Plastigage? and main bearings.

[SumpMagnet]

How exactly does this stuff work?

Was going to reuse the shells on my 750 project until...today. 

Got some time off work so I decided to start cleaning down the crankcases to get them ready for paint. Stripped off the wrappings they were hibernating in...only to see an issue. Where the main bearing shells used to be showing that even dull wear ..I saw one of them had a 'shiny' mark on it. Shiny isn't good. Even worse is when you find the shiny mark is a gouge. It's not wear...something pointed has fallen on the bearing, and dug a chunk out. It;s sharp and stickes up above the worn surface.

That tells me it's scrap.

If I am going to have to replace one....I am assuming I should be replacing the whole lot as a set?

I think I need plastigage to check clearance.... but I have never done anything like this on a plain bearing engine. Don;t have a clue where to start!

[taysidedragon]

Buy the Plastiguage that covers the range of bearing clearances that you're looking for. I bought a mixed pack that had Red and Green colours for my 400f.
You lay a short strip across one bearing shell for each pair then place the crank back in and bolt the two crankcase halfs together to the correct torque.  Then separate the two halves and remove the crank.

The Plastiguage squashes flat and takes up the exact thickness of the clearance gap. The smaller the clearance the more it squashes and the wider the Plastiguage goes. The set includes a strip of card showing the different widths for measuring your clearance gap. Just find the closest one to your result.

[SumpMagnet]

Do I bolt it up dry....or with Hondabond sealant in place?

Better go read up the manual for proper clearance.

[Oddjob]

I have a single 750 shell you can have for free but I have no idea what it is, could be a main or a big end, could be green or brown etc.

What do you need?

[taysidedragon]

Do I bolt it up dry....or with Hondabond sealant in place?

Better go read up the manual for proper clearance.

Dry, you're taking it apart again straight away.

[SumpMagnet]

@oddjob Big ends feel solid and smooth. Main shells show wear but were usable IMHO ...until I found the damaged one. I will need to find out what I have, and what I need.

Don't know what I have.,..so I guess thats the next step. Plus ordering some plastigage.

Thanks @taysidedragon ..appreciate the advice. I wasn;t sure if you had to allow clearance for sealant. Never had to do this before, as previous bottom end rebuilds had always been roller bearing cranks. Either Suzuki 4's or 2 strokes where you send the crank off to be split and rebuilt with new seals and bearings....and just drop it in. Only other plain bearing setups I have met have been top-end...with no shells. So this is a step into the unknown.

I also need to look at a few of the gearbox bearings, as it looks like a few had been moving. Might need a few drops of bearing fit when I rebuild.

[McCabe-Thiele (Ted)]

[ Guests cannot view attachments ] Be careful when buying Plastigauge by colour you really need to buy by the clearance size range as some cheaper brands sell green but it's the wrong range.

My Green Flexigauge is 0.025 mm to 0.076 mm / or 0.001" to 0.003 "

Attached document was sent to me by a member.

[K2-K6]

"I wasn;t sure if you had to allow clearance for sealant."

It seems odd, but all of the sealant is effectively squeezed out during tightening of the bolts to make it metal to metal joint whether sealant is used or not. Obviously pointless to waste sealant and clean surfaces again during test assembly, as already pointed out above.

The crankcase is bored during manufacturing to make the holes as perfect as possible without any sealant ordinarily.  Really what's left when assembly is complete is just a small amount sitting in any imperfect parts of the joint to prevent oil leaking during use and shouldn't change the tolerances at all.

[Oddjob]

Check the edge of the bearing and see if any of the colour marking is still visible.

Pretty sure mine is a main as it came with some 500 main shells from the states. I'm 70% sure it's a green.

[SumpMagnet]

I'll go investigate further and see if I can see any colour or clue.

But thanks for the input! It's really helping me get my head around this

[Oddjob]

Check all the bearings for colours, if removing put them back in exactly the same place. I don't normally advise this BUT if one of the bearings still has a remnant of the colour on it check the back of the shell for production codes. As they would have been fitted in the factory from a bin of shells they'd all be the same code, if you can find a shell with say green on it and it's marked say D7E-S and your mystery shell is also marked D7E-S then your mystery shell would also be a green. Generally production marks are useless but in your case they might just be a life saver. 

[SumpMagnet]

Could see some faint colour on the shells on 3 of the upper. Lower ones were harder to spot. Popped out the best of the uppers ...and:





I am assuming this is the right sort of colour, and it is definitely green. Got code D7H stamped on the back. So, I assume I need to get a set of green shells and I should be good?
Or do I buy plastigage, check clearance, and try and work out the correct size from there?

[Oddjob]

Yep, that's a green. You could just buy 1 shell, ideally you'd buy 2 but TBH you really only do that because you're replacing both due to wear, you're not, it's due to damage and you could just replace the one.

I just found my odd 750 shell and it's a brown conrod shell.

[SumpMagnet]

brilliant

I think the best approach will be to Plastigage it for peace of mind, as that will also confirm the others are not worn. There is no scoring or obvious damage....but it should give me the clearances.
But to pick up the one shell I need assuming everything else comes out sweet.

I assume the crank itself doesn;t really wear to any appreciable amount and the softer shells are where the wear happens. As long as the oil flows like it should anyway!
So Honda slap it together with shells that give the correct clearance, as long as I stick to the same ones Honda used...the clearance should come out right.

They are also in stock at Silvers....so I'd better get a shopping list together to avoid paying silly postage for one tiny thing

[Oddjob]

The problem with plastigauge is that whilst it does show if there is wear it can't tell you what is worn, is it the crank?, is it the shell?. The only way to get a definitive answer is to use plastigauge with new shells. That way you see what the clearance is and can calculate what colour shell you need (if any) to get back within spec. However if you use plastigauge with old shells and they still show the clearance within spec then at least your mind is at rest.

As for the journal with the damaged shell. See if you can find another green in any of the other journals, temporarily replace the damaged one with another green from another journal, measure the clearance, if still in spec then you're good to go with buying just one shell. If none of the other journals show colour on the shells then find one with the same production markings as it's bound to be another green, same bin, same batch, same colour etc