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Loud Knock?
Posted by: stephenjones20 ()
Date: August 28, 2011 11:02PM

I have a Fibertech buggy (like a Manx) and it has everything from a 1962 Corvair (suspension, engine, trans, even steering and such). It originally had the 80hp engine and I found a great deal on a 140hp motor, so I bought it and swapped it. Everything was running great after the swap(the buggy is street legal and I drove it 35 miles from my in-laws auto shop to my home). Then after the first 2 days at the sand dunes it developed a knock. When it's idling you can barely hear it, but when you rev it up at all it gets really loud. I took the belt off because it almost sounded like something caught in the fan, but it's still there. Any ideas on what it might be? I have a CHT gauge hooked up and the temperature is running right where it was before, and it still starts right up. One thing I did notice not to long before the knock started is that it began burning oil after it ran for a while, but it still has plenty of oil in it and I just changed it with a new filter before the swap.

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Re: Loud Knock?
Posted by: Tom Z ()
Date: August 29, 2011 05:47AM

..you've got a rod bearing problem,and probably rings or guides are causing the 'burning oil';; that 140 probably sat for too long,or was pulled because of those problems..

Tom Z,,Rochester NY

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Re: Loud Knock?
Posted by: stephenjones20 ()
Date: August 29, 2011 09:47AM

This might be a dumb question, but does that mean I need to do a full rebuild or what? I'm not to worried about the oil burning because it's not really smoking much and doesn't leak at all, but I'd like to get it working again if I can for not a lot of $$$. I do have the 80hp motor I pulled out of it, and a 1964 110hp? also that I can use for parts or it might even run (I got both motors from the same guy and he said it ran when he pulled it but that was also over 10 yrs ago).

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Re: Loud Knock?
Posted by: vairchet ()
Date: August 29, 2011 10:45AM

stephenjones20,

From your description: It sounds like a classic symptom of a connecting rod bearing that's failing. Once rod bearings loosen up from excessive wear, the shells will overlap and cause piston to smack the cylinder head. From that point, catastrophic failure is imminent.
As for the issue of burning oil: Either piston rings are stuck or broken. If they're broken, there's a good chance ring lands on piston are worn out or have broken apart.

Anyway you look at it, time for major repairs. Of course, you could jury-rig an engine together using mismatched parts. How long is that going to last?

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Re: Loud Knock?
Posted by: stephenjones20 ()
Date: August 29, 2011 11:28AM

I didn't think it would be "jury rigging" anything because I was told that the only real difference between the 2 motors was the heads and that if you put 140 heads on a 110 motor then it essentially makes it a 140. This is what I was told by the tech guy when I called LS corvair. Were they wrong?

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Re: Loud Knock?
Posted by: vairchet ()
Date: August 29, 2011 11:49AM

What I meant was swapping internal parts from one engine from another. In other words, piecemeal an engine together from a selection of used parts.

Yes, cylinder heads can be swapped as long as outer diameter of cylinder is compatible to both heads. '65 and up cylinders can fit either 140hp or 110hp cylinder heads.

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Re: Loud Knock?
Posted by: lgoodwin ()
Date: August 29, 2011 12:09PM

I hope you did not run the engine for more than 10 seconds without the fan belt.

I've never rebuilt a Corvair engine (yet), but the general consensus is that unless you are building a race engine or whatever, it's best to check all tolerances to determine what machining and parts are needed (not just "do it all up") and only replace the parts that need replacing and only machine the parts that need machining. Corvair engines are very long wearing, and machining parts that don't need it can have disastrous results due to the person doing the work not knowing the Corvair intimately and/or not being competent. Also, if you DO have any machining done, make sure ahead of time that you can get the necessary parts, like the correct oversize bearings and head gaskets, or you may end up with a worthless hunk of metal. Good Luck!

BTW, a guy in my club just torn down his 140 engine to find that the crank broken in two between #4 and #5 cylinders. He's trying to source a replacement crank. I gave him a list of vendors and suggested two people to help with the work (one local, one remote). I'd be interested to hear any good advice on finding a suitable replacement crank and how to properly prepare it to use in the target engine.

<table align='center' width='0'>
<tr>
<td><img src='[www.automation-scs.com]; alt='1962 Corvair 900 sedan' width='190' /></td>
<td><img src='[corvaircenter.com]; alt='1967 Corvair Monza 140/4-speed' width='190' /></td>
<td><img src='[corvaircenter.com]; alt='1968 Corvair 500 coupe' width='190' /></td>
<td><img src='[www.automation-scs.com]; alt='1983 Mexican Mustang 5.0' width='190' /></td>
<td><a href='[www.automation-scs.com&]; target='_blank'></a></td>
</tr>
<tr>
<td align='center'><font size='1'>1962 900 sedan needs a home</font></td>
<td align='center'><font size='1'>1967 Monza 140/4-spd</font></td>
<td align='center'><font size='1'>1968 500 coupe (now my son's)</font></td>
<td align='center'><font size='1'>1983 Mexican Mustang 5.0</font></td>
</tr>
</table>

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Re: Loud Knock?
Posted by: corventure Dave ()
Date: August 29, 2011 01:27PM

Corvair Knock 101..
A Stick shift.... when idoling, depress "disengauge" the clutch. If the knock goes away, you have a lose flywheel. It will sound a heck of a lot like a bad rod bearing.
Rod Knock... has the crankshaft been turned? 99% of the time they seem to be turned wrong! Shops almost never re-level and check their lathes after they are first set up.... sometimes it's years. I can't count the egg shaped journals I have seen over the years with so called good "turned" crankshafts!

