Engine Timing

ddoan · Post by **ddoan** » Wed Jul 07, 2010 3:08 am

I'm closing in on the completion of my Dexta's engine rebuild. Over the years, I've restored a few cars (mostly Lancias and Fiats) and have always found that when you set up the timing marks, they usually return to original position every other rotation of the crank.

Well, here is a photo, taken last April, of my Dexta's motor, with all the timing marks lined up (note the chalk marks):

Today, I was replacing the injection pump, camshaft, and idler gear. Note the timing marks:

As you can see, the engine is a lot cleaner. Aside from that, the marks are set as they were in the previous photo, and according to the instructions in the shop manual.

Now, here is where the marks are after one revolution of the crankshaft:

And, after two revolutions:

The brainteaser of the day is, how many rotations of the crank does it take before the marks line up to the original timed position.

I turned the crank around a few times and never got the gears to line up again, but have been told that eventually they would do so. Is this correct?

Don

pjjms · Post by **pjjms** » Wed Jul 07, 2010 3:37 am

I had a Nissan like that a few years back. I needed to pull the head off and did not have a manual. I thought I would turn the engine over until the marks lined up just to confirm the correct position. I must have turned 40 revolutions but they never did line up. I ended up just pulling the cams out and working out the timing at assembly time.

jambug123 · Post by **jambug123** » Wed Jul 07, 2010 7:16 am

They should line up again in every 17 revolutions

Regards
James

Bensdexta · Post by **Bensdexta** » Wed Jul 07, 2010 10:20 am

I believe it is every 18 turns of the crankshaft.

It is quite easy to show by means of an excel spreadsheet. The crank gear has 25 teeth, camshaft and fuel pump 50 teeth and Idler 90 teeth. So exactly 18 turns of the crankshaft turns the camshaft and fuel pump exactly 9 turns and the Idler exactly 5 turns, so all the timing marks line up exactly. 18 is the minimum number of turns to achieve this. I think this is what the manual says too. Alot simpler to work out than an Enigma code machine, which used multple rotors.

Don perhaps you can do an experiment to confirm this?