Engine won't turn over when warm

[scottfab]

Originally Posted by Paul Workman

However, in retrospect, the problem with the arching is simply moved from the switch to the (mechanical) relay. So! I think I'll re-design the circuit and put a MIL spec solid state (FET) in place of the relay (read: no arching ever).

Not a bad idea as long as the FET is clamped with a zener to protect it from the inductive kick of the starter solenoid. (similar to class D amps).
Then, like any mods, it's a matter of documenting it well and in a place you'll find it if something goes wrong down the road. (or for the next owner) One of the biggest lessons I learned on custom mods was to document well. There's no amount of "oh I'll remember what I did here" that works

Originally Posted by Paul Workman

That said, Marc Haibeck made the comment once that he bypassed the clutch switch because pressing on the clutch puts a good deal of force on the thrust bearing in the LT5, a bearing that can be very dry, depending on how long it has been between startups. So... There's that to consider.

There will always be this pressure on the thrust bearing either before start or after. Failure will not be due to pressure on the bearing but the spin of the bearing dry which would happen regardless. (IMHO)

Originally Posted by Paul Workman

This discussion is warming to a tech article for the Registry, methinks!! But, in the mean time, I agree - we should be a smashin' da clutch afore turnin da key, doanchaknow!!

P.

Best overall solution would have been in the initial design. That is the NO (normally open) clutch switch in line with the high current starter solenoid is bad. Better would have been a NC switch in the gear lever at neutral. No one would be moving it while turning the key.

A noted and well know author and owner of a ZR-1 once said of the GM designers, "these are highly skilled, highly paid engineers that focused on these designs for years. They know more than shade tree mechanics." (paraphrased) That statement comes to me every time is see someone on this forum struggle with some of the more notorious failures. Fact is we've had decades now of experience that those engineers did not have. Improvements are not only needed but necessary for the good of the car. However, I've always made my mods "backoutable" just incase it's important to the next owner. (very likely after I'm gone)

[GOLDCYLON]

My cars pervious owner bypassed the switch because he was tired of having been towed to GM and the switch was replaced three times. He said the problem also occured after driving the car for a while. He would stop somewhere and then no start when he would get into to start driving it again. Always when the car was hot. Very simular to the OPs problem.

A large percentage of us have already done this becuase the switch is a POS. I am glad to hear a few members here have not had a problem. My arugment is its only a matter of time as it will happen at the most inconvient time in the most inconvient place and you be saying damn GC warned me. Im sure age of the componet, mileage and AZZ time in the cockpit all factor in here as to why the switch fails. Or you can just bypass it and when you car doesnt start you know what you can rule out. A no brainer if I ever saw one.

[Paul Workman]

Originally Posted by GOLDCYLON

My cars pervious owner bypassed the switch because he was tired of having been towed to GM and the switch was replaced three times. He said the problem also occured after driving the car for a while. He would stop somewhere and then no start when he would get into to start driving it again. Always when the car was hot. Very simular to the OPs problem.

A large percentage of us have already done this becuase the switch is a POS. I am glad to hear a few members here have not had a problem. My arugment is its only a matter of time as it will happen at the most inconvient time in the most inconvient place and you be saying damn GC warned me. Im sure age of the componet, mileage and AZZ time in the cockpit all factor in here as to why the switch fails. Or you can just bypass it and when you car doesnt start you know what you can rule out. A no brainer if I ever saw one.

Question: Do you know whether or not the previous owner turned the key and then pressed the clutch, or visa-versa (like should be done to avoid arching at the contact points)?

P.

[GOLDCYLON]

Originally Posted by Paul Workman

Question: Do you know whether or not the previous owner turned the key and then pressed the clutch, or visa-versa (like should be done to avoid arching at the contact points)?

P.

No idea Paul that was like 7 years ago. But he had to get the car towed three times back to GM. One can assume he was capabile of driving it and starting it. Each time they replaced the switch. He finally got tired of being stranded by it and bypassed it.

[Paul Workman]

Back to the starting issue for a moment...

