cylinder head question

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kingoftarmace2004
Posts: 102
Joined: Mar 15, 2018 3:34 PM
Location: Fall River Mills

cylinder head question

Post by kingoftarmace2004 »

since I have my engine apart and obviously the head is off. I was planing on doing a light lapping of the valves to insure sealing is up to par. I noticed that the valve seats seem to be chrome? just wondering if the lapping process is any different or if anyone here has experience to share? Thanks! -Paul
tn535i
Posts: 5357
Joined: Jul 14, 2006 1:30 PM
Location: Middle Tennessee

Re: cylinder head question

Post by tn535i »

A proper valve grinding (3 angles) at a shop is best of course. However, I've done the valve grinding compound method before. I had a 300k M20 that bent two valves and I put used valves in it. I used compound to grind them all just to make sure the seat and valve were unglazed in the approximate proper width of the sealing surface and they were close enough so I ran it. That was 7 years ago and I knew last year the car still ran.

The valve is hard material while the head is soft aluminum and so yes there is an insert in the head that is hard like the valve. Probably some chrome in that steel but it is not a 'chrome' part. If it is shiny it has been polished from use and a freshly ground valve or seat looks more dull and may even appear to have fine scratches in it. Same with cylinder bores, if they are really shinny and you cannot see the cross hatch from honing they probably should be honed.
tn535i
Posts: 5357
Joined: Jul 14, 2006 1:30 PM
Location: Middle Tennessee

Re: cylinder head question

Post by tn535i »

If you post some picture I'm sure some will suggest what they think. There are so many details to look at on an engine that is coming apart and mileage is usually the trigger for certain work but these motors are tough if cared for at all. By cared for I mean oil changes and never allowed to overheat.
kingoftarmace2004
Posts: 102
Joined: Mar 15, 2018 3:34 PM
Location: Fall River Mills

Re: cylinder head question

Post by kingoftarmace2004 »

Well the engine has 265k miles on it. but after full dissemble because of a bad transmission putting force on the crank to machine the thrust bearing into it. I have found date stamps of 97 on EVERYTHING. soooo im gussing this engine has been rebuilt if not a fresh factory rebuild back in 97. all I did was stud out everything. clean it all up/ paint bearings all the goodies. MLS headgasket and such. I will be posting pictures of the project coming along.
I think the valves have never been lapped so it was the original mirror surface from when the valve seats where installed and milled to spec. From my research and speaking to alot of machine shops I should be fine. Ive have done plenty of valves on cars that come through the shop. but have never seen a chrome looking valve seat. so it gave me a reason to pause and do some research! Thanks! -Paul
gadget73
Posts: 574
Joined: Nov 22, 2017 11:30 PM
Location: New Jersey

Re: cylinder head question

Post by gadget73 »

Whats the head like otherwise? The M21 is apparently prone to head crack issues.

Chrome plating is common on industrial stuff for wear resistance. Not sure how it does for the high temps in a valve seat though. Never fooled with AL headed engines that deep. If it looks good visually maybe just paint the valve with some marking compound, push it in the seat, and see what the pattern looks like. If its got good contact all the way around you're good.
tn535i
Posts: 5357
Joined: Jul 14, 2006 1:30 PM
Location: Middle Tennessee

Re: cylinder head question

Post by tn535i »

Hard Chrome is found in industrial equipment like hydraulic cylinders and such but you would not chrome or hard chrome something like a valve seat that is designed to be ground down to a fresh clean surface. And if like new it would not be shiny like chrome, more of a matte finish than mirror. If it is mirror like it is from many cycles of open and close that sort of hammered it smooth and polished.

Picture would be better but sounds to me like it should at least be lapped if not ground. Sliding surfaces like the cam journals in my avatar get highly polished. It should NOT look like that.
kingoftarmace2004
Posts: 102
Joined: Mar 15, 2018 3:34 PM
Location: Fall River Mills

Re: cylinder head question

Post by kingoftarmace2004 »

i will post pictures when I get a chance. i have some Prussian blue, just been toooo busy at the shop to work on my own projects. the head looks new. no cracks or anything, Even between the valves where its known for. something reallllly tells me its a factory rebuild from 97 with not many miles on it since. -Paul
kingoftarmace2004
Posts: 102
Joined: Mar 15, 2018 3:34 PM
Location: Fall River Mills

Re: cylinder head question

Post by kingoftarmace2004 »

okay not the best cell phone pics but i think it will explain what im talking about? -Paul Image Image
kingoftarmace2004
Posts: 102
Joined: Mar 15, 2018 3:34 PM
Location: Fall River Mills

Re: cylinder head question

Post by kingoftarmace2004 »

Image
kingoftarmace2004
Posts: 102
Joined: Mar 15, 2018 3:34 PM
Location: Fall River Mills

Re: cylinder head question

Post by kingoftarmace2004 »

damnit how do you post pics?
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