Crank Timing Wheel

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FiatRally
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Crank Timing Wheel

Post by FiatRally » Wed Feb 27, 2013 7:15 pm

I would like to make a degree wheel to use on most Fiat Twin Cam engines.
What will be the most important Degrees to have on this wheel?
Obviously TDC and BDC has to be on the wheel. Then 40 deg and 80 deg as well as 110 deg and probably 55 deg.

Any help will be appreciated!
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Guy Croft
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Re: Crank Timing Wheel

Post by Guy Croft » Fri Mar 01, 2013 6:00 pm

If this is for checking with the engine running the only ones you need are for ignition.

so, cyl 1 use markings from 0 deg (TDC) to 36 deg BTDC with 2 deg increments. Large marks for the 10, 20, 30 deg points and smaller ones for the 2 deg points. No point doing one degree marks you will not be able to see anything that small with a timing light, anyway timing is always quoted +/- 2 deg anyway. In the case of the 8V Fiat TC engine optimum max advance at peak torque is 34 deg +/-2deg (Fiat data). 16v and SOHC 8v units have higher burn rate and need a lot less.

Most engines in the range have either 5 deg or 10 deg static advance so it would be a good idea also to have large marks for 0, 5 and 10 deg.

Cam timing check timing marks would require so many marks I would not put them on. The owner can easily stick a protractor to the front pulley.

If this is for engine building timing checks not running the engine a protractor is all that is needed so I assume you will invent some method of fixing this to the crank front pulley so it can stay on the engine?

Not sure!


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Urbancamo
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Re: Crank Timing Wheel

Post by Urbancamo » Fri Mar 01, 2013 7:37 pm

And if you have an adjustable timing light you only need true TDC marks and nothing more. And if you mark your marks straight to pulley, make sure to mark them to right side of TDC! Wich is the side clockwise from TDC.

I have always marked 0, 10 and required max. advance by engine type and I have been highly satisfied. 75% of my interest goes to max. advance and when the engine is running in 5000 rpm region in front of your face you wan't clear marks to see.
Generally Fiat TC distributors are well suited to competition engines too, you usually can use 10-12 deg. static and still your max. advance won't go off the scale (wich Guy mentioned)

-T
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Guy Croft
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Re: Crank Timing Wheel

Post by Guy Croft » Sat Mar 02, 2013 12:24 pm

not entirely true.

You can't use an adjustable timing light with twin coil distributors like the excellent Computronix and possibly distributorless dual coil (wasted spark) systems too, I am not sure - so it is vital to have the critical max advance mark on the front pulley. With the Computronix you can only read timing with the timing dial on the gun set to zero.

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FiatRally
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Re: Crank Timing Wheel

Post by FiatRally » Mon Mar 04, 2013 8:11 am

Good day gentlemen,

Guy thank you for the information. I want to use this on the front pulley of my engine to learn and understand the engine cam timing and will not be running the engine with this attached.

I do understand how to set the timing and have read and learnt so much on this forum! My pulleys have no timing marks left on them, as the person that cut them for me used the area where the timing holes are to seperate the inner and outer to make my pulleys!

I have set the cams by visually timing them and then using the dial gauge to set them up as per specification. The engine is now dry built. I need to understand the cam timing and angle of the cam boxes in relation to the cam position alot more.

I do not want to cut cams or change the cams I have, until I am sure what I want and what profiles I want to use.

I have the Abarth 068 Cam Profile to cut cams but am not sure if I want to use them.

Thank you Urbancamo,

Yes Before TDC is to the right hand side of TDC, I do understand. I am still very far from final build of this engine and will make sure I get the max advance right.

Static will have to be tested for best static once the engine is up and running in the car. Low rpm running will not be this engines main job. I will be looking at a high torque good revving engine.

7500RPM will be max and maybe even less! But good torque out of the corners and hard accelaration on the shortish straights will be important.

I am using the 1800 132AB1 block as the piston accelaration speed at TDC and BTC will be less than on the 2000. The stroke is shorter with the same bore as the 2000 block.

I have noticed that the same cams are used on various models. (South Africa and South America) Adjusted timings makes massive differences in power delivery and output.

The 125 models with the same cams adjusted differently was sold in South Africa and made less power than the Brazilian model. Adjusting the cams to the Brazilian specification made a big difference.

I have read and re-read GCs book in this regard so many times and still read articles about timing on this forum and still feel I do not know enough about the subject!

An engine is a pump and airflow through it is key to power!
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Guy Croft
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Re: Crank Timing Wheel

Post by Guy Croft » Thu Mar 07, 2013 7:44 pm

That is a nice little post, good for you, Ernst!

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