wiggin

I was working on my timing, and was rotating the engine by hand. In order to check which stroke I was on I installed just one spark plug in cyl #1. I was shocked when i was still able to turn the crank during the compression stroke and could hear a hiss coming our of the spark plug hole.

I thought maybe this was an isolated occurrence on cyl 1, but tried a few others and had the same problem. These are some after marked Alum cylinder heads recently installed.

I did a compression test on the engine and each cylinder hit 160psig. But the compression tester has an oring that seals off the threads.

Are there special sealing washers i should use on alum heads that the manufacture didnt install or mention?

JakeJr

With only one spark plug installed, yes compression will be forced out of the other seven, that's normal. If you crank the engine with the starter you'll br able to hear and feel the "puff" sound.

Now if you installed the WRONG type plugs, they won't seal. There are basically two type of plugs, one type comes with a compression sealing metal gasket (looks sort of like a washer) and the other type type has a tapered end which seals against the head WITHOUT the need or use of a gasket.

You need to check to be sure you're using the correct type plugs for your heads.

Jake

Viprklr

iTrader: (5)

I don't know if this holds true across the board but my iron heads didn't use a gasket. My aluminum heads do use it.

Damon

If the hiss is coming from the plugs (not leaking past the rings- which can be difficult to tell where the sound is coming from), then you've likely got either the wrong plugs or forgot to install the crush washers your plugs came with.

Most atermarket heads these days (not all) use gasket-seat plugs with 3/4" thread reach and 5/8" hex nut. Autolite 3924 or equivalent is a common example. They come with the crush washers in the box with them, but you have to spin the washer down the threads yourself before installing the plug in the head.

Check with the head manufacturer for spark plug application to be sure, though.