new 2.5 engine over heating, please help!! Ignition timing?

Mexicoearly911 · 04-30-2015, 05:55 AM

Hello everybody

i just finish my 2.5 engine rebuild. It has 9.7:1 86mm je pistons and 964 camshafts by John Dougherty, it has a cis injection.

The engine is running very hot, it gets to 230f just running at idle

It has no air or oil flow problems. New thermostats, and oil pressure relief valves and its not running lean

I suspect ignition timing has not being set properly and have no clue of what the values for this engine should be

I please ask for your help

Regards

Eduardo

Flat6pac · 06:27 AM

Make sure your thermostat on the engine is a match for the dash gauge or the gauge you have if its not correct for the car.
If the gauge is pre 77 the sender has to be brass
If the gauge is post 76 you need the chrome sender.
Ignition timing should be 3 to 5 degrees before TDC
Bruce

Mexicoearly911 · 04-30-2015, 06:45 AM

Thanks Bruce

Does any one knows what should be the max advance for this engine at high rpm ?

wwest · wwest's Garage

Had that happen years ago the rubbing block for the points was so worn that the points were barely opening....

Lapkritis · Lapkritis's Garage

Engines tend to run hotter when new before they're broken in...

Mexicoearly911 · 04-30-2015, 07:52 AM

The points gap is were it should be

Mexicoearly911 · 04-30-2015, 07:55 AM

The engine was completely rebuilt

jpnovak · 04-30-2015, 07:58 AM

Do you have an external oil cooler?

Timing should be about 32-33 BTDC above 5K. That is a lot of compression for single plug so I would not go higher than this. You risk detonation.

I don't know what distributor you have so it is difficult to comment about idle advance spec without knowing if you have vacuum advance or not. I assume you took a 2.4 (84mm) out to 2.5 (86mm). Was this originally a 73.5 CIS motor?

Neel · 04-30-2015, 07:59 AM

Quote:

Originally Posted by wwest

Had that happen years ago the rubbing block for the points was so worn that the points were barely opening....

This severely affects timing.. In a 'point type' ignition, always set the gap, (most accurately with a dwell meter) first, then set the timing.. Recheck the dwell to make sure it didn't change.. Always use distributor lube on the rubbing block of the points to slow down rubbing block wear..

Mexicoearly911 · 04-30-2015, 09:12 AM

Jpnovak you are right about the engine. The cis system comes from a 2.7 35mm intake/exhaust ports. The distributor is vacum advance

jpnovak · 04-30-2015, 10:23 AM

What is your timing spec now? at idle? At full advance?

Is the vacuum advance or retard?

Time to get out the timing light and see where you are. You might want to map the ignition curve as a function of rpm so that you have a baseline and know for sure that your mechanical advance mechanism is working properly.

Neel · 04-30-2015, 11:57 AM

Quote:

Originally Posted by jpnovak

What is your timing spec now? at idle? At full advance?

Is the vacuum advance or retard?

Time to get out the timing light and see where you are. You might want to map the ignition curve as a function of rpm so that you have a baseline and know for sure that your mechanical advance mechanism is working properly.

Jamie is absolutely correct... If you can get the dizzy number, you can compare what you have to how the curve for your distributor is supposed to work.. Since your engine has been heavily modified, you may want to have one of the distributor guru's recurve it for you for the engine to perform at it's best.. BUT, as Jamie said, you got to find out where you are, first.. Many times things get 'over-analyzed'.. Back to basics, solves many a problem..

Steve@Rennsport · 04-30-2015, 01:29 PM

Also need to know what octane fuel you use as that really affects how much timing you can safely run,...

Mexicoearly911 · 04-30-2015, 07:45 PM

I'm using 93 octanes fuel.

Thanks all for your help!

Mexicoearly911 · 04-30-2015, 07:48 PM

Thanks Steve

Mexicoearly911 · 04-30-2015, 08:09 PM

This is my 1977 911 with a 1973.5 t engine. That is how i bought it

Thanks again for your help

T77911S · 05-01-2015, 02:53 AM

the points gap is not critical. set the gap and set the timing. i have done LOTS of testing with different gaps and idle timing and engine temps. when wwest's block wore, that retarded the timing. yes the more the timng os set retarded the hotter the engine will run AT IDLE. once youi start driving the temp should come down if you have good cooling.
all the points do is provide a path to gound. thats why the gap is not critical. the 10yrs i owned my 77s i NEVER used a gauge to set my points, just eyeballed it. i tried setting them narrow and i tried setting them wide, i never could tell the difference. i would guess there is a point at at which they are so wide the CD unit would not have time to charge at hi RPM.
the only thing i dont know is how much wear of the block changes timing. but thats not your problem.

check on what bruce said about the sending unit.
check your loop cooler to see if it is getting hot if you have one.
bad engine Tstat? can it go in backwords? i had to change one on my 77 and that is the last time i have had one out.