Thread: HELP!!! V8 Won't Fire After Head Rebuild

Originally Posted by Tyresqueal

J

However, in my rush to get everything back together for a trip at the weekend (which didn't happen as a result of this issue), I think I may have screwed up the timing between the cam and the crank by 180 degrees. Is it possible to do this? My understanding is that the cam turns twice as fast as the crank so this could make sense. Any thoughts will be greatly appreciated .

Nope. 180 degree difference just means what was number one TDC compression will be number one TDC exhaust. Rotating distributor 180 degrees as well will solve this.

I had a friend rebuild a Holden 253 recently and it wouldn't start. Told him to check distributor wasn't 180 degrees out, a few days later he told me the cam was 180 degrees out and they pulled the timing cover off to rectify. Lot of work for no reason.

Originally Posted by Tyresqueal

Just changed out the head gaskets, cam and followers on my 3.9 V8 and I'm having trouble getting the old girl to fire back up again. I'm aware of the issues surrounding timing mark inaccuracies and I'm pretty confident that I've aligned everything up correctly.

However, in my rush to get everything back together for a trip at the weekend (which didn't happen as a result of this issue), I think I may have screwed up the timing between the cam and the crank by 180 degrees. Is it possible to do this? My understanding is that the cam turns twice as fast as the crank so this could make sense. Any thoughts will be greatly appreciated .

Basic check 101. Set the engine to where you think no.1 TDC should be by the timing pointer. Lift the drivers side rocker cover, then rotate the engine either side of TDC. You should see the valves on cylinder no.6 rocking equally. Cam rotates 1/2 a turn every crank revolution so if the valves don't rock there try 1 crank turn onwards. So if the valves for cyl no.6 are rocking at TDC your rotor button should be pointing at no.1 You can reset the dissy easily after this has been worked out.

Well that clears that thought - I guess I'm going to have to take the right rocker back off and check for movement on rocker #6 to ensure that I get #1 on tdc. If that doesn't work then I guess I'll be making myself a noose. Thanks for the advice guys.

or..

take the spark plug out of the number one pot.
put your finger over its plug hole and start turning the engine by hand on the alternator/fan.

when it starts pressurising you're on the compression stroke, wind it up till you hit TDC on the crank marker and then reset the HT lead sequence to suit where the rotors pointing.

to check TDC if you think the crank marker is out drop a long handled phillips head down the plug hole and wind the engine forwards when the screwdriver stops going up you've just hit/gone past TDC on one.

Jeez Blkight , "drop a long handled phillips head down the plug hole "
Whats that supposed to mean ?
Why not a short handled phillips head ? perhaps a long shanked screwdriver ? (handle length optional )
As for turning by hand , your engines must be real low comp to do that unless you pull all the plugs first . Its easier to have a mate just jog the starter LMAO !!!

yep, long shank, my bad...

and no doing it with the starter.

a ratchet on the alternator or turning the fan by hand will work just fine, Im fairly certain that IF I can turn over 12l 6 pot diesels this way that a piffling 3.9 petrol will be just as easy, just take it slow and the compression will leak down and let you turn it by hand.

Thats great we all got a good laugh out of that one thanks guys Im going down the shed to check the lengh of all my screwdriver handles

Okay all, the saga continues - checked that timing was on compression stroke and 100% certain it's spot on. Removed dizzy and refitted with rotor button lined up with #1 plug position on dizzy cap so static timing all spot on (don't have timing light for dynamic timing so that's a no go for now). Tried to start her again and still just getting the odd cough and still won't start.

After much banging of head against wall I decided to go back to the start diagnostics wise. Checked for spark at every plug with these fancy lights that fit between the plug and HT lead - strong sparks at all plugs, so moved back towards a fuelling issue.

There is a strong smell of fuel out of the exhaust, so I guessed that the engine was flooding due to timing issues, but as I'm going over everything again I thought I'd check the fuel pressure at the fuel rail (I fitted a new fuel filter during the head overhaul - and yes the "out" nozzle is facing the engine). I don't have a fuel pressure guage, so using a small (thin head, long shanked, short handled, and perfectly formed) screwdriver to press in the pressure release valve in the fuel rail I discovered the following....

With the ignition switched on I hear the fuel pump come on for a short burst and then go silent, but when pressing in the fuel rail release valve there is zero pressure and no sign of fuel.

With the lesser half cranking the ignition I get fuel spurting out the valve.

Could this be the cause of the dead disco and should I be looking at the fuel pump or the regulator as the cause of zero ignition fuel pressure at the rail????