Engine timing (strobe light)

[Leland Pate]

Ok, I want to use a timing light to set my ignition timing today.

I have a strobe light gun, and know how to hook it up now. I have read in my manual that on my '79 there are two timing specs. One taken with the vacuum hose connected and the engine @950rpm. The spec is 5 deg (+/- 2 deg.) BTDC. And a second spec for the engine speed @6000rpm and vacuum hose disconnected. 26deg. (+/-2 deg).

First off...what is BTDC?

Can someone give me a quick rundown of what I am shooting for here? I understand that I want a mark to line up with the crankcase and the strobe will alluminate when the #1 cylinder is fired.
What I am unsure of is this 5 deg. stuff.
And do I even perform the second spec. (engine @6000rpm) ? I was under the impression that revving the engine that high isn't good until it is good and broken in.

thanks, leland

[emcon5]

BTDC Is Before Top Dead Center.

The 6000 RPM thing is to verify that your mechanical advance is working properly. Whether or not that test is a good idea to run on a new rebuild, I will leave to the experts.

Tom

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82 911SC Coupe

[9eleven]

I'd vote for not doing the 6000 rpm check at this time.

As said above, that test is only to see if the mechanical advance is working. Its not really useful at all for setting the timing of the engine.

I'd personally just wait until its broken in until revving it to 6000 just to verify that the mechanical advance is working.

[john walker's workshop]

the 5°BTDC mark is to the right of Z1. you should get your full advance way before 6000. it's where the timing light doesn't show any more movement of the timing mark on the pulley as the RPM is raised.

[Leland Pate]

So, all I'm doing is pointing the light at the pulley and trying to get the notch just to the right of TDC to line up with the case marks.
I adjust the dist. housing until it is set, correct?
Sounds fairly easy.
thanks,

[Superman]

Yes, exactly, Leland. You loosen the clamping nut under the distributor and rotate the distributor until the 5-degree mark, just to the right of Z1, lines up with the stationary notch on the fan housing.

FWIW, my timing spec says my vacuum hose must be disconnected for this (idle) test. Yours may be different.

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'83 SC

[john walker's workshop]

easy. 78/79 hose on and idle 900-1000. 80-83 hoses off and turn idle down to 900.

[Matt Smith]

Leland, you are priceless. You have just completely rebuilt a Porsche 911 engine beautifully as your first engine rebuild yet you have never set the timing before? I am more impressed as time goes on!
Keep asking the questions; I'm sure you are helping countless people out here.
Just wonderful!

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'72 911 TE

[fred cook]

My 1980 911SC has vacuum advance and vacuum retard hoses. I have been disconnecting both hoses to set the timing (with timing light). At idle, the vacuum retard hose has about 17 inches of vacuum while the vacuum advance shows 0 vacuum. If you don't disconnect and block both hoses, the timing will be over advanced. By the way, Sears sells a timing light that has an advance feature that lets you "adjust" the strobe light and directly read the advance off a scale. Don't know what they cost now (have had mine several years) but they seem to work well. You can rev the engine to various rpm levels and take readings to get an approximate map of your distributors timing advance.

[emcon5]

Originally posted by fred cook:
By the way, Sears sells a timing light that has an advance feature that lets you "adjust" the strobe light and directly read the advance off a scale. Don't know what they cost now (have had mine several years)

I just looked at those a few days ago. IIRC they were around $65.

Tom



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82 911SC Coupe

[Leland Pate]

Matt, I know it must seem funny. I have a basic understanding of how cars work but as far as specifics I get a little confused. That's why you guys are here!
Hell, before this, I didn't know how to adjust my valves...and I rebuilt my own engine.

it did take me 9 months though.
Thanks for the clarification guys, it's cleared up things allot.

And you came close to hitting the nail on the head...I'm not priceless...YOU guys are PRICELESS!



[This message has been edited by Leland Pate (edited 09-19-2001).]

[Roland Kunz]

Hello

You need to raise the rev level when you brake the engine in.

In the old years the 911 engines wher broken in from the factory, you will find how in the Porsche workshopmanualls.

Reving is not a problem more WOT at low revs and long constant runs.

Grüsse

[RoninLB]

Leland...Your not confused, although you may be well mixed....Different timing lites may show a slightly different reading. When breaking in an engine you want to keep rings pressed against cylinder. I constantly rock with gas pedal always moving up and down which pushes rings out to cylinder. I did that for 500mi.never going into 5th gear, slowly raising rpms every 100 miles. I did this all on open roads till it became 4th gear at 3,500 - 4,000 for 100 miles. It is boring and you may get seasick but will wind up with great comp./blowby numbers and 2,000 - 3,000 miles per quart of oil. I changed oil filter after 1st warm up to remove rebuilding lube. There is more, if you like my act contact me..Keep Rock'en..

[Jdub]

Ronin brings up a very good point; remove your filters after a short run. Lots and lots of questionable material in there; swarf, heavy molys, etc. that need to be removed from the system. Case in point: I just pushed a chunk of carbon out of the Rside of a drain pipe on a '51 Triumph T100 engine that was preventing the exhaust rocker box from draining oil. It took me ONE YEAR to figure out why the exhust pipe on that side was oiling up but the 'plug looked perfect.

Cycling the engine is also a very good idea. These next 200 miles are critical in terms of seating your 'rings. You want those ring edges to never get totally comfortable, they ought to be jerked a bit around, deceleration on downhills, this sort of thing can help.

Timing is a breeze, but I get scared at the 6K rev. I must say.

Jw

[Jorgeman]

I remember back when the mechanic was doing the first check-up on my brand new '67 911S. In those days I could be in the garage right with him as he did the valves, etc. But when it came time to check the mechanical advance and automatic rev limiter that first time, he firmly "invited" me to wait outside because he knew I'd flip when he revved it up to around 6500 RPM's! It DOES sound potentially expensive when it's up at chest heighth on a lift and he lets it wail!

George 86T