thoughts on combustion chamber

picked up a 750 head in otherwise great shape, new guides, good threads... but am unsure about the combustion chamber, as there's some widespread pitting, the valve seats are in good shape and don't appear pocketed

opinions?

Smoothe it out with Emory paper and go on without a worry. It will not unduly carbon up.

I seized a piston 50K miles ago, and dinged up my left chamber. Recently pulled the head .... both chambers about equal carbon and not much at that.

Slick

i may have the chamber coated to arrest further corrosion

I would have thought the corrosion was caused by neglect, ie left open for a long time, should not corrode in normal use.

I would not mess with; run it as is. It looks like poor quality casting but should do no harm. It will lightly carbon up and be smooth; not that smooth is that important. I would not take any metal away from the combustion chamber is it will diminish your compression ratio.

This probably happened when it was cleaned or sand blasted. The same thing happened to me. I took in 2 heads for sand blasting. One came out fine and the other ended up like yours or worse - but there was no problem with the rest of the head being sandblasted. Don't sand blast it or subject it to any more severe cleaning - usually 750s.

I agree that the chambers are just as well left as-is, but, if you do decide to go ahead with a cleaning, drop a couple of used valves into the guides to protect the seats during the operation.

Nathan

thanks for the replies, I agree it likely occurred during sandblasting. I'll likely have the chambers ceramic coated as my only real concern is uneven heat transfer, which I'm told the coating should prevent, and possibly fill in some of the smaller pits

Say acadian, I doubt the ceramic coat will help with uneven heat transfer but it will reduce the heat transfer (i.e. keep more energy in the combustion chamber). Honestly, unless there's a problem I would not mess with it and run the cylinder head as-is. When you think about it, there are probably tens of thousands of Commando and Atlas engines that don't have a problem. I ran a Drouin supercharger back in the 70's with 10 psi boost and there was no issue with uneven heat transfer. There was incredible heat and I was really impressed with how well the Mk2a head and barrel handled it.

I've ceramic coated an ultra short stroke 750 and can't say there was a difference in performance though everything was a new build. Jim Comstock and maybe afew others might chime in on the durability of the coating as I recall some comments about it flaking off and going out the exhaust (or elsewhere)

If you want to ceramic coat something consider the intake tract where you want as cool an intake charge as practical but in all honesty, unless you are racing or trying to squeeze out some optimal performance, just run the head as is.

If you want to throw some money at your bike to enhance it, consider some lighter pistons, rebalance the crank to the new pistons and rods and get a quality valve seat job..........or invest in a Full Auto head and reap the benefits of decades of race development.

My two pence worth.

I would also be tempted to consider ceramic coating IF I had access to a competent firm. I have had quite a few different heads coated over the years and am a ‘believer’ I guess.

However, I’m the one who posted about the stuff flaking off in my last motor build, and the pot with the worst flaking was also badly scored, whether or not this was coincidence, or the ceramic medium caused the scoring, I don’t know.

It’s the first time I’ve seen such a failure though, hence my intital comment, if it’s applied correctly, it is sound. If not, well, it’s not!

Devcon for the deeper pits ? The epoxy would eventually turn to carbon. Even if it came out, it would be unlikely to cause damage.