460 engine problems
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460 engine problems
Hi all, got a problem that I hope someone can help me with...
I have an F-350 with a 460 big block carby on LPG and petrol. I have taken it to a few mechanincs as it has been losing power, but they can't pinpoint the problem. They say pot 8 isn't firing, plus pots 3 & 5 are erratic (no difference running hot or cold). I have changed the plugs, plug leads, dizzy and coil, but still no change in the problem.
Possible faults suggested by various mechanics could be... lazy valve spring (one mechaninc thinks this is not the case though) or a valley gasket fractured between 2 cyls, or valve stem guide, or broken cam lobe. Temp running normal, so broken head gasket unlikely. There is no difference in running it on LPG or petrol
Symptoms are as follows:
- Left bank running significantly hotter than right bank
- Significant loss of power
- Running very rough
- Very rich exhaust
Without taking the valley and heads off, does anyone have any ideas of what the problem could be and ways to confirm or exlude these.
Thanks...
I have an F-350 with a 460 big block carby on LPG and petrol. I have taken it to a few mechanincs as it has been losing power, but they can't pinpoint the problem. They say pot 8 isn't firing, plus pots 3 & 5 are erratic (no difference running hot or cold). I have changed the plugs, plug leads, dizzy and coil, but still no change in the problem.
Possible faults suggested by various mechanics could be... lazy valve spring (one mechaninc thinks this is not the case though) or a valley gasket fractured between 2 cyls, or valve stem guide, or broken cam lobe. Temp running normal, so broken head gasket unlikely. There is no difference in running it on LPG or petrol
Symptoms are as follows:
- Left bank running significantly hotter than right bank
- Significant loss of power
- Running very rough
- Very rich exhaust
Without taking the valley and heads off, does anyone have any ideas of what the problem could be and ways to confirm or exlude these.
Thanks...
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From: Niceville, FL.
Do a compression check and see what the readings are If some are low, squirt a litte oil in the low cylinders and recheck compression. If oil increases readings-suspect rings, if not valve, piston or gasket problem.
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Because 7 & 8 adjacent cylinders and with the firing order, this is a known problem with worn out cylinder parts and also a nother reason to seperate the plugs wires on the valve cover..so they don't cross fire.
do a compression test on each cylinder 7 & 8 with the adjacent spark plug in ....and than then ...out.
do a compression test on each cylinder 7 & 8 with the adjacent spark plug in ....and than then ...out.
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Thanks all for your replies.
Motor was rebuilt about 100,000 kms ago (so 62,000 miles)
Have done compression tests... all 160-170. Did the crossfire with 7 and 8 and still could not get 8 to fire and 7 not to fire.
A new development just come up is that it has read high temps a couple of times in the last few days... Don't know if this is a wiring problem will all the buggerising around that has been going on under the hood, or if it is really overheating.
I will open her up over Christmas and see how it goes.
Motor was rebuilt about 100,000 kms ago (so 62,000 miles)
Have done compression tests... all 160-170. Did the crossfire with 7 and 8 and still could not get 8 to fire and 7 not to fire.
A new development just come up is that it has read high temps a couple of times in the last few days... Don't know if this is a wiring problem will all the buggerising around that has been going on under the hood, or if it is really overheating.
I will open her up over Christmas and see how it goes.
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Joined: Mar 2005
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From: Redvers, SK
Does this motor have an EGR? If so, check the gasket between the EGR plate and the carburator. I had this blow out before, and it pumps exhaust into the intake, causing the motor to run like crap. If you want to check for an intake leak, spray either at the point where the intake meets the heads. If the engine speeds up, then its got a leak at that location.
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Posting Guru
Joined: Jun 2004
Posts: 1,635
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From: Niceville, FL.
I'd pull the valve covers an see if the valves on the cylinder(s) that are not firing are opening/closing properly. Sounds like more than one problem but I'd concentrate on getting all cylinders firing first.
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