Cylinder head skimming and Timing

[USASPRINTMAN]

Does anyone know if skimming the head throws off the timing?<br>
I am guessing OMK 172R has had a head job once or twice in its life.<br>
<br>
Well tonight, I set the timing at 4 degrees BTDC, instead of the factory 10 degrees. The pinking went away and the engine runs as smooth and quiet as a baby's butt. Well, you know what I am trying to say. She's also running much faster, too.<br>
<br>
I was so happy to have finally got the car over the hump and got that last bit of smoothness, that I treated OMK to a tank of 110 octane racing fuel (with lead) for a whopping $4.99 a gallon!<br>
<br>
Richard Truett<br>
<br>
<br>
<br>


<p></p><i></i>

[redrichie]

Surely the octane rating of the fuel has an effect on the timing?<br>
<br>
Mine runs better on normal unleaded than it does on super unleaded, but i am sure if i played around with the timing i could get it to run smoother.<br>
<br>
As for your original question, I would imagine any work on the head will affect the timing, and due to engineering tolerances, wear, and the quality/thickness of gaskets used, that even two unmolested engines would never have the exact same timing setup.<br>
<br>
I have found that the only way to get her running smooth as is to set up the static timing as per the book and the marks, then keep slightly moving the dizzy until that sweet spot is reached.<br>
<br>
Someone with more knowledge is bound to come along and blow all this out of the water though...<!--EZCODE EMOTICON START :rollin --><img src=http://www.ezboard.com/images/emoticons/roll.gif ALT=":rollin"><!--EZCODE EMOTICON END--> <br>
<br>
richie.

<p></p><i></i>

[MaddMart]

Skimming the head will effect the timing as the straight run on the timing chain will be reduced slightly. So I believe that retards the timing, as the camshaft would rotate anti-clockwise by a fraction.

<p>Martin<br>
<br>
<!--EZCODE LINK START--><a href="http://www.dolomitesprint.com/" target="top">www.dolomitesprint.com</a><!--EZCODE LINK END--></p><i></i>

[davepoth]

And skimming the head will up the compression ratio a bit, which will cause pinking unless the timing is retarded.

<p></p><i></i>

[iandollysprint]

I worked it out on a bmw head I had skimmed. The changes were miniscual and not worth worrying about. Head was only skimmed 4 thou though. If the head has like 20+ thou of it it may change things. I eventually had the slots on my bmw cam sprockets elongated to give +- 6 degree of change due to fitting sport cams with no original timing marks.<br>
<br>
Jigsaw do an adjustable cam sprocket for a sprint - £120 I believe which isn't cheap. Anyone elongated the holes on their original sprocket?<br>
<br>
Ian

<p></p><i></i>

[Jon Tilson]

does have an affect on valve timing as Mart says.<br>
Its best to time the cam accurately and a vernier pulley will accomplish this at a price. Best to check that TDC is accurate with a dial guage too if you are going this far.<br>
Then set the dizzy timing up when the cam is right as the dizzy timing is pretty adjustable.<br>
<br>
Unless you have a known baseline its difficult to say where you are...whatever works for you!<br>
<br>
Jonners

<p></p><i></i>

[KWM338R]

Ian, I did the same to my cam sprocket, I think I did it 4.5 degrees each way and added an offset dowl to hold it all in place and stop it slipping, much cheeper than a vernier wheel<!--EZCODE EMOTICON START :lol --><img src=http://www.ezboard.com/images/emoticons/laugh.gif ALT=":lol"><!--EZCODE EMOTICON END--> <br>
<br>
Cheers<br>
Mark<br>
<br>


<p>1979 Dolomite Sprint<br>
1972 TR6 (now breaking for spares to fund the Dolly)<br>
1993 Mazda Protege ($250 Winter Hack)<br>
2000 Mazda MPV (For Sale)<br>
<br>
</p><i></i>