09-21-2019, 06:30 PM
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#1
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Who's askin'?
Join Date: Mar 2018
Location: Utah
Posts: 2,448
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Ok, I've been racking my brain, trying to imagine a scenario where this whole "turning it backwards breaks stuff" can be true.
Is there something about the cam chain tensioners that they "unwind" when the motor turns backwards? So the chains get slack and the timing changes that far?
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09-21-2019, 06:39 PM
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#2
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Registered User
Join Date: Feb 2005
Location: It's a kind of magic.....
Posts: 6,650
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Quote:
Originally Posted by maytag
Ok, I've been racking my brain, trying to imagine a scenario where this whole "turning it backwards breaks stuff" can be true.
Is there something about the cam chain tensioners that they "unwind" when the motor turns backwards? So the chains get slack and the timing changes that far?
Sent from my SM-G970U using Tapatalk
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Yes, rotating the engine backwards, even by hand, leads to instant interference. Several people have discovered this the hard way.
__________________
“Anything really new is invented only in one’s youth. Later, one becomes more experienced, more famous – and more stupid.” - Albert Einstein
Last edited by JFP in PA; 09-21-2019 at 06:42 PM.
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09-21-2019, 06:54 PM
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#3
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Who's askin'?
Join Date: Mar 2018
Location: Utah
Posts: 2,448
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Quote:
Originally Posted by JFP in PA
Yes, rotating the engine backwards, even by hand, leads to instant interference. Several people have discovered this the hard way.
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You didn't answer the why, or how. Do you not know?
While doing leakdown tests, I had zero problem turning the crank either direction to get each piston where I wanted it.
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09-21-2019, 07:06 PM
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#4
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Registered User
Join Date: Feb 2005
Location: It's a kind of magic.....
Posts: 6,650
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Quote:
Originally Posted by maytag
You didn't answer the why, or how. Do you not know?
While doing leakdown tests, I had zero problem turning the crank either direction to get each piston where I wanted it.
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With no oil pressure, all the hydraulic tensioners go dead, the chains go slack and there is enough slop to make the cam drive the equivalent of a couple of teeth out, which leads to contact. Some people seem to get away with it, probably because their hydraulic tensioners did not completely bleed down, or they were doing it on a five chain engine. It is worse on three chain engines than on five chain, probably because of the short chain between the cams holding everything more in time.
__________________
“Anything really new is invented only in one’s youth. Later, one becomes more experienced, more famous – and more stupid.” - Albert Einstein
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09-21-2019, 07:21 PM
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#5
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Who's askin'?
Join Date: Mar 2018
Location: Utah
Posts: 2,448
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Quote:
Originally Posted by JFP in PA
With no oil pressure, all the hydraulic tensioners go dead, the chains go slack and there is enough slop to make the cam drive the equivalent of a couple of teeth out, which leads to contact. Some people seem to get away with it, probably because their hydraulic tensioners did not completely bleed down, or they were doing it on a five chain engine. It is worse on three chain engines than on five chain, probably because of the short chain between the cams holding everything more in time.
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Aaaaaahhhhhh.......
Ok..... I can buy that. All of it.
Thanks, JFP.
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09-22-2019, 09:29 AM
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#6
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1998 Boxster Silver/Red
Join Date: Sep 2017
Location: 92262
Posts: 3,095
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Quote:
Originally Posted by maytag
Aaaaaahhhhhh.......
Ok..... I can buy that. All of it.
Thanks, JFP.
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Yeah... JFP explains things in a manner that leaves me thinking, "Gotcha". I like knowing "why"... "how".
Cheers, MT.
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1998 Porsche Boxster
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