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Old 06-03-2013, 10:47 AM
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Hot Start problems?

I just fired up my first restoration project this week, after about 11 months of rebuilding just about everything. Its a '77 porsche 911 with a Chevy 327 SB in it. Custom headers, a fairly high lift cam, 600cfm carb and HEI distributor.

After an initial tune, it runs well, and idles as well as can be expected with this cam in it. But my problem is once its up to temp, and I shut it down, it wont start again till its cooled right down. Any suggestions why? The starter spins the motor fine when its cold, and it does turn over when hot, just extremely slowly. I thought it might be the battery was weak, so I added a second battery for a test, but same result. The starter BTW is an aftermarket version of the porsche starter, mounted to the porsche tranny.

It makes it a real pain to stop for gas, because you have to sit there for 20 minutes waiting for it to cool down before you can leave.

Cheers and thanks.
Mike B
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Old 06-03-2013, 10:54 AM
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Not familiar with that kind of starter, but a heat shield may be needed. Just wrap it around the starter. I would try that first. Where is the solenoid located? Is it on the starter itself?

http://www.summitracing.com/parts/sum-350118/overview/
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Old 06-03-2013, 11:31 AM
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starter pics

Yes the solenoid is on the starter. Here is a pic of it, mounted to the tranny.
M
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Old 06-03-2013, 11:44 AM
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It sounds like it is def getting some heat from somewhere. I would wrap it first (pretty cheap and easy), also check the wiring to make sure it is away from any heat source. Also, where is the battery located? How far from the starter is the battery?
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Old 06-03-2013, 12:50 PM
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Sounds like the typical GM hot start problem. The main cause is excessive resistance in the circuit that operates the starter solenoid. This resistance usually results from a number of small things that add up - pitting on the contacts inside the solenoid, corrosion in the battery cables, dirty or bad ground cable, long cables, long wires from the solenoid to the ignition switch, pitted or worn contacts inside the ignition switch (and NSS or clutch safety switch if used), etc. Many people go the Ford solenoid route, but this is really just a band-aid since current still passes through the contacts in the GM solenoid. Be sure you have a high-torque starter as well as good wiring.

I'm not a fan of heat shields because they are only a temporary heat blocker. Depending on how long you run the engine, the heat shield will eventually heat up and pass that heat on to the starter. Worse, with the starter wrapped in a nice blanket, it will stay hot longer.
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Old 06-03-2013, 01:38 PM
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I too would list a heat shield of some sort as part of the puzzle for an aid and if you don't have room, perhaps shielding with reflective blanket material only on the side of the starter and solenoid that faces the heat source and leaving the remainder of the starter open to breathe and cool the best it can. Using stainless steel hose clamps as the mechanical mechanism to hold the reflector blanket in place. If you can form a thin steel shield, adding the reflective blanket to that instead of directly to the starter would be the better option.

I don't believe it was mentioned as to the battery cables routing, I assume the positive cable is going directly to the starter solenoid, but what about the negative cable ?. Some cars and am thinking in terms of the Japanese car makers were famous for using that little cable bolted to the car body and then another cable which also was skimpy at best went from the car body to the engine block. Too many connections and not a large enough cable when conditions are marginal. If it were myself faced with this problem, I would be very tempted ( assuming the cables you currently are using are nothing special ) to upgrade to a considerably larger cable size for both the positive and negative cables for reduced resistance. Connecting the negative cable to the block and covering the cables along the length where heat may warm them excessively.

Shield the solenoid wires from heat if that hasn't been done as well and then give it a test and see if you have gained on it.
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Old 06-03-2013, 05:34 PM
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Timing issue? How much initial timing do you have and what about compression? Maybe a separate ignition switch on the coil might be the ticket. You know what Imean? Get then engine spinning then hit the ignition switch.
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Old 06-03-2013, 06:12 PM
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I would definitely look into installing a remote solenoid. This really isn't a band-aid as joe states. Yes, current will always flow through the contacts the same way they do in a Ford starter. You lose the small starter wire that acts like a resistor once it gets hot. This is the major problem with starter systems that use the small wire directly on the starter mounted solenoid.

Another item that may help. MSD's new 6AL Programmable ignition box lets you set a retard while cranking. This may help if your initial is correct but still causes hard start problems once the engine is up to temp.
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Old 06-03-2013, 07:13 PM
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What was just mentioned about a possible issue with ignition timing, usually I have found an engine to crank over in a slow/fast motion as the engine is kicking back at the starter due to it not liking the timing and wondered if it did that or was just cranking in slow motion with nothing being noted like this ?.

One easy idea to perform that I believe should tell you if its timing or not, next time its exhibiting the same symptoms, disconnect power to the coil and if it now cranks over with much more authority you will know its spark timing preventing the engine to turn over properly but if its still barely dragging its butt with no change in sound then its probably back to the heat issue.

