[NoVa-Corvairs] Noob May Need a Good Used Head
Dan Weiss
dkakd at aol.com
Sat Mar 4 10:55:16 EST 2017
Frank (et al),
I imagine you must have a dent in your forehead from smacking it with the palm of your hand every time you read something I have written. I assure you I have one from reading the replies and then realizing what I have written! After I read your explanation, it was clear to me that by going by the position of the rotor, I was putting the cylinder again in the combustion phase. DOH! Missed that the first time, but mistakes are opportunities to learn and grow with the proper guidance. The forest and the trees...
So I turned the harmonic balancer (effectively the crankshaft?) 360 degrees and checked the rotor and it was now 180 degrees from #2 cyl and positioned at #1 cyl. Ran the leak down again, and got essentially the same results, about 67% leakage out the exhaust. I think one of the valves on the meter is a bit funky as air doesn't always flow. There seems to be a sweet spot on the connector going to the cylinder hose that needs to be found..
This lead me to the following question; since the timing marks are for #1 cyl (correct assumption?) then wouldn't setting the #1 cyl at 0 TDC put #2 cyl in the proper exhaust position? I know this is no longer relevant to the need to remove the head but only to my understanding.
Truly a baptism by fire!
Thanks,
Dan
-----Original Message-----
From: FrankDuVal via Novacc-list <novacc-list at corvair.org>
To: novacc-list <novacc-list at corvair.org>
Cc: FrankDuVal <corvairduval at cox.net>
Sent: Fri, Mar 3, 2017 10:56 pm
Subject: Re: [NoVa-Corvairs] Noob May Need a Good Used Head
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>
To: Northern Va Corvair Club <novacc-list at corvair.org>
Cc: Bryan Blackwell <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> 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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