Topic: 1973 CB350F "Modest Original" build

[iiAtlas]

Yes, yes and yes. Facing forward, leftmost is 1-4 while seated. Keep rings in place during soak, then measure end gap in place on piston, then again after removal. While on piston in not very accurate, but I use it as a relative expansion metric.

Here's another new entrant to the unibox with stacks: http://cognitomoto.com/collections/new-products/products/cb550-air-intake-box Though not yet available for your motor.

I saw the Cognito offering, but in addition to not being available to our bikes they are also a good $75 more expensive    iiAtlas, that thread you found has some good baseline tuning information (albeit for a much larger engine).  Good to know about blocking off the top of the filter.

Yes!  A good writeup for a not-oft-mentioned style airbox.  I know it will take some tweaking but I'm confident I'll be able to get this little girl running right with the Steel Dragon "unibox".

[iiAtlas]

All -

Found this on the engine and thought it was worth noting.  There is a very strange "gap" here between the two and three cylinder intakes.



It looks almost like a cutout.  I shined a light in and could not see it come out anywhere in the cylinders, so I don't think its a crack.  Is this a casting mark?







Just thought I'd share, was surprised when I saw it.

[grcamna2]

I believe those are casting 'cutouts'(if that's the correct word.. )which serve as kind of drains for when water gets on top of your cylinder head.. I think

[sbeckman7]

Yep mine has them too, nothing to worry about 

[iiAtlas]

Yep mine has them too, nothing to worry about 

I believe those are casting 'cutouts'(if that's the correct word.. )which serve as kind of drains for when water gets on top of your cylinder head.. I think

Phew!


Piston work tonight.  First, pictures of the sides as you all requested.  This is pre-cleaning attempt.

1(a)


1(b)


2(a)


2(b)


3(a)


3(b)


4(a)


4(b)


As you can see, the most notable signs of blow by are on pistons 2 (side b) and 3 (side b).  To my eye, the walls looks relatively good.  Next up I decided to start trying to remove some of that gunk off the piston heads.  I did a 20 minute soak in the chem-dip and then went at it with a disk similar to the one below.



1


2


3


4


They certainly are shinier than they were...someone with more knowledge will need to tell me if I a) ruined these, or b) did an okay job.  Either are totally possible.  I decided removing the gunk HAD to be better than leaving it on there.  Did I go too far?  Did I ruin these four pistons?  I wasn't able to get at the right angle to remove the gunk in the valve clearance cut outs on the piston.  With a Dremel I should be able too but didn't want to go much further than I already have.

One thing I did ruin, the rings on #2


I attempted to measure them but I think I may have done a horrible job.  I took my feeler guages and went around the top of each ring seeing which would fit in.  Factory said .006".  For the most part this was true.  Sometimes only a .004" would fit.  On one or two occasions I was able to fit .008".  Is the factory spec of .006 a max or does it hold true both ways?  Is being able to fit only a .004 in some locations a bad thing?  I also may have been wielding the tool incorrectly.  I will have to redo all of these measurements, but thought I'd share to gather some more info.

[sbeckman7]

Hmm I hope you didn't remove too much material from the tops!  At least they look clean

[iiAtlas]

Hmm I hope you didn't remove too much material from the tops!  At least they look clean

I do too..."At least they look clean " was my attitude at the time.  I'm ready to be schooled by the much more educated members here on the forums...bracing for impact...

[grcamna2]

I use a small,sharp flat blade screwdriver on the tops of the pistons and spend a good amount of time carefully scraping away at the carbon but try not to remove any metal as that will lower your compression ratio or alter the efficiency of your squish area which can affect how the engine builds power.The 'long,slow' process of cleaning them works Best. 
I recommend carefully scraping off the heavy stuff next time and then soaking them in some strong carb. cleaner to soften the stuff up so you can easily scrape away the last bit of it w/ a very dull safety razor(my preferred way..)and just keep away from doing any scraping on the lower/bottom piston skirts.I've also used #0000 steel wool very lightly on those lower skirts to gently smooth them w/o removing metal. That's the 'challenge'  when cleaning pistons.

