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My 250 crossflow timing needs to be advanced too far 

 

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 Post subject: My 250 crossflow timing needs to be advanced too far
Posted: Fri Jul 18, 2008 4:21 pm 
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:? Problem: I now have to run my ignition timing at what i estimate to be about 40 degrees advanced.

I used to run it around 14 deg, I recently replaced 450 vac carb with brand new 450 mech, fitted fuel regulator (5 psi), had head work done (lopped 055 thou, 2.5mm enlarged valves, guides, perf seat grind). I shimmed rockers accordingly to sink 30 thou into lifters (they should be between 20-60 thou).

Would not start, backfires through carb when flicking throttle. Changed dizzy, coil, leads, no change. Experimented and way advanced dizzy and she fired and seemed to run mostly normal. Bought a new timing light, mark in the same place way under water pump pulley at what i estimate to be around 40 deg advanced. Engine was freshly rebuilt and running at 14 advanced before I removed head and replaced carby.

Could this have anything to do with the jetting in the new carby? ie too rich so needs to fire earlier?? Valves being held open (I cleaned all lifters and ensured not broken or sticking)

I have done quite a number of rebuilds now on this and other ford engines and I am probably missing the obvious but I need some assistance.

Existing work done to motor. I was already running 450 vac, high lift/duration cam 35-75 extractors, standard rockers, anti-pump lifters, xe distributor module style, accel super coil, T5 manual trans, hi-tensile dizzy gear.

 

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XF Falcon, 250 crossflow, 450 Holley, Headwork/Valves, Mad Cam, 60 thou, Roller Rockers, V8 Radiator, Thermo's, Soon to be painted and T5'd... Has been painted and fully T5'd. Woo Hoo.

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Posted: Fri Jul 18, 2008 5:01 pm 
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could the cam be set on the wrong mark?? or the timing chain has jumped a tooth !!

failing that the dizzy could need to be recurved to suit the motor :)

 

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Posted: Fri Jul 18, 2008 10:24 pm 
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New timing chain/sprockets fitted when I re-built it. It ran fine a couple months till i decided to pull head an get it done. I have got two vacuum advance units, one rebuilt, one standard good condition. This is really kind of odd. It has only happened since re-fitting the head, and new carby shortly before. I'm gonna pull the jets out of the old carb and compare.

 

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XF Falcon, 250 crossflow, 450 Holley, Headwork/Valves, Mad Cam, 60 thou, Roller Rockers, V8 Radiator, Thermo's, Soon to be painted and T5'd... Has been painted and fully T5'd. Woo Hoo.

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Posted: Sat Jul 19, 2008 9:27 pm 
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With a cam like that, it would be wise to run Roller rockers. It saves the guides & valves. Can you get shorter push rods, better than shimimg the rockers.
Did you degree the cam when installing it???
Using MSD ignition will liven it up too.
Have you checked to see if the harmonic balancer hasn't slipped???
What comp ratio are you running???
This one was puting out 200 RWHP, with a 600 Holley & MSD ignition ( 6AL ). The vacuum advance was used, the dizzy was regraphed and ran at 14 BTDC at idle, about 850 - 900 rpm.

 

 

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Posted: Mon Jul 21, 2008 11:03 am 
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The pushrods I have are some moly type I picked up second hand years ago, they are the only ones I found (within my budget) that would not bend in the instance of an over-rev. As for the cam, I do not know how to degree it, I have aligned the zero and crank pulley as I have always done and the cam has been in the engine for 4-5 years, and ran fine after my last rebuild before the head work. Yes I also found 14 deg spark advance necessary. I am looking into an MSD asap. The balancer was fitted a few months ago with a perfect key and retaining bolt from the front. Comp ratio was just calculated at 9.5:1. I have got roller rockers in my shed I could put back on, once I have problems sorted out. I will double check the balancer but I make sure that stuff is secure when installed, it was only 800k's worth of running ago... Engine was only just run in before pulling the head.

 

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XF Falcon, 250 crossflow, 450 Holley, Headwork/Valves, Mad Cam, 60 thou, Roller Rockers, V8 Radiator, Thermo's, Soon to be painted and T5'd... Has been painted and fully T5'd. Woo Hoo.

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Posted: Sat Jul 26, 2008 11:34 am 
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It's going into the shop, gonna give it to a good modifed engine mechanic.
Hopefully he won't find any silly mistake I overlooked.

Will post the results to satisfy anyone's curiosity.
I'll put up a pic of my engine bay too!!

 

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XF Falcon, 250 crossflow, 450 Holley, Headwork/Valves, Mad Cam, 60 thou, Roller Rockers, V8 Radiator, Thermo's, Soon to be painted and T5'd... Has been painted and fully T5'd. Woo Hoo.

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Posted: Sat Jul 26, 2008 11:58 am 
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250_lover wrote:
It's going into the shop, gonna give it to a good modifed engine mechanic.
Hopefully he won't find any silly mistake I overlooked.

Will post the results to satisfy anyone's curiosity.
I'll put up a pic of my engine bay too!!


hopefully its something minor and wont cost you a packet!! :roll:

 

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Posted: Sat Jul 26, 2008 5:04 pm 
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My engine bay. Anyone see what is missing from the pic...

 

 

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XF Falcon, 250 crossflow, 450 Holley, Headwork/Valves, Mad Cam, 60 thou, Roller Rockers, V8 Radiator, Thermo's, Soon to be painted and T5'd... Has been painted and fully T5'd. Woo Hoo.

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Posted: Sat Jul 26, 2008 5:10 pm 
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Not the air-cleaner obviously...

 

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XF Falcon, 250 crossflow, 450 Holley, Headwork/Valves, Mad Cam, 60 thou, Roller Rockers, V8 Radiator, Thermo's, Soon to be painted and T5'd... Has been painted and fully T5'd. Woo Hoo.

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Posted: Mon Jul 28, 2008 9:36 pm 
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Where's the HT leads???

 

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Posted: Mon Jul 28, 2008 10:43 pm 
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who did you send it to?

 

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Posted: Tue Jul 29, 2008 7:39 pm 
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Yeah the leads, I wanted a clear shot of the rocker cover. Lol.

Gonna send it to Bob Freeman Motors in Townsville. His son Wayne has taken over and apparently he is pretty good. The bloke who did my head recommended him although I have been there for RWC years ago.

I know as much as most mechanics so need someone good who knows about worked engines who can diagnose it quick on the clock (bout bloody 80 bucks an hour).

 

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XF Falcon, 250 crossflow, 450 Holley, Headwork/Valves, Mad Cam, 60 thou, Roller Rockers, V8 Radiator, Thermo's, Soon to be painted and T5'd... Has been painted and fully T5'd. Woo Hoo.

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Posted: Tue Jul 29, 2008 7:41 pm 
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You got any better ideas Tickford_6. Just realised you were local.
I want to get this thing running sweet again...

 

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XF Falcon, 250 crossflow, 450 Holley, Headwork/Valves, Mad Cam, 60 thou, Roller Rockers, V8 Radiator, Thermo's, Soon to be painted and T5'd... Has been painted and fully T5'd. Woo Hoo.

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