Chamber polishing: How much is needed?

N

Nitori

New Member
Do you really need a perfect mirror finish in your chambers or is something that's smooth to the touch good enough?

After getting my head soda blasted it was still a bit icky and pitted.
pcfW2qnh.jpg


Since this is a 100cc head going on a 125cc jug, I realize that the comp ratio is going to be a bit high anyways, so that pitting probably wouldn't do me any favors.

I put a set of old crispy valves in to protect the seats and wire wheeled some of the gunk off, but then it just looked even crappier, shiny but pitted. Flap wheel was too awkward and big to be much good either.

So now my dumb ass is sitting there hand sanding with 320 grit wet paper trying to smooth it all out...
RYwwjo1h.jpg


I gave up for the night after my hand got tired, but is it all useless without making this thing look mirror-reflective clean or can a quick pass of 600-1000 to "medium shine" do the trick?
Running a finger along you can't feel any roughness on the bottom part (opposite the spark plug hole) but still looks a bit pitted.
 
You're doing the right thing ;)
I would also consider having about .004(no more than that because compression will certainly be high enough) skimmed off the head surface because that corrosion is so close to the head gasket sealing surface.

To be honest,I'd personally not use that head because of the corrosion around that gasket sealing area..
 
grcamna5 said:
To be honest,I'd personally not use that head because of the corrosion around that gasket sealing area..
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Well this is the best head I have, everything else has bent fins or worse.

Also, the sealing area with a 125 cylinder is pretty much all outside of that edge pitting!
 
Nitori said:
Well this is the best head I have, everything else has bent fins or worse.

Also, the sealing area with a 125 cylinder is pretty much all outside of that edge pitting!
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That is fortunate about the sealing area :)
 
DohcBikes said:
Tell us more about your engine
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It's a 1971 Honda CL100 mill that had sat outside for a long time and seized. Jug and piston were totally trashed (Actually had to use a 100 ton shop press to separate them) so I got a CB125S jug and piston to replace it. I bored out the case to accept the new jug via hand, found another CL100 engine (sans jug and piston) to borrow parts from, got the whole thing soda blasted, and now am in the process of cleaning everything thoroughly in preparation of new case bearings, gaskets, and reassembly.


DohcBikes said:
and what the hell you are doing
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Opinions vary. :P Basically I'm making my best shot at a garage rebuild with minimal budget. I'm not aiming for max HP output, I just want to have a functioning engine that doesn't ping and lasts a while. Though little performance tricks here and there I'm willing to give a shot at, since spring is a ways off and I've got the spare time.
 
Got on it a bit more today, probably about as good as I'm gonna get it without a new head. Did 320 then 600 then 1000 just for giggles.

Here it is with my "good" valves in:
rm5I8bgh.jpg

What stumps me is those black "flecks." They look like nasty pits, but the chamber is smooth as can be- running a finger or fingernail over it you can't feel or catch on any imperfections.

I am still gonna take it to my friendly local machine shop and ask them to skim maybe a bit less than .004 off, then lap the valves in and be done with it.

Also regarding the gasket seating surface being pitted, I think I'm in the clear:

ZFoBZ62h.jpg
 
You've got the right idea :) That cylinder looks good after you had it blasted on the fins,I didn't recognize it !
Make sure to completely wash out the cylinder to remove all traces of grit.
 
Nitori said:
Opinions vary. :P Basically I'm making my best shot at a garage rebuild with minimal budget. I'm not aiming for max HP output, I just want to have a functioning engine that doesn't ping and lasts a while. Though little performance tricks here and there I'm willing to give a shot at, since spring is a ways off and I've got the spare time.
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In all seriousness... You have all you need to do done. Buy some lapping compound and turn it a few times with a cheap lapping stick (wood with suction cup at both ends) wipe it out good and run the Sharpie around and check it... You don't need to start a fire just a few short bursts spinning the valve in the seat. As soon as you see a perfect circle unbroken and even STOP.

Toss it together and run the vales a thou or two tight. New timing chain if it's even close to used.
 
Tune-A-Fish said:
In all seriousness... You have all you need to do done. Buy some lapping compound and turn it a few times with a cheap lapping stick (wood with suction cup at both ends) wipe it out good and run the Sharpie around and check it... You don't need to start a fire just a few short bursts spinning the valve in the seat. As soon as you see a perfect circle unbroken and even STOP.

Toss it together and run the vales a thou or two tight. New timing chain if it's even close to used.
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Sounds good to me. I'll be sure to get a new chain because both of the ones I have are of unknown mileage and about the best I can say about them is "they look shiny" ::)

I'm not quite clear on the sharpie method though- I know I put the sharpie on the seat, but am I spinning the valve a full 360 in either direction to check that circle? As opposed to the lapping motion where you're not going full 360, but turning 90 degrees often.
 
Yep make a pass with the sharpie then just drop the vavle in and give it a turn with slight presure, lift the valve and inspect the seat, if it looks nice and even, not a fat thin fat grind... run it. if it looks all wobbly your likely gonna need to recut the seats and grind the valves possibly need guides, i doubt that to be the case unless it was really junk to start with.

In this pic: you see 2mm of fresh cut, you don't need that much really just even and flat.

Valve_Seat_Width.jpg
 
I know it's a ghetto fix, but hey, a card of permatex is like $5 at your FLAPS, and a lapper is probably about the same.

The local engine builder place will A.) probably look at me like I've gone batshit insane for bringing in what's basically a lawnmower engine, and B.) Charge me $20 per seat.

A speed demon this is not. It's gonna be a fun little oddball bike though. 8)
 
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