[iiAtlas]

I use a small,sharp flat blade screwdriver on the tops of the pistons and spend a good amount of time carefully scraping away at the carbon but try not to remove any metal as that will lower your compression ratio or alter the efficiency of your squish area which can affect how the engine builds power.The 'long,slow' process of cleaning them works Best. 
I recommend carefully scraping off the heavy stuff next time and then soaking them in some strong carb. cleaner to soften the stuff up so you can easily scrape away the last bit of it w/ a very dull safety razor(my preferred way..)and just keep away from doing any scraping on the lower/bottom piston skirts.I've also used #0000 steel wool very lightly on those lower skirts to gently smooth them w/o removing metal. That's the 'challenge'  when cleaning pistons.

D'oh. This was my most heavy handed approach thus far. I think it was because I didn't really know what was under there or what to expect!  Live and learn. I'll be more careful with the valves. I don't think I took away much metal but of course who knows. What should be my next steps for cleaning these Pistons? Should I attempt to polish put the scratches?  Thanks for the input grcamna.

[grcamna2]

iiAtlas,
I'd just carefully finish scraping/cleaning the rest off the domes on them until you can see the same aluminum on all 4 of them and then compare how the shapes of the domes look between them.. hopefully you can sort of shape/clean/polish the domes on all 4 pistons(make sure you remember which # cylinders they orig. came from along w/ the ringsets) until they all match the one that has the most metal removed from that dome.I don't think you've done that much harm.When you run it for a while the carbon will fill those areas back up anyway.

[iiAtlas]

iiAtlas,
I'd just carefully finish scraping/cleaning the rest off the domes on them until you can see the same aluminum on all 4 of them and then compare how the shapes of the domes look between them.. hopefully you can sort of shape/clean/polish the domes on all 4 pistons(make sure you remember which # cylinders they orig. came from along w/ the ringsets) until they all match the one that has the most metal removed from that dome.I don't think you've done that much harm.When you run it for a while the carbon will fill those areas back up anyway.

Thanks, slow and steady this time.  I've got a long night ahead of me...appreciate the help.

[grcamna2]

The other areas to be very careful with are the ring 'lands'/grooves in the pistons.I would soak the pistons and rings in strong carb. cleaner for a good wile to soften up all the carbon in the ring grooves and on the rings.I use an old piston ring to clean out those ring grooves very slowly and carefully.I take an old piston ring and break it in half then use a bench grinder and slowly grind the broken end until it is fully squared and still sharp on the tip(but not on the flat sides,you don't want to remove Any metal from inside those piston ring grooves)and use that old piston ring to slowly remove carbon until you see an even band of aluminum.Soaking the piston in strong aluminum cleaner/carb.cleaner/solvent really makes short work out of this task. 
Did you have your cylinders and pistons checked for proper clearance yet(sorry haven't been following all the way through your thread)so you're sure everything is 'tight' to spec. on the fit ?

[iiAtlas]

The other areas to be very careful with are the ring 'lands'/grooves in the pistons.I would soak the pistons and rings in strong carb. cleaner for a good wile to soften up all the carbon in the ring grooves and on the rings.I use an old piston ring to clean out those ring grooves very slowly and carefully.I take an old piston ring and break it in half then use a bench grinder and slowly grind the broken end until it is fully squared and still sharp on the tip(but not on the flat sides,you don't want to remove Any metal from inside those piston ring grooves)and use that old piston ring to slowly remove carbon until you see an even band of aluminum.Soaking the piston in strong aluminum cleaner/carb.cleaner/solvent really makes short work out of this task. 
Did you have your cylinders and pistons checked for proper clearance yet(sorry haven't been following all the way through your thread)so you're sure everything is 'tight' to spec. on the fit ?

I knew the walls and piston ring areas were sensitive so I made sure to keep clear of them, thankfully.  I've just broken the ring on #2 so that can be the one I sharpen I'll do another batch of soaking in the Chem-dip that seemed to help loosen.

