1984 70HP evinrude recently had heads milled .015

[64evinrude84]

I have heard horror stories of increased compression and temperature and engine failures after milling of heads. I blew a head gasket and had someone mill my head, they took .015" off and I thought that was alot. I have replaced the head gaskets and retorqued. I am contemplating my next step. What is normal compression for this motor and should I be thinking of richening up the fuel mixture or burning premium gas??? Also any good break in practices that I should consider??

 

[KYHunter2]

Re: 1984 70HP evinrude recently had heads milled .015

I really don't know for sure .

As all I've ever done is a very light sanding to true up heads . Then checked on a piece of glass.

I wouldn't think .015 would make that much difference.

At least not enough to cause damage.

That is as long as the pistons , don't hit the head.

If you do a compression test and its too high .

Maybe a set of low compression gaskets would get you back to even.

As I said I know it may raise the comp. some, still don't think it would be all that much.

If its only the head gaskets you replaced , no need for a break-in.

You will need to retorque , at 10 hours or so.

Personally, I do it at 3 and 10 hours , on a rebuild.

Really, my guess would be that if it runs well, with no piston to head contact.

I'd use same fuel / mix etc. and go for it.

The only problem I've heard of, that is similar ,.

Was caused by removing too much , and the pistons hitting the head.

KYHunter

 

[Dhadley]

Re: 1984 70HP evinrude recently had heads milled .015

.015 is a lot depending on which head you have on the 70. Be very careful. As a general rule of thumb we don't like to cut more than .010 off a recreational head. The problem is we don't know if it's been cut before.

Any time you cut a head you need to bolt the head up without the gasket and roll the motor over by hand. If the pistons touch, they're going to hit when it's running.

I would strongly recommend using the 332816 head gasket. It's slightly thicker and will help make up part of the .015".

The other thing that's happening (without the thick gasket) is now the spark plug tip is closer to the piston. Make sure you run the coolest Champion plug that you can. It might not hurt to richen up the mid and high speed jets slightly.

 

[Dhadley]

Re: 1984 70HP evinrude recently had heads milled .015

Sorry....double post....

 

[phillnjack2]

old topic I know, but needs to be cleared up....most advice above is pure nonsense..... you could cut 120 thou off and it still will not hit the pistons, its impossible.. the head on these motors is flat and the pistons DO NOT go over the top of the block deck.. 15 thou is not worth talking about.. you could get a brand new hc head from omc that was 50 thou thinner to give more compression.. now I have taken off 80 thou and have zero issues at all. with the head shaved you get better low down power and a touch more mid range.. your fuel will not even be noticed at 0.015.. so just bolt it on and go play.. once you get up to around 160 psi compression is when you need a higher octane fuel and possible re-jetting of the motor. . if you go look at those who are rebuilding omc 3 cyl motors you will notice most have around 50 thousandths shaved off, you have just 15 thousandths....... anyone telling you this will harm your motor has no idea of how these motors work..... only if you have the cylinder block decked /shaved do you ever need to worry about pistons hitting the head.. and 15 thou it would not happen......... just check your compression, normal compression 120 to 125 for a good strong motor.. over 160 psi needs high octane fuel

 

[Faztbullet]

.020-.030 is normal clean up on a lightly ring damaged head...adds maybe 3-5 psi