Corvair Forum

Anybody ever wondered what it looks like... This happened to a 140 I had going less than 15 mph at probably near idle.

Wowwwww......this isn't your main ride, is it Zach? Man, dropping the coin for those Porsche deep valve seats is looking better all the time.

Ouch...good pictures though. I guess this is a good reason to have deep seats put in the stock 140 heads I just picked up BEFORE I install in the car!! Thanks for opening it up and showing us the result even at low speed!

flat6_musik wrote:Wowwwww......this isn't your main ride, is it Zach? Man, dropping the coin for those Porsche deep valve seats is looking better all the time.

No it's not my main ride thank goodness. This is the first 140 I ever drove, built, ran, experienced. It was in my first Corvair too.

The story behind this....

I was just coming down of the hill from my parents to go to school or work. I'd probably only been driving for about 10 - 15 minutes. It was about this time of year so it was in the upper 50's temperature wise. The roads from the house are bumpy so I never go over 20 until I get to the freeway. I remember just pulling out of a stretch of trees and slowing down to go through the drain swell soft and easy and as soon as that happened....

BANG!... followed by multiple BANG!

Amazingly the engine was still running although powerless. The Banging had stopped and I imagine it was running on 3 or 4 cylinders. I pulled off the road and shut her down. Cranked it up to start again... still powerless and sounding a bit funky... lol

Walked home (1.5 miles and 1200 feet elevation rise) and brought the tractor down... pulled it home and parked it. Started it up again! (what was I thinking) and still powerless. Long story short I pulled the 140 engine and stuffed it in the garage and rounded up my 110 and built it up good... I did everything but split the block. That engine is tight!

My guess is the banging stopped when it had finished pounding the exhaust valve back through the head and had remelted the valve seat into compression head material.

BTW.. the crank still turns freely, the bearings feel very tight, the other valves appear to be in excellent condition and were well adjusted, and the pistons look great minus the heavy carbonization probably from the extra rich running after the seat dropped out.

Were you still is gear coasting down the hill? It's been said that a quick cooling of the head is enough for a seat to drop, from the rapid change in temperature.

I had one drop like that too, it also migrated into the adjacent cylinder, but not the next one after that... I'd just crested a long climb and haden't even started down the other side yet when wham wham wham.. etc. Looked very similar.

I lost a number 5 exhaust last year. Came out of Lowes, started it up. As soon as it turned over it was clacking. I let it run and after about 30 seconds, it slowly quieted down. I drove home with no issue, about 10 min away. I pulled the head anyway and found that the seat came out and than went back in. Not a lot of damage, thankfully.

So if I pick up what you guys are saying, there is no rhyme or reason to this. Or is there a preventive measures I can take?

I've never dropped a valve seat and I had a '65 Corsa as a daily driver back in the 80's that I drove fairly hard. I would say keeping the engine running cooler than it originally ran from the factory would set my mind at ease, not mention jetted just a tad "fat". Helps the drivability too.

Thank you that helps. I was getting kinda scared. I clean the oil cooler fins often.

I'd get in there and de-flash the heads too. Mine rarely climbs above 300 on the gauge, but as they are uncalibrated, it may be more or less.

I guess I don't know, what is de-flash?

De-flashing heads involves removing left-over material in the air passages of the heads. Sometimes, the left-over material will completely block the air passages. taking a hacksaw blade between the fins to remove this excess material can go a LONG ways towards keeping those heads cooler. Here's a couple of pictures I lifted from CorvairCenter showing a before and after pic of de-flashed heads. You do not have to remove the heads to do this, just (heh, "just") removing upper and lower shrouds so you can look down from above and see through the fins.
1st a "before" picture:


Now, "after":

You can see how much difference there is, much more air can flow through these bad boys and thus reducing all kinds of bad things that can happen, like dropped valve seats, pre-detonation, etc...

WOW that is a great tip, thanks Greg.

Whats the best way to do this? What tools are needed?