1982 CB750F... The resto-not

The Jimbonaut

Active Member
Progress. Picked up all four colours of Plastigage from the local Napa as I had no idea which colour I needed. Turns out it's green. Flipped the upper case upside-down and onto a milk crate -



installed the new yellow bearing shells into the lower case -



cleaned the journals and then lowered the crank into the upper case -



cut the plastigage and placed a length across each main journal -



then lowered the lower case onto the upper, making sure not to move the crank while I was at it. Torqued the crankcase bolts in sequence to spec, then removed them, and then lifted the lower case back off and checked the plastigage -



0.051mm or 0.002". Right at the looser end of spec, which is what I was expecting/hoping to see given that the bearing shells I chose (the yellows) should be the loosest. Just to recap, I chose (was advised to use) yellows as I could no longer see the colour on the shells that needed replacing. 2 were showing copper so I decided to change all 5 lower case bearings.

Hoping that means I'm in the clear as far as clearances go on the main journals - tomorrow I'll check the crankpin and con rod clearances.
 

The Jimbonaut

Active Member
trek97 said:
Ha, yeah man - like most things that happen in my garage so far it'll be a first. Wanted to take my time with this and give myself the best shot of not fucking things up. That, and it took me ages to get my shit in gear and order the parts I needed. Still, all my ducks are in a neat little row now so time to quack.
 

The Jimbonaut

Active Member
Ok well things stalled. Started rebuilding the primary shaft last week (installed the new rubber dampers, installed the bearings etc) and then found out that I'd lost a tiny pin that anchors a washer to one of the split gears. I thought the pin was attached but turns out it wasn't - an hour of looking on the floor and a week later after ordering a new one from Honda and this turned up today -



Tiny, but crucial. You can see where it lives on the right had side of the gear -



Got it installed before i lost it again, and got the shaft rebuilt. Dropped it in the case, temporarily bolted upper and lower case together and then torqued the bolt in the primary shaft to spec. You need to wedge a broad screwdriver in between the teeth of the shaft and the case itself here -



in order to torque the thing.

Primary shaft done.
 

The Jimbonaut

Active Member
Having never completely rebuilt an engine before, my plan is to do so upside-down. The engine, not me. I remember how tricky it was to lower the cylinder down onto the piston and rings on my KLR, and that's a single cylinder thumper. And it probably wasn't even that hard - I just really made a meal of it. So, I'm pretty sure there's another method that involves installing the pistons - with the con rods already attached to them - into the cylinders, and then mate the con rods to the crank which is itself installed in the upside-down crankcase.

Anyone done this? Ultimately doable? Pitfalls I should know about? Or is this the way everyone does it and I'm just late to the party?
 

irk miller

You've been mostly-dead all day.
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That's essentially how you install pistons on a small block Chevy and most V8s, with the piston attached to the con rod and slid into the cylinder from the top. I've never found it overly difficult to slide the cylinders over the pistons, especially since the cylinders have a bevel that helps compress the rings as they go over. Assembly lube goes a long way toward helping ease the process. I don't have ring compressors either. Just my fingertips and the tip of a plastic spudger.
 

Maritime

Active Member
If the bottom end is open you can do it that way fine. when just refreshing the top end Irks method is how you have to do it. Either way good luck, take your time and you'll be fine.
 

irk miller

You've been mostly-dead all day.
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I challenge anyone to produce a service manual that says to install the pistons and such that way- top end rebuild only or not. It's not that hard to do by sliding the cylinders over the pistons. Just line them up at the same spot in the stroke, block underneath the skirt so they don't move, then start working the cylinders over. The pistons will be close enough in tolerance that they help keep things from getting too far out of line. You can slide it down to the top of the first ring, then push the ring in with a spudger and work around the perimeter. The bevel at the base of the sleeve will help this along. The weight of the cylinder will make the piston slide up into the bore. Then once all four of the first rings are in, you can tap the cylinder with a dead blow until they get to the middle rings. Just taps where the weight of the hammer is doing the work, not force from your arms. It's really not hard and because a 4 cylinder has much smaller pistons, you can't totally compare the experience with a bigger single piston. I don't see how playing a game of Twister with the case upside down is any better.
 

The Jimbonaut

Active Member
Duly noted Irk - I think I'll do this the standard, right-way-up way after all.

Like the new T00L album, this is a long time coming. Got the call from my man Gabe that my bolts were finally ready from the platers -



mmmmmm, shiny. So after a month hiatus the engine rebuild could proceed. After a couple of dry runs I found that the primary chain tensioner spring assembly kept dislocating and preventing the cases from closing properly. A zip tie took care of that - keeps the tensioner in the right place and the spring mechanism underneath it where it needs to be -



I also realized that the small split pin actually passes through a small hole in the tensioner dowel that I'd missed before -



Instead of putting the engine in first gear (as directed by both the FSM and Clymers) it had been suggested to put the transmission in neutral instead for easier assembly, so that's what I did. This is the position on the gear selector whatnot that indicates neutral -



Parked the bolts in the correct holes on the boards I'd made and applied molybdenum grease to all the threads -



Applied a thin layer of ThreeBond 1184 to the lower case (and a little to the areas on the upper case as indicated by the FSM) and spread it with a foam brush to ensure a light coat, avoiding getting the stuff anywhere near the crank bearings. With the zip tie holding the primary shaft tensioner, lowering the upper case onto the lower was no drama, and the gear forks engaged easily too in the neutral position. Torqued up the bolts and things are starting to look engine-like again -



God knows it's been a while. Hope to get the pistons installed later today, and get the cylinder block installed. As they say in India - good and better sir.
 

The Jimbonaut

Active Member
Question - gasket sealer on the base gasket? I used a light coat on the oil pan gasket, can't remember what the general opinion is on base gaskets though...
 

adventurco

Nick Ol' Eye
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Jimbonaut said:
Question - gasket sealer on the base gasket? I used a light coat on the oil pan gasket, can't remember what the general opinion is on base gaskets though...
I'll usually just wet em down with oil and install. I'll use a thin coat of sealant only if I know its something that leaked previously.
 

adventurco

Nick Ol' Eye
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Jimbonaut said:
Cool, cheers man - I've read that some people use a thin layer of bearing grease?
Depends. I've done it before it just makes a mess. Sometimes if its a cover that will be removed for maintenance I'll use hondabond on the cover side and oil/grease on the crankcase side so it sticks to the cover rather than the crankcase. All personal preference
 

The Jimbonaut

Active Member
Makes sense. Another question mate - piston ring gap. I bought an aftermarket set (cylinder is now overbored to 823) but the pistons and rings did not come with any info. Is there any difference between the two rings in terms of which one goes on top and which one goes below on the piston? Also, would the OEM gap specs also apply to these rings?
 

irk miller

You've been mostly-dead all day.
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Jimbonaut said:
Makes sense. Another question mate - piston ring gap. I bought an aftermarket set (cylinder is now overbored to 823) but the pistons and rings did not come with any info. Is there any difference between the two rings in terms of which one goes on top and which one goes below on the piston? Also, would the OEM gap specs also apply to these rings?
.004" ring gap per inch of bore on the compression ring and .005" for the second ring. That's a minimum ring gap, not maximum.
 

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