The Valve Lash Story

Jun 18, 2020

If you want to start an argument, walk up to a bunch of racers and ask the BEST method of setting valve lash on an engine – bring your chair and popcorn because it can be quite entertaining.

Hot, cold, running, dead silent, EO/IC, firing order, aluminum heads, hydraulic, solids, roller rockers or stock rockers – the list and variations are lengthy. Heck even this article will probably generate some heat just from people reading it. One of the main things that you need to do is decide what’s best for your engine. If it’s a mild, stockish engine then setting valve lash is probably not even a concern for you. But if you have a engine that is pushing the edges of stay togetherness then valve lash is an important art. It can also help you analyze whether the cam you have in the engine is the one the engine really wants for your current combination.

I used the EO/IC lash technique in the past and if you’re not familiar with it, it means Exhaust Opening / Intake Closing. The idea is that on the cylinder you are setting lash on, you watch the exhaust valve as you turn the engine over, either by hand or with a bump switch connected to the starter. When the exhaust valve just starts to open, you can then check the lash setting on the Intake valve. Next you cycle the engine again and watch for the intake valve to just start closing, then set the lash on the exhaust valve. All is good save for the fact that some of the newer “close-lash” cams and even the old Duntov cam for Small Block Chevy motors can leave you with valves that are a bit closer to the piston that you suspect. In most high performance engines the biggest issue is the piston chasing the exhaust valve as it closes down. Normal rule of thumb is that we want to keep about .100 inch between those two items.

My preference in valve lash setting is to bring up each cylinder to TDC, then adjust the valve lash on both intake and exhaust valves, then move to the next cylinder. Some people say that this takes much longer than the EO/IC method but I don’t think it does and you can use it on any engine, from a single cylinder unit to a 12 cylinder Ferrari engine. The catch for a lot of people is that they do not have the crank damper marked in 90 segments or they can’t read it very well. I have resolved that issue with a homemade tool and it allows me to set all of the cylinders on one side of the engine, then move to the other side and set all of those cylinders. It has shortened the time for a valve lash job and I find that I do it more often now which is certainly a good thing. Of course this is engine specific but for the cost of an old distributor cap, you can make your own tool.

Valve Lash Setting Tool

I took an old distributor cap and using a hole saw cut out the center of it behind the plug posts. I then took a parts marker and marked each post with it’s cylinder number on both sides according to the firing order of the engine. Once this is in place, I simply watch the distributor rotor and when it points to the cylinder I want to check lash on (or run a leakdown test on) I’m ready to go. I can be on one side of the engine and check cylinders 1, 3, 5 & 7 then move to the other side and check 2, 4, 6 & 8. As I said it goes fairly quickly. In the photo above, the rotor is pointing at the number 3 cylinder, which indicates that it is at TDC.

Keeping a check on valve lash in a performance engine can give you a warning that something is going wrong or even point out that something has gone wrong. Late last year, I ran the lash on one of our SBC engines and found that I had broken the exhaust spring on the number 2 cylinder the previous weekend. Just another item in your maintenance arsenal to help keep that expensive engine running it’s best.

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