Topic: Cooked my case...

[bustedknuckles]

The bike is completely torn down, case split, so I decided to pretty it up before reassembly.  High temp primer and paint for the case, but the primer called for a curing process.
30 min @ 250* Cool for 30
30 min @ 400* Cool for 30
30 min @600*

I removed everything from the cases, with the exception of the main bearings, which I forgot to pull.  Things went well until my wife got home and found me cooking an engine case in the house.  However, on inspection today, I see tiny balls of metal that look like solder drops in the areas of the main bearings.  Did I manage to melt off some softer coating on the bearings?  I'm not going to take the chance, so I'll just end up replacing them, but this seems pretty odd.  Max temp was 550 since my oven doesn't go to 600.

[flybox1]

The bike is completely torn down, case split, so I decided to pretty it up before reassembly.  High temp primer and paint for the case, but the primer called for a curing process.
30 min @ 250* Cool for 30
30 min @ 400* Cool for 30
30 min @600*

I removed everything from the cases, with the exception of the main bearings, which I forgot to pull.  Things went well until my wife got home and found me cooking an engine case in the house.  However, on inspection today, I see tiny balls of metal that look like solder drops in the areas of the main bearings.  Did I manage to melt off some softer coating on the bearings?  I'm not going to take the chance, so I'll just end up replacing them, but this seems pretty odd.  Max temp was 550 since my oven doesn't go to 600.

anything over 400* is a bit excessive....
if you prepped your cases properly, 250-300 for 30 min is all you really need
your cases should be emptied of all other parts before curing the paint

[754]

I don't even like the thought of curing powder at 400 on a lot of parts... I would not run the cases that hot.

[bustedknuckles]

It seemed hot to me, but 30 minutes with an empty case seemed doable and there was a little bit of "if the instructions say so" laziness.  I know better, but went with what the can said.   I figured if all of the other components were out, it wouldn't hurt, so long as temperature changes were gradual. 

The bearings being left in were an oversight, a result of getting a little too excited to get this thing back together.  I'll definitely replace them, but I'm just surprised that there was some metallic compound in there that melted at 550.  I wish I could get a decent picture, but I can't get in that close.  It looks almost like welding spatter.  Tiny little shiny spheres.  It'll all get cleaned up and new bearings will go in. 

[flybox1]

What is considered 'good' on the back of a modern can doesn't always translate to what is 'good' to do to our 35+ year old bikes.  If you are ever unsure of what is 'good',  ask!  Highly likely its been documented here....

Will a magnet pick up the balls?

[bustedknuckles]

As I get older, I get better at doing things right.  Some days, I don't feel so old... 

The melted stuff is non-magnetic.  I'm guessing it must be some kind of coating that melted off.  There aren't too many metals that melt at 550 or below, so I'm a little baffled. 
http://www.engineeringtoolbox.com/melting-temperature-metals-d_860.html

Hopefully I haven't weakened the case by cooking it.  I suppose it's possible that I've annealed it, but I think you have to be up around 700 or 800 to anneal aluminum. 

Unfortunately, a new case isn't in the budget so it'll be a mystery until it isn't...

The other fun part is that I cooked the bearings before I checked to see what color they were.  Now I can't tell.  Time to slow down...

[HondaMan]

The plain bearings are a babbet type, which are quite soft. They resemble a high-temp version of Cerrobend metals. To make them, they are heated up to 700 degrees to melt, then formed and cooled to 400 degrees, then pressed to final depth (thickness). The surface coating (that dull finish) was sprayed on to the ones I watched being made at Caterpillar, circa 1969.

[bustedknuckles]

HondaMan, looks like I've de-babbitted them...  That handy chart I linked to lists babbitt at 480*.  Oh well, I should replace them anyway.  Off to get some plastigauge.  How much of an effect will the lack of coating have on any measurements?  Maybe I'll just order some greens, check them with the plastiguage, and hope they're right.

[Whaleman]

I would be worried about the o-ring in the big round plate in the bottom case. The o-ring does not show as a part on Honda finch. The big plate just knocks out from the inside and is sealed with a big o-ring. I replaced mine about 14 years ago with a o-ring I got from a supply house. Dan

[bustedknuckles]

Whaleman, thanks for that info!  I'll check on that.  I'm sure I missed it.  That would have been a nasty surprise.

Also thanks to HondaMan for the bearing info. 

[HondaMan]

That coating is a sort of Parkerizing that helps burnish in the new bearings. If yours are already broken-in, I seriously doubt any trouble would come of it. New bearings are always nice, though: the engines run real smooth with them.

[bustedknuckles]

Hondaman, good to know!  I'm going to plastiguage and see what I get.  Doing a rebuild right, while still being on a budget is tough.  What looks like a couple hundred bucks quickly grows as you get into it, especially for headstrong whippersnappers....

[HondaMan]

Yeah, a full DIY rebuild ends up around $900-$1500 in parts and services, it seems. I've been able to get up to where I can do 80% of the valve jobs myself, but there are still some that I have to hand off for the $300 shop treatment. The bore jobs are still theirs too, until I can buy a nice boring bar again. Had one long ago, but someone else has it now. 

[bustedknuckles]

I did a little research on babbitt metal (if you can call wikipedia research) and this is pretty interesting:  http://en.wikipedia.org/wiki/Babbitt_(metal)

Basically, it says that the babbitt alloy consists of soft metal with harder crystals.  The soft metal wears and allows for the passage of oil between the harder bits. 

That would indicate that the babbitt, rather than being a protective coating, is an essential part of the lubrication process.  So I'm definitely putting in new bearings.  It's kind of a no-brainer, but I'm a cheap/poor bastard that likes to take shortcuts (I'm trying to be better!) and it's nice to know some of the science behind it. 

And Hondaman, I know you're absolutely right about the cost of a rebuild.  I wish I had the dough to do it right, but it's going to be new seals, bearings, rings, and all the little replaceable stuff, then put it back together.  I'm skipping the machine work.  I'd love to put in new valves, but they're almost impossible to find for the K8, so they're getting lapped and polished.   I'm thinking I'll get it all back together for around $500 in parts.  Considering that's what I paid for the bike, a $1000 ride is okay with me.