Just some things to check.

Corventure Dave

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Re: Loud Knock?
Posted by: stephenjones20 ()
Date: August 29, 2011 09:33PM

I've tried the clutch already and that is definitely not the problem. It is coming from the engine for sure. With the earlier post someone mentioned only replacing the parts that need it. Does this mean that if it is the connecting rod bearings then I would just replace the bearings, or is there something else that would need to be replaced as well?

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Re: Loud Knock?
Posted by: zarfnober ()
Date: August 29, 2011 10:23PM

If you hear a very loud knock, someone is probably at the door.

Rocco

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Re: Loud Knock?
Posted by: Johnniespeed ()
Date: August 30, 2011 03:58AM

Until you take your engine apart, you will not know the extent of the damage. If indeed your knock is from a rod bearing, the crankshaft will usually have some type of damage. If your crankshaft has damage, the engine will require a full tear down.
The good news is that there still are good running Corvair engines around, if you dont want to rebuild yours.

John

1962 Rampside, 4.3 Vortec powered.
The thrill of speed overcomes the fear of death.

Sparta Michigan.


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Re: Loud Knock?
Posted by: corventure Dave ()
Date: August 30, 2011 09:14AM

Ok, good... the flywheel is eliminated. Just wanted to mention that for new-bees.
Next I would use a mechanics stethoscope to try to isolate what cylinder has the noise. Removing the engine fan and top cover will access the rod caps. From there you can check each bearing.

True story:

Many years ago I had a engine in a junker dune buggy with definite rod knock. The crank had been turned 10-10 by previous rebuilder. The bearing on #4 was warn far more then the others. Just replacing the rod bearing eliminated 80% of the rod noise, but as a junker I did not really care to fix it perfect. We got 5 more years of off-road abuse out of that engine before selling the buggy. Never had a peoblem with that engine.

Corventure Dave

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Re: Loud Knock?
Posted by: stephenjones20 ()
Date: August 30, 2011 09:24AM

That's what I'm looking for, it's just for the dunes and I'm planning on abusing it, but not to terribly. That's why I don't want to put a ton of money into a rebuild. I just need it to function properly and run well. The power before the knock seemed to be right what I was looking for, though the gearing could do with being higher (that's what I need to look into next is swapping in a 3.89 or 4.11 ring and pinion this winter). If I can get a couple of years out of it then I'd be happy with that.

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Re: Loud Knock?
Posted by: corventure Dave ()
Date: August 30, 2011 11:50AM

My buggy was a Automatic. Had to over fill the transmission by a pint to keep it from sucking air in hard turns and high rpm's. That's an old autocross trick with PG's. I had two brake pedals. Push both to stop. Or... one or the other to enhance a turn and literally pivot on one back wheel! Not fast in a drag but I could do donuts around a single fence post. Or one time a beer cooler!

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Re: Loud Knock?
Posted by: Claus ()
Date: August 30, 2011 11:54AM

Would it be an idea to pull one spark plug wire at a time, with engine running to determine that it actually is a bad rod bearing ?

Claus
Copenhagen
Denmark
Europe

1964 Corvair Spyder
1957 Chevrolet Belair
1964 Chevrolet C10

[www.flickr.com]


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Re: Loud Knock?
Posted by: MattNall ()
Date: August 30, 2011 12:02PM

Also.. have yo SNIFFED the oil?? for gasoline smell??

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Re: Loud Knock?
Posted by: stephenjones20 ()
Date: August 30, 2011 12:16PM

There's no gas smell that I can find. It seems like oil was coming out of the dipstick or something because it's only on the right side of the motor and I can see oil residue on top of the fan shroud around the dipstick, but when I check it's not overfilled or anything. The old 80hp burned/ leaked oil like a civ and this one doesn't leak a drop (yet). My real concern is the knock and if I can get that figured out I'll be pretty happy.

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Re: Loud Knock?
Posted by: MattNall ()
Date: August 30, 2011 12:48PM

Sounds like you may have just broke a piston.... easy fix with a used piston / rod from Calif. Corvair...


Just take a compression test / leakdown test or at least pull all 6 plugs and look for an oily one..

Then pull only that head off and then the cylinder barrel and you'll see..

MODERATOR
Sea Mountain, between Charleston Harbor and Coos Bay! SW Oregon Coast
Click HERE for My Website...Click HERE for My TechPages!
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Re: Loud Knock?
Posted by: stephenjones20 ()
Date: August 30, 2011 02:59PM

If it's a cracked piston that would show in a compression test? And if so you're saying I could just replace that one and be good, or is there something I'm missing?

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Re: Loud Knock?
Posted by: MattNall ()
Date: August 30, 2011 03:15PM

Nope if it's only one cylinder... all you need to fix to get it running again...


it doesn't take much to make a piston leak enough to get 0 psi compression..

MODERATOR
Sea Mountain, between Charleston Harbor and Coos Bay! SW Oregon Coast
Click HERE for My Website...Click HERE for My TechPages!
...............110-PG.................................................Webered-Turbo

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