Q: For those of you running EFI conversions...

drabels · 07-12-2017, 06:51 PM

...On your classic 911, with a modified ignition system which means you are no longer running with the stock (or any) distributor.

How do you do your valve adjustments?

The traditional procedure means finding TDC for piston #1, and normally the distributor rotor helps you find this.

What do you do instead?

I'm planning/contemplating an EFI conversion in the future for a project car, and I'd like to use Coil-on-Plug ignition. The thought just occurred to me. Hoping there's an obvious solution that I've overlooked...

tirwin · tirwin's Garage

That's a good question. I believe the Rasant solution uses the distributor for the EFI timing instead of a cam position sensor approach. Either way, wouldn't you have a TDC mark? As long as you had a reference then you should be able to look at the valves and make sure you're adjusting the right valve.

martyjr · 07-12-2017, 07:08 PM

Crank pulley marks at every 120 degrees following the firing order

martyjr · 07-12-2017, 07:10 PM

Forgot to mention that hopefully the pulley has the 120 degrees notches, sorry.

jpnovak · 07-12-2017, 07:54 PM

Not all EFI conversions require removal of the distributor. There are reasons to leave it in place (visual appeal) while removing the internal trigger methods and using something more accurate.

But... The crank pulley still has marks for valve adjustment. You can tell #1 from #4 TDC by the valve/rocker being at overlap or TDC. The valve covers will be off at this point and its very simple to perform a "wiggle" test.

drabels · 09:19 PM

Thanks guys. I guess I just had a "brain freeze" because every guide you read for valve adjustments always refers to the distributor.

Having another look at a typical four stroke cycle diagram, I can see that the distributor isn't really necessary as long as you can see/feel what's going on with the valve train.

A friend also suggested using a dial indicator in a spark plug adapter.

Edit: Found this, adds some clarity to the discussion I think.

http://performancedevelopments.com/valve-adjustment/

Adjustment is always done when the piston is at or near TDC on the compression stroke, or when both valves are closed. The camshaft lobes should be pointing away from the rocker arms.

Dr J · 07-13-2017, 02:10 PM

I did it by removing the #1 spark plug and inserting a hose from a compression tester or a leak down tester. Don't connect the other end of the hose to any tester. When you approach Z1 (mark for TDC on the crank pulley) if you hear or feel air coming out of the hose, then you are at TDC for cylinder 1.

turbobrat930 · 04:42 AM

If you have ever done a valve adjustment on a 911 engine, you really only need to look at the cam lobe of the cyl and valve you are adjusting. Just turn the engine clockwise (using the crank pulley bolt), and when the valve you are adjusting is fully closed (noted by the cam lobe being farthest away from the rocker arm face). Then you check the clearance with your feeler gauge and adjust accordingly.
I have NEVER checked for TDC on cyl #1. I just pull the valve cover off and do the exhaust valves first, then finish up on top.

And as Jamie pointed out above, you can always use the "wiggle" test to confirm the tension is off the rocker arm.

mysocal911 · 07-14-2017, 06:49 AM

Quote:

Originally Posted by tirwin

That's a good question. I believe the Rasant solution uses the distributor for the EFI timing instead of a cam position sensor approach. Either way, wouldn't you have a TDC mark? As long as you had a reference then you should be able to look at the valves and make sure you're adjusting the right valve.

It's hardly complex and obvious to most that a simple turning of the engine and watching the valves
move can easily determine TDC (compression stroke) of any cylinder, and thereby allowing for
an accurate valve adjustment.

Bottom line: Some overlook the basics!