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April 15th, 2019, 10:30 PM   #1
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Red face Fe450 2010 slow cranking no start when hot

My 2010 fe450 starts ok from cold. If I stop briefly or stall whilst out and hit the starter it fires up. If I stop for a break or 're fuelling for a few minutes it cranks real slow and won't start. It will bump start straightaway and runs fine. If I wait a few more minutes and try it spins faster but not enough. A few more minutes waiting and it spins faster and fires up. This is the same even with jump leads on another battery.

I've changed the battery, plug, plug cap, fuel filter. Checked the tap. Valve shims all in spec. Auto decomp looks to be working ok. Ran the starter on bench till hot(NO load) it's ok, is clean inside and resistances are ok. Cleaned up earth lead and power connections. Something seems to drag the starter power right down when its hot and slowly release as it cools?
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April 15th, 2019, 10:52 PM   #2
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I had a similar situation with the 570 -09, eventually after a lot of grief I changed the camshaft, and that was it, rather the decomp was not working properly.

Working fine cold, hot nope.
I could SEE it working having the cover off, so that is NOT a viable way to establish proper function.

Im thinking you could try reducing the exhaust valve lash to say 5 hundreds mm, if that helps, its the cam.
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April 15th, 2019, 11:11 PM   #3
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Think I had seen your earlier post. Thanks, I have been considering this but what foxed me was that it seems to get faster as it gets cooler until it's fast enough to light it up. I thought if it was the decompressor then it would be off or on.
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April 16th, 2019, 06:11 AM   #4
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As I understand things its not that its defect, it just doesnt push the valve open enough, ie if you reduce the valve lash it will be enough to find out if its the culprit.
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April 16th, 2019, 06:44 AM   #5
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Yeah I am warming to the idea. I will give it a try. Cheers
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April 16th, 2019, 09:41 PM   #6
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Just a thought , wouldn't valve lash be less when its hot meaning the decompressor lump on the cam lifts the valve better. My problem is the opposite ?
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April 16th, 2019, 11:16 PM   #7
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Decomp mean valve lift is decomp axle height over cam surface minus valve lash, ie to make the decomp lift the valve another 0.10mm -> reduce lash by 0.10mm.
Just pop a thicker shim in and see what gives
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April 16th, 2019, 11:49 PM   #8
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when the valves are hot doesnt the gap reduce ? making the decompressor lift the valve more. If the decompressor is working ok cold then the gap must be tight enough. Warming up would tighten the clearance and make the decompressor lift the valve more. That's opposite to what seems to be happening with mine. It cranks slow when hot?
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April 17th, 2019, 12:24 AM   #9
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It works the other way around, when the effects of bad decomp started showing I increased the lash (at service) and that made it impossible to start just running for a minute. Put the old shims back in and it was back to normal cranking speed most of the time. So the lash is critical when it starts to go south.

Why it doesnt show its ugly face with cold engine I dont know, this is why I recommend you do an empiric test to see if it has any effect, much quicker than trying to figure it out theoretically.
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April 17th, 2019, 12:45 AM   #10
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Thanks. I will try this. Thinking back I cured an earlier cold start problem by re shimming the exhaust valves back into spec. It's probably about this time the hot start has became an issue. There's maybe some balancing act between the two, once things start wearing. Thanks for your patience. (Plus I was hoping it wasn't a new cam at 200.) Cheers.
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