Briggs 5 HP- Timing marks way off, yet engine still runs!?

[creia]

1984 Briggs 5HP Model # 130202
OK, I am not the sharpest knife in the drawer compared to some of you pros. I'm just a garage hack that enjoys rebuilding/restoring the old Briggs flatheads. I am hoping that someone can explain this to me....
I recently took this RUNNING engine into inventory. It starts, idles, and powers up fairly well. Upon disassembly, I notice that the timing marks on the crank gear and the cam gear were exactly 180 degrees off!
How can this be and it still runs?
OK gents, please educate this old timer...
Thank you,
Michael

[bgsengine]

Ummm how are they 180 degrees off? When you have it at TDC and both valves fully closed, timing marks should line up ... alternatively if you have it at TDC and both valves are in the "overlap" position , timing marks can still line up - in that case I'd be checking the crank gear to see if it is keyed to shaft or cast into the shaft, and then I'd line up the cam timing mark to the crank where you'd normally be assembling it (TDC both valves closed, cam lobs pointing "down" away from tappets) and see if there's any faint timing marks - It could easily be a coincidence that you have a casting defect or chip in the camshaft gear that *looks* exactly like a timing mark, but isn't (I have had that happen before, except it wasn't "in time") However, timing crank to cam if it runs perfectly well, then 180 degrees means it's still in time, just wasn't timed at the right spot..

[creia]

OK. I was in error.
I'll call it a "brain fart", "senior moment", or whatever.
When I first removed the sidecover I saw that the timing marks on the gears were exactly (and I mean EXACTLY) 180 degrees off, but I failed to realize that the engine was not on TDC!
Boy, do I feel DUMB....
I just reinstalled the crank, cam, (timing marks aligned properly), tappets and set the valves in place and rotated it to (compression stroke) TDC- everything is as it should be. (no surprise)
Sorry for the useless post, however, thanks Brian for your reply.
Michael

[KE4AVB]

It just you had a senior moment forget how a four cycle engine works. Plus you got there is two TDC on four cylce. Normally you are timing on TDC compression stroke.

Okay this would explain it. The crankshaft makes two complete rotations to every one complete rotation of the camshaft. Otherwords it is a 2 to 1 ratio. I also use to work on form bursters that ran the input rollers at half the speed of the output rollers. Again a 2 to 1 ratio just snap the continuous forms into individual pages.

This way you get a four cycle engine by having the camshaft rotating at half the speed of crankshaft.

And believe or not you can have the timing off by one tooth and the engine may run even better; just depends which it is off by one tooth. Basically you are shifting the power curve. I have done auto engine where we offset the camshaft by it is keyed to improve the performance one way while hindering the engine performance in a another way. But I prefer to use variable duration lifters instead. Give both low end and top end perform at the same time.

[creia]

Thank you KE4AVB!
Yes, when i saw the timing marks opposed 180 degrees it was on the (non compression) TDC stroke. The thing is- I KNOW better!
Michael