I have yet to measure the clearance while in the cylinder. I suppose I should do that before going much further.

[grcamna2]

Do you have an inside(I have calipers but that isn't enough to go down inside) micrometer? it might be best to take the cylinders to a machine shop that cares to measure the pistons/cylinders after you've cleaned them.

[iiAtlas]

Do you have an inside(I have calipers but that isn't enough to go down inside) micrometer? it might be best to take the cylinders to a machine shop that cares to measure the pistons/cylinders after you've cleaned them.

Have a set of exterior mics but no interior. Will order some off eBay. Tough to find an able and willing machine shop here in NYC :/ all the more reason I try to do this work myself.

I've scrapped the piston heads to the point I'd consider them "done" now. Wouldn't want to remove any more material. I'd like to give the ring groove cleaning a try but I'm worried about removing material.

[grcamna2]

Soak those 4 pistons in a strong solution for the recommended time and those carbon deposits will come right off w/ that piece of broken piston ring and a light scraping motion,it won't hurt them.

[sbeckman7]

For what it's worth, I had tremendous success de-gunking my V12 pistons with a standard utility razor (the kind that are sold in packs)

Before the razor, rag, and brake cleaner:


And after

[grcamna2]

Nice  That's quite a dished piston;what type of high performance engine is that,a Jag ?

[sbeckman7]

Nice  That's quite a dished piston;what type of high performance engine is that,a Jag ?

It looks much higher performance than it actually is  8.8:1  It's BMW M70B50, 5 liter V12.  Had about 300hp/tq in 1988, hopefully a bit more soon
But I digress... Sorry iiAtlas!

[iiAtlas]

For what it's worth, I had tremendous success de-gunking my V12 pistons with a standard utility razor (the kind that are sold in packs)

Before the razor, rag, and brake cleaner:


And after

Wow, now THAT is an awesome job!  I feel slightly embarrassed about my approach this is my first batch of pistons so I really didn't know what to expect or if they were even salvageable.  Now I realize it was just carbon build up and an approach similar to that of my carbs would've been beneficial.  Live and learn I suppose!  And I thought four was bad...try 12! 

[sbeckman7]

I'll admit 12 was a lesson in patience I am not eager to repeat! It was about 30 minutes per piston.. Live and learn indeed!

[iiAtlas]

Valve time!  Before I dive in I thought I'd get some opinions on strategy.  My current plan is to plug the spark plug wholes (probably with the old spark plugs themselves) and pour chem-dip in the entire seats (circled below).



I'll let it sit for about an hour then go at it with a razor blade, and only a razor blade.  This sounds pretty good to me.  Now some questions...

• Valve springs in or out?  Is there anything back there I wouldn't want to get chem-dip on?  Would it be better to soak the valves individually out of the body?
• Any tools I can use other than chem-dip and a razor blade?

That should do it!  Still hunting for a source on OEM CB350F piston rings, no luck so far.  Going to order a smaller ring compressor tool so that I can put the pistons back in the block and do some measurements.  Looking forward to inching this along!

[seanbarney41]

Razor blade is not gonna work because there are no flat surfaces involved.  Red scotchbrite soaked in acetone makes for reasonably quick work of this...brass brush is good to have here too...but it has got to be BRASS, no steel bristles...

[iiAtlas]

Razor blade is not gonna work because there are no flat surfaces involved.  Red scotchbrite soaked in acetone makes for reasonably quick work of this...brass brush is good to have here too...but it has got to be BRASS, no steel bristles...

Saving me time already!  Earlier in this project I naively thought GREEN scotchbrite was the lightest...WRONG!    Will pick up some of the red variety.  Thanks for the tips.

[grcamna2]

Razor blade is not gonna work because there are no flat surfaces involved.  Red scotchbrite soaked in acetone makes for reasonably quick work of this...brass brush is good to have here too...but it has got to be BRASS, no steel bristles...

+1  I also like to use 'Berkebile 2+2 instant gum cutter' which is good and strong too;wear skin and eye protection !