Posted on: March 9, 2009

(previously published as Sucking Wind in the April 1994 RootesReview)
by Curt Hoffman

Tech tips are all about learning from mistakes. Since I am a novice restorer I have had plenty of opportunity to make mistakes. The tech tips I wrote in the past shared my foibles; this one is no exception.

For those of you rebuilding your own engines I have a watch out for you, particularly if you are going to add after market goodies, or aren’t sure of the lineage of your engine and heads.

Two years ago I ended up with another basket case Tiger and decided to completely restore it. First because I enjoy rebuilding cars, and secondly because I heard someone else was vying for “most money spent at a United at Tiger Tom’s booth”- a time honored spot I think I hold.

When I rebuilt the engine I decided to install a lot of after market stuff to make it my childhood kind of car again. (Yes I saved all the stock items so I could bolt them back on if necessary).

I had a real pretty engine when I was done including high compression pistons, high lift cam. Weiand intake, four barrel Holley 4010, roller rockers, Tiger valve covers, etc. Everything was great until I started it up.

When I started the engine it ran real rough. I did the usual: checked timing, wires to proper plug, float levels, etc. Unfortunately, at this point my compression tester chose to fail which really threw a curve ball at my troubleshooting. I won’t confuse this story with that side trip figuring that one out.

I noticed one side of the engine was hotter than the other. At the rear of the car one exhaust pipe was actually cold. The plugs on the cold side looked like they weren’t firing at all. I was getting spark to that side and the intake ports were all clear and the carb was functioning. No amount of beer helped me figure that out with the engine in the car so out it came.

Calls to several sources were no help. I degreed the cam to insure it was the correct cam (it was), I checked the lift of all the lobes (also OK), and everything checked out absolutely dead on. This was a perfect engine in every way except for whatever caused it to not run.

A technician in one of our shops at work, who also happened to be the Vice President of our local Union, (I was beginning to discuss this with everyone at this point and since we were in the middle of contract negotiations I used the opportunity to increase my resource pool) told me to check for any gap between the heads and the intake manifold. A slight air leak could cause the exact symptoms I was seeing.

I pulled the heads, removed the brand new Fel-Pro gasket that I had installed previously without sealant, and checked the gap. If I pushed I could get maybe a .002″ in one side. It looked like the gasket was fairly evenly being crushed so I couldn’t see at all how this could be the problem. I did however take his advice and reinstall the gasket with same red silicone sealer on both sides of the intake gasket. I then drank a lot of beer and re-installed the engine with no faith in my solution. By the way, as you can tell from my previous tech tips, I have never been able to just install an engine once and drive the car with either of my Tigers. I’m getting real good at getting engines in and out.

Bingo! When I started up the engine next time the problem was gone. Both sides ran hot and the engine was smooth. Lesson for me: never install an intake gasket without some sealant. A slight, and I mean slight, mismatch in angle can cause an air leak even though it would appear that the gasket would take it up. Since the leak is a sucking leak you can’t feel it. The effect was to significantly lean out those cylinders and in effect cause them to act as if there was no firing. This is kind of a V-8 problem and I wouldn’t expect this same problem in a 4 cylinder straight up engine like in the Alpine. (Ed note: Alpines suffer from vacuum leaks too. See tip C20 – 1725 Engine Idle)

As an aside, when I got my engine running it shortly began running funny again and the carburetor stopped acting right. Turns out even though I flushed out the tanks, coated them with sealant, put all new gas line in, new filter, etc. somehow some mess got through and plugged the carb. I had to rebuild the carb with a new power valve, jets, etc. to get everything right again. It was really gunked up. It really surprised me with only 15 miles on the carb and everything new. I think now I’m set- the car made it to the local cruise night on October 1 40 miles away- it’s first solo flight with no problems. I’m ready for the United in 95.

Footnote to Curt’s tip:

While preparing my Tiger for the drive to SUNI II, discovered an unusual problem. My Tiger ran great while it was still cool, as soon as the water temperature gauge reached 160, it would misfire very badly. Rebuilding the carburetor (2 times), new plugs and wires, new points, checking timing, and replacing all vacuum lines didn’t fix anything!

Finally, with less than 4 days to departure – a friend suggested that my intake manifold gaskets were leaking. My engine has never been apart so I didn’t have much faith in his diagnosis. He said that to check for a leak, get the engine to the temperature that it misfires and then spray WD-40 through the nozzle that comes with the can along the edge of the intake where it meets the cylinder heads. If the engine stops misfiring, you’ve found it.

I had leaks at the rear on both sides of the intake manifold! Two new gaskets and my car ran better than it had in years. I suspect I’ve had a small leak which just gradually got worse until I really noticed it. Wish I had known about that tip a little earlier!  …..  Eric Gibeaut

Leave a Reply

Your email address will not be published. Required fields are marked *