[NoVa-Corvairs] Noob May Need a Good Used Head

Fri Mar 3 22:56:02 EST 2017

Um,, no. If you rotated the distributor rotor 360 degrees, you were at 
the same stroke. Remember, the crankshaft turns twice as fast as the 
camshaft, but despite the Corvair actually driving the distributor off 
the crankshaft, instead of like most every other engine out there in 
which the distributor is driven off the camshaft,  the Corvair 
distributor , like all 4 stroke distributors, turns half crankshaft 
speed, so 360 degrees of rotor is the same stroke of the cylinder's 
piston. i.e. when the rotor points to #1 spark plug tower, it is always 
going to fire the #1 sprk plug on the compression stroke.

You need to turn the crankshaft 360 degrees to get the two different 
strokes (end of compression and exhaust).

Frank DuVal

On 3/3/2017 2:47 PM, Dan Weiss via Novacc-list wrote:
> Ran leak test again.  First time at 60 % leakage.  Rotated rotor 360 
> degrees.  Second time read 66% leakage.  Air flow out exhaust.
>
> Would the 60% indicate the compression stroke, and the 66% the exhaust 
> stroke?
>
>
> -----Original Message-----
> From: Dan Weiss via Novacc-list <novacc-list at corvair.org>
> To: novacc-list <novacc-list at corvair.org>
> Cc: Dan Weiss <dkakd at aol.com>; bryan <bryan at skiblack.com>
> Sent: Fri, Mar 3, 2017 1:09 pm
> Subject: Re: [NoVa-Corvairs] Noob May Need a Good Used Head
>
> Bryan,
>
> Thank you for your input.
>
> If I understand your first point, I may need to rotate the nut on the 
> harmonic balancer until the rotor comes back around to the position 
> for the second cylinder.  Had not thought of that.  I have been 
> turning the nut clockwise.  Should manual advancing of the crank be 
> done in only one direction regardless of which one?  I read somewhere 
> that if you go over where you want timing marks to meet, you should 
> not go backward, but make another rotation. I know that the timing 
> marks are only for cyl #1.
>
> Yes, it has electronic ignition.  Everything in your middle point flew 
> over my head ;-}, but the above is pretty much all moot as to 
> diagnostics in this instance but great for my edification on corvairs.
>
> I would be reluctant to go through all the work with one of "unknown 
> history."  Clarks quoted $150 for good used heads, which several have 
> said is really high.  Any idea what it should cost to rebuild a head 
> and where to go?  One vendor quoted $1500 to rebuild both heads.  Does 
> "if it ain't broke, don't fix it" apply to the other head, or should 
> both be rebuilt at the same time?
>
> Apologies for all the questions, but really at the start of the 
> learning curve with this.
>
> Dan
>
>
>
>
> -----Original Message-----
> From: Bryan Blackwell via Novacc-list <novacc-list at corvair.org 
> <mailto:list at corvair.org>>
> To: Northern Va Corvair Club <novacc-list at corvair.org 
> <mailto:list at corvair.org>>
> Cc: Bryan Blackwell <bryan at skiblack.com <mailto:bryan at skiblack.com>>
> Sent: Fri, Mar 3, 2017 12:21 pm
> Subject: Re: [NoVa-Corvairs] Noob May Need a Good Used Head
>
> Hi Dan,
>
> A couple of thoughts:
>
> First, you're right, the head has to come off. The compression check 
> shows zero. On the leakdown test, it may just be you had it on the 
> overlap instead of compression, don't forget it's two engine 
> revolutions per cycle.
>
> One other bit - as I recall you have an electronic ignition. On those 
> you don't want to pull plug wires for the test, it's better to sneak a 
> probe down the boot on each distributor wire and ground the cylinders 
> one at a time.
>
> Finally, I've reached the point that I don't trust used unknown 
> history heads. IMHO, if the head is coming off, I want to put a 
> rebuilt one with fresh seats in it's place. In any case, you should 
> verify which casting numbers are on the engine so both sides match.
>
> --Bryan
>
> > On Mar 3, 2017, at 12:04 AM, Dan Weiss via Novacc-list 
> <novacc-list at corvair.org <mailto:list at corvair.org>> wrote:
> >
> > Pulling one plug wire at a time, removing the wire for #2 Cyl 
> produced no difference, so it seemed the problem was the same cylinder 
> the Ranch found in need of some attention.
> >
> > Compression test was done on each cylinder. First test was without 
> having throttle open (forgot about that); second test was with 
> throttle open for each cylinder. Open throttle produced a range of 2 
> to 7 additional PSI of compression.
> >
> > Here are readings:
> >
> > CYLINDER FIRST TEST SECOND TEST
> > 2 0 0
> > 4 143 145
> > 6 150 157
> > 1 140 143
> > 3 157 164
> > 5 151 156
> >
> > Onto the leak down test.
> >
> > Did the best I could to get cyl #2 to TDC by aligning the rotor 
> under the cap with the #2 contact. First attempts read close to 100%. 
> Further adjustment seemed to tighten things up and tests consistently 
> read right on the yellow and red section divider at about 71% cylinder 
> leakage. I made sure to turn the regulator so the gauge read 0% before 
> connecting it to the cylinder. The gauge immediately read 71% leakage 
> and stayed right there. I turned the regulator clockwise to allow for 
> airflow from the compressor, and the air was flowing out the exhaust 
> pipe. What surprised me was that if I did achieve TDC, with the air 
> leaking out the exhaust, I thought the rocker arm in the pic would 
> have been with the exhaust valve, but as you all already know, that is 
> the intake valve.
> >
> > Does it seem that the leak down test was done correctly?
> >
> > Obviously, regardless of the leak down test, the head has to come 
> off to be replaced or repaired. I plan to pull the valve cover off to 
> see what may be going on under there tomorrow or Saturday..
> >
>
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