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Loud clunk on start up

Old 01-05-2018, 09:49 AM
  #31  
911Ragtop
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Default Solved problem: new starter

Originally Posted by jvandyke View Post
super old thread but the question is valid, our '87 924s with fatty starter and ref. sensor shield STILL does this regularly, the starter needs to be replaced anyway but we replaced it once before and the kick back actuallly exploded the internal planetary gears, just blew them up, then we actually put the old starter back in. An after market gear reduction starter perhaps? $$$ It would seem like one could add another shield or something to address this
We found the problem. It was just a bad starter. When it finally failed and was replaced with a new “off the shelf” starter the problem was solved. No big deal just put a new starter on.
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Old 01-05-2018, 09:56 AM
  #32  
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I think a new starter might be less susceptible to the issue but we also swapped starters, problem went a way for a while, than came back and DESTROYED the starter, the kick back shattered the planetary gears. We put the old starter back in and went back to 50% kick back clunk. This starter is slated for replacement too as the nose piece is wallowed out badly, I added a bushing that has since been destroyed so nothing for it but another new one. Save your receipt!!! If your sensor wires are long, be sure they're routed as far away from the starter as possible, don't let them loop toward the left side of the engine but up and away as quickly as possible. We reinstalled the bell housing last night and need to do the sensor brackets and all those fun bits next.
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Old 01-05-2018, 02:48 PM
  #33  
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I've had the same issue with my early build '87 n/a (Nov '86 build date). I'm now on my 3rd starter in just over a year of ownership. According to my records, the previous owner was having the same problem in the first 3 months of ownership at 1,800 miles. The dealer installed the updated reference sensor bracket at that time, but the car has been through way too many starters for 65,000 miles. Each time I replace the starter, the problem becomes less frequent, but seems to revert to happening every 7 or 8 times I start the car.

I would be very interested in a fix that doesn't involve replacing the starter every 6 months.
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Old 01-05-2018, 03:09 PM
  #34  
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What about another shield bolted to the starter itself, like a heat shield.
OR this
​​​​​​​https://www.ebay.com/itm/Porsche-Hig...-/261157376960
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Old 01-05-2018, 09:30 PM
  #35  
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Over the past 6 1/2 years since I originally posted (), I have also had a recurrence a few times. My '87 does not have the reference sensor cutout in the bell housing. I have swapped starters with new rebuilt. I cleaned the 2 wire starter connection behind the brake booster (top). My current fix that has helped a slight starter kickback----now very seldom--is to use a midrange gas octane for every other fill up. Mixed with the remaining tank gas. ( I do not run premium). I have also increased the RPM to the 1000 mark at idle by use of the throttle body idle screw---not the throttle cable adjustment screw.
Another possibility of kickback is to let the car idle for a few seconds after a drive to clear the intake.
GL
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Old 01-06-2018, 03:07 PM
  #36  
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Problem is unshielded/sleeved timing sensor.
Resolution for crank position is worse when cranking and spark fires at wrong crank position, kicking back against engaged starter teeth.

Check that timing/reference sensors have the additional aluminum sleeve.

T
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Old 01-06-2018, 03:46 PM
  #37  
Tom M'Guinn
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Originally Posted by 951and944S View Post
Problem is unshielded/sleeved timing sensor.
Resolution for crank position is worse when cranking and spark fires at wrong crank position, kicking back against engaged starter teeth.

Check that timing/reference sensors have the additional aluminum sleeve.

T
Also, the strength (amplitude) of the speed/ref pulse is a function of speed, so keeping the battery on a tender and fully topped-off really seems to help, since the motor is cranking faster and the sensors are producing stronger pulses.
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Old 01-06-2018, 08:51 PM
  #38  
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Originally Posted by Tom M'Guinn View Post
Also, the strength (amplitude) of the speed/ref pulse is a function of speed, so keeping the battery on a tender and fully topped-off really seems to help, since the motor is cranking faster and the sensors are producing stronger pulses.
True.

Had a race car with this problem, starter kickback was so violent, I thought when the problem would arise, the bell housing would actually shear and leave us DNFd out of town and far from home.

I carry alot of parts, and have done a clutch on site at Sebring once but a bell housing swap was not something I wanted to do if it could be avoided.

Got the car home and experimented, installed aluminum sleeves around the sensors and never had the problem again.

Don't know how you could measure for it, but I don't think it's unreasonable to assume that a measurable current is present at the ring gear, transferred through the starter drive from the armature and/or the solenoid, through the fork and along the same path.

T
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Old 01-06-2018, 09:45 PM
  #39  
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Originally Posted by 951and944S View Post
True.

Don't know how you could measure for it, but I don't think it's unreasonable to assume that a measurable current is present at the ring gear, transferred through the starter drive from the armature and/or the solenoid, through the fork and along the same path.

T
Argues for big, short, clean ground straps in the area....
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Old 07-29-2018, 06:48 AM
  #40  
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Glad I found this thread, not so glad I actually need it :-)
I've been having some problems with backfire into the inlet on my 1987 944S.
First time was a couple of years ago. I tried to tart the car, heard a very loud bang (firecracker sound), and something fell to the floor. It appeared to be a small sort of lid (round, 63mm diameter, 4mm thickness) that was blown out of the bottom of the inlet collector. It was really scary, since I heard a loud bang, and some smoke was coming out form under the hood (oily smoke).
We inspected the cams, timing, ignition, etc. but couldn't fond anything wrong at all. Using some JB Weld, I glued the part back into the inlet collector, and the car started perfectly normal after that.
Afraid of getting the same blowout again, I always pushed the throttle in just a little while cranking, but this caused very hard starting from time to time (probably due to the fact that the idle switch wasn't pushed in?).
Ad so I stopped doing that. The car always started "at first click" ever since. Until a couple of days ago. Same thing. Loud bang. Something falling to the floor. Heavy sigh. Glue the thing back in, car starts again (now with quite a bit of hesitation, but I did push the throttle again a little bit, just to prevent this behavior again).
I'm not sure that I'm experiencing the same thing as you guys, it's not just a pinging, this is next level.
I'm wondering how starter interference could cause something like this? I will try to make some pictures of the sensor bracket that is installed on my car, and of the starter, to get an idea if this could be a possibility even.
Maybe I should pull the injectors, as someone on another forum already suggested (but I discarded that possibility too soon)? I have no idea how easy or hard it is to pull the injectors, but I'm getting tired of being afraid to start this wonderful car.
Once started, though, it runs perfectly at every rpm, and it pulls nicely (above 4K rpm, that is). I do have some sort of exhaust leak somewhere near the collector, I suspect, judging from the sound it makes. That makes it run a bit rich, if I'm right.
Thanks for any input,

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Old 07-29-2018, 07:30 AM
  #41  
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This is the best I could do with my camera to try and get a picture of the sensor that is now installed...
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