I agree also with the idea of installing a remote solenoid away from heat, then run heavier gage wires such as 10 gage for example from the battery to the solenoid, then to the starter solenoid as this idea can only help, sure can't hurt as the cars wiring system may not like the draw of this starters solenoid although I would select a somewhat lighter remote solenoid then a true ford starting system unit. This sort of a setup is very common on larger diesel engines for a ignition key controlled trigger solenoid to power up the actual solenoid on the starter due to the amount of amperage that the starter solenoid demands in such a large starter.
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Old 06-03-2013, 08:15 PM
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timing

YES, Northern it does sound like that. When cold the cranking is smooth, constant rpm, but when its hot, it cranks slow but very erratic, sometimes it almost stops, then make a few revs then stops again. Weird sounding, like the battery dies, then wakes up again, and then dies again.

So please explain what the timing could have to do with this? Is it too far advanced during cranking? and why should the timing differ between hot and cold engine? The only difference I can see it that the choke is open when its hot. Another thing is that there is an electric fan, which runs when its hot, so maybe that is drawing down the current. But again, it doesn't explain the speed variation during cranking when hot.

Thanks to everyone who has posted help. BTW, how to I add a "thank" to a thread reply?

Cheers
MB
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Old 06-03-2013, 08:33 PM
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Old 06-03-2013, 08:40 PM
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In a word, timing could very well be your culprit but I'd be a poor person to ask to explain why an engine responds differently to timing based on heat of the combustion chambers as I can only speculate that the fuel volatility changes with the heat and may light faster. What you are probably experiencing then is kick back in an engine that wants to run backwards on certain cylinders. I suppose its always possible that its pre igniting due to high compression or hot spots and has nothing to do with timing but these are all items I'll let an expert speak up about. I would however do a trial test by disconnecting the coil power when it does this and see if it changes anything as that would at least tell if its the spark plugs firing too soon that is the culprit or if its another cause which is lighting off the cylinders too soon timing wise.
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Old 06-03-2013, 08:43 PM
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Quote:
Originally Posted by smikeb View Post
YES, Northern it does sound like that. When cold the cranking is smooth, constant rpm, but when its hot, it cranks slow but very erratic, sometimes it almost stops, then make a few revs then stops again. Weird sounding, like the battery dies, then wakes up again, and then dies again.

So please explain what the timing could have to do with this? Is it too far advanced during cranking? and why should the timing differ between hot and cold engine? The only difference I can see it that the choke is open when its hot. Another thing is that there is an electric fan, which runs when its hot, so maybe that is drawing down the current. But again, it doesn't explain the speed variation during cranking when hot.

Thanks to everyone who has posted help. BTW, how to I add a "thank" to a thread reply?

Cheers
MB
Excessive initial timing- which is often needed when using a radical cam- can cause the hot start problems you describe. One way to deal w/this is to use an ignition interrupter switch. More here.

You can also take a look into using a remote solenoid.

Good luck- sounds like a real fun ride!
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Old 06-04-2013, 03:52 PM
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Quote:
Originally Posted by joe_padavano View Post
Sounds like the typical GM hot start problem. The main cause is excessive resistance in the circuit that operates the starter solenoid. This resistance usually results from a number of small things that add up - pitting on the contacts inside the solenoid, corrosion in the battery cables, dirty or bad ground cable, long cables, long wires from the solenoid to the ignition switch, pitted or worn contacts inside the ignition switch (and NSS or clutch safety switch if used), etc. Many people go the Ford solenoid route, but this is really just a band-aid since current still passes through the contacts in the GM solenoid. Be sure you have a high-torque starter as well as good wiring.

I'm not a fan of heat shields because they are only a temporary heat blocker. Depending on how long you run the engine, the heat shield will eventually heat up and pass that heat on to the starter. Worse, with the starter wrapped in a nice blanket, it will stay hot longer.
You can use this setup and it's simple. BTW: any 30A relay can be used. It's a matter of cost who's cheaper, Any GM starter can benefit is circuit. I used it my Chevelle. The best part is the relay coil draw's MA instead of amps from solenoid coil. It will dump the full 12V to the S terminal from the relay contact. [IMG][/IMG]

Last edited by lg1969; 06-04-2013 at 04:04 PM.
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Old 07-31-2013, 04:39 PM
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Fixed!!

I managed to work around this issue by adding a time delay relay to the ignition wire on the Distributor.
Got it from Wolstentech online. It just delays the ignition by 2 seconds to let the starter get the engine up to cranking speed, before the high advance timing tries to kick it backwards, fighting the starter.

Cheers and Thanks for everyones help. Now onto bigger problems, smoke.
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