Thread: finding TDC on a flathead

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Join Date: May 2010
Location: lake Havasu Az
Posts: 25

Finding Top Dead Center
I recently had to confirm TDC and recalled a similar method I saw on another site. I just went a step farther and used a cc vial with ATF for my fluid. Rocking the crank back and forth until you see the highest mark in the vial and you will be on TDC. This matched the pointer I had set up when building the engine ( dial indicator with head off). I was just confirming the mark after 3 years of running. It works!!!
Dick in Havasu

since the piston resides at tdc and bdc for several degrees of crank rotation, you can be off several degrees with that method

and if you happen to be doing it on the overlap stroke, you will not only have a mess in your exhaust but on a flathead can creat a hydraulic lock in one of the other cylinders

I checked it several times and it always stopped on the same mark. That just happened to be where the pointer was set with a dial indicator. I do not understand how you can create a hydraulic lock with air? I am using the air to move the oil in the vial. If you have a better method, please advise.
Dick in Havasu

so I guess that you don't have fluid in the cylinder????

The proper way for absolute top dead center is to use a positive stop method where you stop the piston with a solid gadget turning the crank one way, and mark the dampner---then turn the crank the other way until it hits the same positive stop, mark the dampner---TRUE TDC degree will be in the exact middle of those readings

I don't disagree with that method. Tried and true. If fact I use it. Problem is, it doesn't work on a flathead. That is the only reason for the post. Sparkplug is not above the piston.