just put my head back together. i had some pretty badly leaking valveseals in my #4 cylinder so i decided to replace them. i havent lapped valves in a few years, and last time i did it the engine was a internally stock z6, not my 500hp turbo engine. just wanted to get any positive or negative feedback on how it came out.

home made valve spring compressor. for what it is it works well, takes just a few minutes per valve to get apart.


exhaust valve before lapping.


an intake and exhaust valve after lapping. i was able to get the carbon and **** off the valve seating surface but was left with the dull grey color. did it have to be shiny?


the valve seats post lapping before i put the valves back in. do they look clean enough?


i think im gonna bolt the head back on with the old headgasket and do a leakdown to see if they sealed properly with the engine still on the stand rather than in the car

 

From what a can see (pictures not that great) they look fine. I would still have it pressure tested after you reinstall the valves and springs.

A DIY leak test for the valves, without the cams in obviously, with the head upside down, pour oil or water in the combustion chamber to fill it up, then somehow block of the ports and use compressed air into the ports and look for bubble coming from the valves into the combustion chamber.

 

to check them, I , turn the head on its side (int or exh ports up) with the valves and springs installed, pour mineral spirits or what ev in the ports and look for seeping past the valve/seat. flip over to other side, and repeat

 

^^ that is a good way to check, but you arent checking for leaks under pressure that way.

 

true, but what is going to seal the port well enough to get a pressure that matters?

 

This is what i do. I use brake cleaner sometimes though.

 

ok i flipped the head and filled the chamber. its been full for about 45 minutes and doesnt seem to be leaking i cant see anything dripping past the valves in the ports. ill check again in an hour once the heater gets the garage warm to work in. probably still give it a leak down to make sure

 

well it didnt really leak any fluid past the valves. i did put the head back on with the old hg. leakdown in that cyl was about 9% @100 psi which is right where it was prior to dis and re assembly, and consistent with the other 3 cylinders. seems good to me lets see how much power i can gain by switching over to tuner 1 cams from itr's...

 

do post the numbers after the cam swap. I used to have those but sold em

 

Will do. Im limited in hp to 525 to 550 due to my turbo size and fuel system, so ill probably make close to the same power I do now, but a little more effieiently with less boost

 

So do a lot of people reuse HG's?? I was under the impression that you wanted to change it out everytime you pull the head.

 

^It's good practice to change the head gasket any time you have the head off the block. Gaskets are ment to deform slightly when clamped between two pieces of metal, creating a seal. When you reuse an old gasket it has already been deformed and may not seal correctly the next time (especially with things like head gaskets which are subject to more pressure).

 

I thought the first heat cycle would mate the head to the block but people re use them....they are expensive I guess. or just use a sealer spray on it before putting the head on. ive only re used headgaskets on my dirtbikes

 

Yes I know to change the headgasket. At 100 bucks each for the 84mm ge gaskets I wasn't going to waste one to check if my valves sealed. Now that I know its good im taking the head back off, cleaning the mating surface and torquing it down again for good with a new hg.

 

OK. I wasn't sure. Because I know HG's are expensive. I plan to do a valvetrain swap with the head on the car for mainly this reason. LOL Because it would cost me $75 for another headgasket if I took then head off to do the work.

Good information though! Thanks for the clarification and good job doing your own lapping.