Low compression - valve adjustment?

Hi all,

I have a 3000cc, 130hp Corvair in a 601xlb (bought, not built).  During my most recent condition inspection, my mechanic and I discovered the compression in two cylinders is 38-40 (the others are 66-70psi).

Using an inpsection camera, it looks like there's buildup around the exhaust valve.  We also heard air coming out of the exhaust pipe, which confirms the exhaust valves are leaking compression.

At my mechanic's suggestion, I ran Marvel Mystery Oil through for 16 hours, but no difference on the compression test.

Next up is I wanted to check the valve clearances, however I can't find any information in the WW engine manual I have.

Does anybody have any clue on where I can find what the valve clearances should be?  

Thanks

Dale

N601DR

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Replies to This Discussion

Permalink Reply by John Edwards on August 16, 2018 at 12:21pm

Hydraulic lifters in a Corvair Never need adjusting.

Permalink Reply by Dale Walters on August 16, 2018 at 1:42pm

Thanks.  Looks like I may need to get the valve job done

Permalink Reply by Ken Pavlou on August 16, 2018 at 6:19pm

You can try staking the valves and see if that breaks up any deposits the valve may be hanging on.  Do you have exhaust valve rotators installed?  If you're running 100LL are you using a lead scavenger additive?  I strongly suggest Decalin runup if running 100LL You can find it at ACS http://www.aircraftspruce.com/catalog/appages/Decalin.php  The Decalin works very well in preventing hard lead deposits.  If you decide to go ahead with a valve job I highly suggest contacting Dan and Rachel at Sport Performance Aviation https://flywithspa.com/corvair/

Lastly, if you're getting 130 HP out of your 3000 cc corvair let me in on your secret because my 3.3 L stroker is only rated 125 HP at 3300 RPM.

Good luck,

Ken Pavlou

Permalink Reply by Dale Walters on August 16, 2018 at 10:20pm

Hi Ken,

Thanks, I'll try that this weekend.  I'm not sure if valve rotators are installed or not.

Yes, I'm running 100LL.  I didn't know about the need to run Decalin until about 16 hours ago, which I'm sure is why the lead deposits formed.  I've been in communication with Dan at SPA today.

I'm not sure how many HP I'm getting; that is what I was told by the builder.

Thanks

Dale

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