1982 CB750F...Better Devil

adventurco

Nick Ol' Eye
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Jimbonaut said:
Yeah, I think that's it. Need to dial down the drill. Even with the fine grit stones I'm guessing the honing tool removes material from the inside of the sleeve, and so overdoing it is a no-no?
Yep. You basically want to go the least amount possible to get a good 45 degree cross hatch.
 

cxman

Active Member
DTT SUPPORTER
get a ball hone or some call them flex hones

with the 3 jaw hones you will bell mouth the cylinder before you get nice crosshatch

a well lubed ball hone you are done in a minute less than 1/2 thou removed

and the cylinder is degalzed and cross hatched
 

Jimbonaut

Well-Known Member
DTT SUPPORTER
Worked on the brake calipers yesterday, man they're crusty. Thankfully I now have a small air compressor in the garage so getting the pistons out wasn't too much trouble, but one did need some encouragement from some pliers to get it past the roached seals. The piston is slightly scratched and I'm pretty sure I can clean it up with some fine grit sandpaper and some Autosol metal polish. Is that cool? I'll be careful no to remove any material from the piston - just the scratch.

The seal grooves inside each caliper are in pretty rough shape too, and the seals were all completely destroyed (whoever rode this beast last must have had zero heel left on their boots - I think that must've been the only way they got this thing to slow down). I used mechanic's picks to remove all the crud in there, and will let them sit in some clean brake fluid for a while too. Is there anything else I can/should do to get these thing clean before rebuilding them?

The rear brake master cylinder however was in the worst shape. The thing just looks awful - all the seals are toast and it's covered in crystallized brake fluid. Once I got the boot off to dig out the circlip, it looked full of rust and the circlip ain't budging for love or money - in fact it shattered my circlip pliers trying to remove it. Any ideas on how I can get that thing out? Tried soaking it in PB Blaster to - so far - no avail.
 

cxman

Active Member
DTT SUPPORTER
boil it in water that covers the master cylinder with 2oz of lemon juice that will loosen most of it up

boil for 10- 15 minutes then try removing the ring while its hot
 

stroker crazy

crazy as a fox
A slow but sure method to remove rust without damaging good metal is to soak it in a mix of one part molasses to eight parts water.
Animal feed molasses is marginally better than that meant for human consumption.
Remove part from the mix every now and then to brush off dissolved rust.

An oldie but a goldie!
(specially on sheet metal when you can't afford make it any thinner)

Crazy
 

CarbsAndCylinders

Careful With That Axe Eugene
Would either of these products work, without damaging the aluminum?

https://www.canadiantire.ca/en/pdp/metal-rescue-rust-remover-bath-3-78-l-0477920p.0477920.html?gclid=Cj0KCQjwg73kBRDVARIsAF-kEH9MFJkUa1bubZN41y5wIdyEow9vCYGz2duyCiqfnT9O1EUVjDtlGJoaAjz1EALw_wcB&gclsrc=aw.ds#store=606

https://www.uline.ca/Product/Detail/S-18420/Cleaning-Supplies/CLR-Calcium-Lime-and-Rust-Remover-828-mL-Bottle?pricode=YE390&gadtype=pla&id=S-18420&gclid=Cj0KCQjwg73kBRDVARIsAF-kEH9MLxFTryfW6qdTE_VMp7bemlSKiV-NnNJbdFuvv__d4Km-oGPBzrMaAhq2EALw_wcB&gclsrc=aw.ds
 

adventurco

Nick Ol' Eye
DTT BOTM WINNER
Vinegar?

You'll probably have to break that circlip to get it out. They are a PITA to reach with snap ring pliers and even if you can get to them they never want to come out. The last MC I rebuilt I broke the circlip into pieces and pulled out the chunks. Replacing it is easy as you can use the snap ring pliers to get it to fit in the bore, and then use a socket thats close to the same diameter as the bore to push it down evenly until it seats.
 

Jimbonaut

Well-Known Member
DTT SUPPORTER
Thanks guys - I ended up leaving the thing soaking in PB Blaster overnight and then attacking the circlip with a couple of mechanics picks. Wrestled that thing out, then had to manhandle the piston and its washer. Man what a mess. Still, got it all out and hopefully the master cylinder itself will be salvageable. The bores cleaned up ok -




Good to learn about those rust-shifting techniques. I've used Metal Rescue before on a rusty gas tank - that stuff is the business. Has one job to do, and does it brilliantly.
 