FYI, A couple years back there was some chatter about the contacts inside the starter solinoid being a problem at about 40k miles (on average).

This is the relay that connects the battery to the starter windings - 100s of amperes involved, and is what is what starter "rebuild kits" consist of.

The contacts consist of a copper ring and two copper terminal posts. The copper ring (looks like a washer) is on a shaft that is slammed against the two copper terminals when the starter solenoid is activated to connect the battery to the starter windings.

At issue is arching. The result of arching is pitting and carbon tracing severely pits and etches the copper ring as well as blasting molten material from the surface of the copper terminals. Over repeated usage, the electrical connections deteriorate to the point where the starter will "click", but because current sufficient to turn the starter is not flowing, the engine will not turn over.

One can buy rebuild kits for the starter on ebay for under $10; consisting of a new armture & attached copper ring, as well as the two terminals.

(Note: One word of caution regarding some of those kits: The (plunger) pin on the armature may not be exactly the same length as the stock one. However, the copper ring of the stock armature can easily be resurfaced with some emory paper wrapped around a small (block of wood). Then, replace the terminal pieces and adjust them so that the ring contacts them both at the same time, and reuse the stock armature. (12,000 miles since I did mine and still going strong!))

This may have nothing to do with the issue at hand, but for anyone pulling the plenum for some reason, and hasn't R&R'ed the starter solenoid contacts, then would be an ideal time to do so!

FWIW,

P.

[Crusin]

Thanks for your opinion Paul. The issue was solved after I bypassed the Neutral Safety Switch. I am now in the process of trying to find a NSW for a manual transmission. CHEERS!

[Paul Workman]

Originally Posted by scottfab

Not a bad idea as long as the FET is clamped with a zener to protect it from the inductive kick of the starter solenoid. (similar to class D amps).

Hmmmm..... Well, that might work, but would have consequences. Due to the fwd bias threshold, in a situation where the starter is already "a bit finicky" (w/regard to minimum voltage requirements). I don't know if I want to put a healthy diode in series with the output. Maybe the simple "filter" capacitor (like they do on distributor/coil ignition) to absorb the "kick" might be sufficient, ya think?

Originally Posted by scottfab

There will always be this pressure on the thrust bearing either before start or after. Failure will not be due to pressure on the bearing but the spin of the bearing dry which would happen regardless. (IMHO)

I believe Marc is referring to the force imparted on the TO bearing to release the pressure on the clutch disc, which acts on the crankshaft via the flywheel when the clutch pedal is engaged. NOT pressing on the clutch would prevent this force from acting on the end of the crankshaft and the thrust bearing. Bypassing the clutch interlock switch would allow the motor to start w/o end thrust. Starter load would go up slightly as the transmission would be turned w/o the clutch being disengaged. (Prolly not so much on a DD, or even one driven once a week. But, once a month or less, and in the winter months especially? Makes sense.

Originally Posted by scottfab

A noted and well know author and owner of a ZR-1 once said of the GM designers, "these are highly skilled, highly paid engineers that focused on these designs for years. They know more than shade tree mechanics." (paraphrased) That statement comes to me every time is see someone on this forum struggle with some of the more notorious failures. Fact is we've had decades now of experience that those engineers did not have. Improvements are not only needed but necessary for the good of the car. However, I've always made my mods "backoutable" just in case it's important to the next owner. (very likely after I'm gone)

People aren't perfect, and bean-counters force engineering compromises to be made. Truth is where you find it, beit in some college level engineering course, or discovered by a "shade tree mechanic". Serendipity is a heck of a good teacher, I find!!

Back to the OPs question: All this said, I DON'T think it is the interlock switch anyway. I agree w/ scottfab. I suspect a connection issue (either internal to the starter or at the battery terminals or ground terminal). If it were the interlock, connecting jumper cables to the battery wouldn't result in it starting.

That said, electrical problems often will only show up when devices get hot. So, a cold starter might test OK, but after being heat soaked, things might turn up that weren't there before!

P.