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Old 12-30-2005, 05:14 PM
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success story - 'detonation' and 383

Hi guys,

I decided to post a success story here to let people see that not everything seems what it does and that it takes sometimes alternate approach to get things fixed.

Original engine combo: upgraded Vortec heads(take lift up to .525"), Edelbrock Performer RPM intake, 268XE cam, 383 stroker, 750 edel. carb, 190F t-stat, TH350, 3.73, HEI ignition, 67 Camaro.

Since I built that engine and installed it to replace a worn 350 in my 67, I have been having pinging (rattling) noises under load. I could 'play' with the throttle pedal and have these noises go away. Also since I didn't measure the quench, I was afraid that it also contributed to the problem. My CR was 10.4 (10.6) : 1. I tried running on a race gas, mixing it etc. The detonation was happening at random. One day the car would run great, then the next the noise would come back. The car had spent most of its time in the garage, because I feared destroying the engine. I needed to find a resolution to enjoy the ride.

I changed the spark plugs to the coldest ones, 190F t-stat to 170F, enriched the heck out of the carb, retarded the ignition, bought a new distributor, recurved it, installed an aluminum radiator, installed an oxygen sensor with a rich/lean gauge. Finally, I had had it and I bought a set of 487X heads with 74cc, replaced my 64cc Vortec heads and intake with a Weiand Stealth. I measured the deck height, quench, used the thinnest gasket. My CR now is 9.4:1. And guess what? The engine still detonated.

At this point I knew that it was a BS. I did some reading on this board, and some people commented on the flexplate cracks and loose torque converter bolts which could create those noises. Last week-end I got under the car, bumped the starter a few times to examine my flexplate and bolts. Everything looked good and tight. The only exception was the mini-starter gear being too close to the flexplate, 0.035". The instructions manual called for a clearance of 0.100+-0.045"! After shimming the starter, my clearance is now 0.105". Took the car for a test ride, and there is no more 'detonation'. I couldn't believe it. Such a simple, overlooked thing caused me a $500 damage, a few week-ends of swap time and a 6 month aggrevation! And I have a set of almost brand new Vortec heads and intake for sale since there is no way I am messing with this 383 again. The car has plenty of power.

Of course, after fixing it I did some reading again on this board using the correct search key words, and found a few posts by Edge who had had the same thing. I wish I could find and learn from his problems before I had tackled mine.

My big thanks go to all people who spent their time helping me out. This is a great board and I hope this post will help some poor soul out there :-)

Respectfully,
Denis
'67 Camaro RS

Key words for search: detonation , starter , ministarter , pinging , preignition , flexplate , flywheel, rattling

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Old 01-02-2006, 08:41 PM
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Wow! Thanks for getting back to the post on this problem. I never would have believed that a a starter clearance problem would cause such a headache! Just when you think you've heard it all, something like this happens. Hopefully more people will read your post and bank it in their memories for future reference! Later!
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Old 01-02-2006, 10:52 PM
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Just wandering did you seek second opinions by experienced gear heads before spending the $500?
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Old 01-02-2006, 11:11 PM
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It wouldn't happen to be a MCleod brand starter would it? Ive had that same problem with mine, and Edge helped me with that to.
Glad you figured it out


Brad
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Old 01-03-2006, 09:00 AM
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Hi guys,

Yes, I have heard and sought a lot of opinions. I actually had a couple of experienced mechanics drive with me in the car while I was making the car produce the rattling noises. People on this board healped me a lot too, of course, to them it is really hard to dignose the problem due to some many variables.

The model of my starter is 'Powermaster'. I am not sure if Proform makes them or not. Overall, its quality built is very high. However, whoever designed it probably knew something about the starter clearance issues otherwise he/she wouldn't have included the shims :-) (just kidding, since it is our job to make sure the starter clears everything).

Now, I hope to get my $500 back driving on 87 gas instead of 92. I am sure it wouldn't take that long on 10-11 mpg.

Regards,
Denis
'67 Camaro RS
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Old 01-03-2006, 10:41 AM
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You'd didn't know that flexplates aren't really all that round?

If you measure at one spot than you might be off by .100 at the opposite end.
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Old 01-03-2006, 11:04 AM
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Are you serius? No, I didn't know that.
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Old 01-03-2006, 04:29 PM
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Quote:
Originally Posted by johnsongrass1
You'd didn't know that flexplates aren't really all that round?

If you measure at one spot than you might be off by .100 at the opposite end.
Kudos to you Darom for giving us the skinny on your problem.

As far as flexplates go, they can be WAY out--both laterally ADD vertically (as measured when they are mounted on our Hines balancer). I have checked them both mounted on crankshafts and mounted on our flywheel/flexplate mandrel. Believe or not, some of the worse ones are brand name, SFI-approved pieces. .250" side-to-side wiggle and .125" run-out are not uncommon. I straighten out the side to side when I can.

Keep that in mind next time you try to figure out a noisy starter problem!

tom
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Old 01-03-2006, 04:46 PM
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Thanks, Tom. This is actually an eye-opening experience for me. When I got my balanced 383 parts back, I wish the machinist also wrote those flexplate off-set numbers along with usual piston weight in grams etc. My flexplate is a Pioneer piece that Powerhouse inludes in their 383 kits.

With best regards,
Denis
'67 Camaro RS
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Old 01-03-2006, 05:48 PM
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Again the experiances here though unrelated in a way to my problem may have just solved it, man I love this place. I'm having a simular problem with my 355, starter problems, noise problems, all steming from the flexplate area. I didn't know that the tolarances were that loose on the plates and I'm willing to bet now that is where all of my problems lie. Maybe now the hair pulling will stop before I run out, got to check that flexplate and starter clearance all the way around!
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