Jimbonaut

Well-Known Member
DTT SUPPORTER
Uncovered a bit of a mystery too yesterday. After measuring the cylinder bores it looked like all of them were out of spec, and larger than the wear limit specified in the Clymers manual. Although my first reaction was to get the hump knowing I was going to have to shell out on an overbore and new pistons, I then thought to check the piston diameter. I hadn't removed the pistons from the con rods so that was the first job (no circlips took a dive into the crankcase, but boy did they try) - no drama.

Then measured them. Here's the table showing the piston diameter, and the corresponding bore diameter -



All the ring gaps were within spec (at least they were when referencing the stock ring gap specs in Clymers). Could it be that the cylinders have already been bored and new, larger pistons installed? I mean, I can't think of any other scenario really. I don't know how stock pistons are marked, but the ones in my engine are marked "25" (albeit faintly) on the top -



and "425 8" on the side -



I know they're OEM as they're marked Honda on the other side -



Any ideas?
 

adventurco

Nick Ol' Eye
DTT BOTM WINNER
I'd think that the "25" on the crown could possibly mean .25mm overbore which is first over. Can you check your measurements with the manual and compare? If you add .25 to the specs in the manual do the numbers make more sense? There should also be a piston to cylinder clearance value that should hold true even in the case of an overbore.
 

Maritime

Well-Known Member
You're consistant with .003 on each piston for clearance so they very well could be overbore pistons and the machine shop matches the bore to each piston when they do it. the ring gap is the ring gap no matter the piston size, the ring Diameter however would be larger than stock so see if you can find the 1 over sizes and that may be what you have already. It would make sense that you got good ring gap measurements on the rings if this was a recent overbore.
 

Jimbonaut

Well-Known Member
DTT SUPPORTER
Thanks fellas - I've dug up what I can on the internet and it looks like the "25" marking on the top of the piston may well be the indicator that a .25mm overbore has been performed on the engine. Haven't found anything conclusive yet, but things are pointing in that direction.

I'll check out the specs again and re-jig the numbers allowing for the extra .25mm. Hopefully all will point to these being over-size. The compression on the engine was excellent (165psi across all cylinders) so I guess this could be part of the reason - the thing is I'm just not experienced enough to know (or look out for) the tells that the engine has been opened up and worked on.
 

doc_rot

Oh the usual... I bowl, I drive around...
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the easiest tell-tale sign that an engine has been opened up is the gasket surfaces have already been scraped. I would run those pistons with zero worry, however new rings may not be a bad idea as you can see that carbon has been getting past the first ring. Not the end of the world, but not ideal either. And definitely get new circlips.
 

Jimbonaut

Well-Known Member
DTT SUPPORTER
Cheers Doc, gotta say that's a huge comfort. If you'd run these pistons with zero worry that's more than enough for me. I'll look into a new set of rings - when you say circlips are you talking about the circlips on the wrist pins? Why would they need to be replaced? Metal fatigue?
 

doc_rot

Oh the usual... I bowl, I drive around...
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DTT BOTM WINNER
Jimbonaut said:
Cheers Doc, gotta say that's a huge comfort. If you'd run these pistons with zero worry that's more than enough for me. I'll look into a new set of rings - when you say circlips are you talking about the circlips on the wrist pins? Why would they need to be replaced? Metal fatigue?
yeah the wrist pin circlips. getting them out can cause them to loose spring tension. its not something you want to pop out while the engine is running. Its cheap insurance.
 

Jimbonaut

Well-Known Member
DTT SUPPORTER
Was having a late night look at some photos of the head and cylinder block (before I honed them) and noticed something I'd missed before. There's what looks like an 'overspill' pattern of carbon that is exactly the same on the top of each cylinder -



close up -



What would cause that? Knowing now that the cylinders have - at some point, not very recently judging by what little info I got from the PO when I bought the bike - been overbored and the pistons switched out with .25mm larger ones, would this have happened after the piston switch? I'm assuming yes of course, in which case what would have caused it? Poorly fitted gasket? Poorly honed mating surfaces? Is it normal perhaps? Very interested to learn more about this.
 

adventurco

Nick Ol' Eye
DTT BOTM WINNER
Looks like it could be just an abnormally shaped aftermarket head gasket. Since there is no blowby it wouldn't be caused by a leaky head gasket or bad mating surfaces.
 

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