! but why cant you put the next coloured shell up? ie go from yellow to green? would that not reduce the clearance?

[hairygit]

You could, but you would need to run it in VERY gently and carefully, really only recommended if the correct shells are not available. Motorcycle engines are built to much tighter tolerances than car engines, and when running in new shells, using the revs is not the issue, it's making sure you use the gearbox sensibly, not allowing the engine to "labour" during the running in period, as that would start scraping the surface of the shell, which you really don't want! After all, the film of oil under pressure is all that separates the crank from the shells, and imagine an engine rotating at 9-10,000 rpm, a split second of low oil pressure can cause catastrophic wear and damage. Mr Honda's engineers done a lot of research and development to decide the optimum clearances for parts, and why risk going against their advice? There are many high mileage 40+ yr old Hondas out there, many still on the original bottom ends, which says it all really. Get the clearances right, change oil and filter regularly, and they just keep on going!

[simco1964]

Cheers, as you have mentioned in previous messages, bigger the clearance lower the oil pressure, thats why I'm concerned regarding Main Bearing clearances, 4 off 0,063 and 1 off 0,076 which basically is max limit on clearances.
     So was hoping by using the next size shell up, it would hopefully bring clearances more in to tolerance, am I right in thinking this way?

[hairygit]

Yes indeed, but make sure whatever you do not to go below Honda's recommended clearances!

[Trigger]

Simple check I would try.
Put new and old shells side by side, edges down, to see if they match for size and shape - are the new ones slightly out of round?, even if they are not perfectly circular they should be ok when clamped in between the casing halves.

  That's why I suggested putting the crankcase halves together, to see if it all drops into place! Chances are at some point since manufacture they have had had something on top of them that has caused them to open up a fraction, my guess would be something dumped on top of the package they were shipped to you in, bloody postal companies! But, provided they aren't creased (easy to spot!) they should be fine to use. I'm about half an hour from you (A little village 5 miles S.E. of Exeter) but due to health issues driving is out of the question at the moment, but if you're not in a desperate hurry I'm more than willing to hop on a bus or train and come have a look for you.

If I pay the bus fare, will you come and give me a hand for a couple of days 

[hairygit]

As long as it doesn't involve heavy lifting, 3 hernias are more than enough thanks!

[Bryanj]

just reading a very early 750 manual and it states " when the bearing is mounted into the crankcase, the top of the bearing should be extended above the case  mounting flange by 0.0027~0.0039 in (0.068~0.098 mm) so you sound about right

[simco1964]

Cheers Bryan, Feel alot happier now you've mentioned that!!!