My friend took me under his wing to show me how he lapped valves. He used a piece of older fuel line, about 6ā long and would stick it around the stem of the valve and twirl the fuel line in his hands kinda like youāre starting a fire. It allowed him to move the valve pretty quickly rotationally in both directions, while finely controlling the pressure he put on the valve and the seat and compound. Generally I learned you put a reasonable amount of pressure to get the compound to do itās best work but it takes a bit of time. It was tedious and took time but the gentle pressure and fine grit compound gave consistently good results.
I still havenāt gotten around to making a block-off plate, but I perform a leakdown test anyways and rebuilt my motor last month. Probably the same OTC leak-down tester model Eric mentioned.
Ended up only having like 1% loss at 100 psi initially (I swept the pressures and they all still measured roughly 1%), but then I ultrasonic cleaned the head, valves, getting all the gunk out of there, cleaned the piston-top, and lastly I put it back together with fresh gaskets and new springs. After all of that, I did a leakdown test again for it to read 2% at 100 psi. This was all on a cold engine so Iād imagine the losses would be even more minimal when its running.
Now that the holidays and my wedding is over with, I can get back in the garage and tackle my laundry list of projects (one of them being making a nice block off plate) Lol.
Iām going to make a leakdown plate to test heads before and after valve jobs. Debating between using a proper head gasket or milling an o ring groove and using an o ring to seal the head to the plate.
Thatās interesting. Did you turn the engine over a few times to redistribute the oil? Another thought is not just warm (after running) vs coldā¦ but ambient temp. Depending on your heating situation in the garage that might impact the reading. My garage for example can be 90F in summer, but itās 20F todayā¦
I think Iād go head gasket in case for some weird reason a leak from a warped head gets missed.
It was pretty cold that night, but I rebuilt the engine in one sitting so I doubt temperature had anything to do with the readings. Iām assuming the extra loss is from where I cleaned out all the carbon build-up in the combustion chamber. It was pretty bad.
TDC!!! A MUST!! Warped valves usually cannot be lapped back in adequately.
We raced something like 24 weekends last year and my kid is super tall (over 6-4). So when the motor was off just a bit, that big hole he poked in the air made it more obvious than most. We also had 1 brand new motor and 1 brand new head on our 2nd motor that I had to break-in. Which made me aware of some initial run issues we encountered on new heads.
Last year we were checking valves after 2-3 club weekends and before every regional weekend. Intake valves were usually fine, the exhaust valve was almost always the leak source.
I would do a quick leak-down with the head on the block and listen at the exhaust port or exhaust end. If I could hear it or if I got numbers more than 2% leak-down with it on the block, I would pull it apart and lap. After lapping I would bubble test the head and valve with some water and a VERY LOW pressure air source. Really high tech stuff I knowā¦wrapped gorilla tape around an air nozzle, plugged the end into intake and exhaust ports and fed it 3 psi air with the head upside down and water in the dome. No bubbles and itās good. Small bubble spot, lap some more. Bubbles around 1/3 or more, likely warp in the head or valve. New head, suspect the head. Old head, suspect the valve (TDC start rope pulls prevent this). If I had a severe leak I would cut the seats and lap them. If I could not clear the leak after 1 cut and some lapping I would toss a new valve at it and lap and could usually got a great seal.
Replacing a valve was needed on the new heads this year as the heads seemed to deform around the exhaust seat early in life. Typically after a I had a couple race weekends on a head I would toss the exhaust valve, cut the seat on the head, lap it, and usually have no more issues until my son forgot TDC a few times.
Now, if I had local access to a builder I would have sent at least 1 off. If I had local access to a dyno I would have checked my work. Since I had neither I suspect that I may have lapped too often in an effort to insure that my driver would not be suspect of the motor. Typical drivers, its never themā¦
Iām not buying the TDC thing, can someone go into more detail? I understand itās common practiceā¦
Is the thought that itās a spring metallurgy thing, or a valve seats thing?
The latter I just cant get my head around, the spring pressure is so light.
The real answer is the highest wear on a cylinder is the top ring reversal area. You can obviously get wear anywhere in the cylinder but that zone (tdc or just below) will have the deepest valleys from the rings changing direction under high pressure.
Also pretty common to have a lower leakdown on a motor before you pull it apart. Most likely the carbon build up was hiding some true leakdown numbers. So after you cleaned it and it got higher, you took off the old carbon and exposed the true shape of the seat.
Another thing I would like to do is tap the valves a few times while under pressure to force out any debris that might be throwing something off or just see where the valve naturally lands.
Yeah the exhaust side of the combustion chamber (I think it was the exhaust, I canāt remember) had a ton of build-up. I had to basically turn my ultrasonic cleaner into a hot tank to get the carbon to come off. I wasnāt able to get all of it, but I was able to at least get the ports and valve seats clean.
Weāll see how the engine does come spring time. This was my first time ārebuildingā a 206 engine so it was more of a learning experience than anything.
The main theory as far as I understand is that the valves and the head cool at a āmore similarā rate rather than when the valve is protruding.
Over time the difference in cooling can lead to a warp in the valve, or that it is more likely to occur vs the valve and head cooling down while contacting each other.
A hot tank is the industry standard for cleaning most engine parts. An ultrasonic is one of those things that your mileage may vary depending on what you buy. I used a couple over the years and always wished I had the coin for a more expensive one.
One trick I found was to use Amsoil Power Foam. Iād pull the head, valves out etc and soak everything in Power Foam. Iād lose some brain cells but not many to start with
The foam eats away a lot of the carbon. Not the best solution but a solution in addition to brake clean and ultrasonic.
Some are of the opinion that keeping carbon in the head is a good thing. Itās a polarizing topic. Same can be said for keeping some in the portsā¦again controversial.
Yepp. I have experience with both because I had to use both to get the combustion chamber clean haha
Few minutes in the cleaner, then brake clean on a rag, wipe/scrape some off, back into the cleaner, etc.
In general, i use brake clean when i want something cleaned quick. And the ultrasonic cleaner for when i want to drink a few beers while im out in the garage.
We also had 1 brand new motor and 1 brand new head on our 2nd motor that I had to break-in. Which made me aware of some initial run issues we encountered on new heads.
