1GM10 top overhaul

[abdiel]

Hi there, Im in the process of doing a top overhaul on my Yanmar, I have replaced the inlet and exhaust valves and guides. I have decided to polish the piston crown and the valves to
improve the flow of gasses in and out of the cylinder, but when the valves arrived they both have a black coating around the lower end near the seat. Is it ok to remove this coating or is it there for a reason? Thanks Abdiel.

 

[VicS]

I have no idea what the coating is but I would just lap them in and leave it at that.

Are you re-profiling and polishing the ports?

Are you expecting the boat to accelerate like s**t-off-a chromed shovel when you have finished

 

[abdiel]

Re :- 1GM10

Hi Vic, yes I am cleaning out the ports with a reamer and then a brass brush on a power drill. I am then lapping in the valves with the usual course?fine paste, and then if it is ok
polishing the valves for better gas flow. Im not expecting the boat to give me "water skiing" speed but just a little better efficiency. Thanks Abdiel.

 

[Niander]

Are you expecting the boat to accelerate like s**t-off-a chromed shovel when you have finished

lol

Yep you really are wasting your time but if it floats your boat...
I used to mess about tuning my Yamaha 2 strokes...think i did more harm than good!

 

[steve28]

i would be very cautious removing material from the exhaust port, its thin enough already.
With regards to the inlet and exhaust valves the coating is a by product from the hardening, i would pay attention to the height the valves as they sit in the head as this makes a considerable diffrence to the starting, they should be almost flush with the head surface when correct. The more they are lapped/ground in the more the compression goes down. Also the castings are renown for being porous so expect to be going down a bit or getting seats put in.


Steve