Go Back   986 Forum - for Porsche Boxster & Cayman Owners > Porsche Boxster & Cayman Forums > Performance and Technical chat

Reply
 
LinkBack Thread Tools Display Modes
Old 09-21-2019, 06:17 AM   #1
Registered User
 
Join Date: Jun 2018
Location: NJ
Posts: 24
Ran into problems replacing camshafts after pad replacement

Hi folks,

I have the engine out in my 2001 3.2S. Have replaced the cam pads on both sides. I started with bank 1 at TDC and removed the cam assembly, replaced pads and retime with a new chain and ensure the links lined up to the marks. Replaced the valve cover and checked rotation. Rotated the engine 720 degrees and looked fine. Next I moved on to bank 2 and removed the cam assembly. Realizing I didnt rotate the engine another 360, I went back to set bank 1, with bank 2 already out. Checked the alignment and all looked good. And held the cams down. Now when I try to rotate 720 degrees clockwise, at about 540, I feel resistance and no longer can turn the crank, spark plugs are all out. Bank 2 is out som must be something with my timing in bank 1. Am I hitting the valve and piston from the resistance I feel? Cyl 1 looks like the exhaust valve is open, cyl3 has the intake valve open. Cyl 2 is neutral.

What do I do now? Should I release the exhaust sprocket bolts, with he cam held down, allow the cam assembly to rotate back to a neutral position( no valves opened), set the engine back to TDC and retime bank 1 cams again?

Any advice appreciated. Better finding out if I did something wrong now with engine Out vs in the car and having a blow up on start.

Fchotika is offline   Reply With Quote
Old 09-21-2019, 07:37 AM   #2
Registered User
 
Join Date: Feb 2005
Location: It's a kind of magic.....
Posts: 5,429
First of all NEVER rotate one of these engines backwards, you will do a lot of damage if you do.

It sounds like you have missed on the cam timing, so you will need to very carefully remove the bank 2 cams. Then recheck bank one, reset the engine and start bank 2 over again.
__________________
Anything really new is invented only in one’s youth. Later, one becomes more experienced, more famous – and more stupid.” - Albert Einstein
JFP in PA is offline   Reply With Quote
Old 09-21-2019, 09:01 AM   #3
Who's askin'?
 
maytag's Avatar
 
Join Date: Mar 2018
Location: Utah
Posts: 2,217
Quote:
Originally Posted by JFP in PA View Post
First of all NEVER rotate one of these engines backwards, you will do a lot of damage if you do.

It sounds like you have missed on the cam timing, so you will need to very carefully remove the bank 2 cams. Then recheck bank one, reset the engine and start bank 2 over again.
I've heard y'all say this before, but I'll tell ya what: if there is so much slack in the timing chain arrangement that you can't turn these motors backwards (as y'all explained last time was the reason) then why don't we experience issues when you let off the throttle abruptly after a red-line pull?
I guess I don't understand the reasoning.

Explain for me?

Sent from my SM-G970U using Tapatalk
maytag is offline   Reply With Quote
Old 09-21-2019, 10:30 AM   #4
Registered User
 
Join Date: Feb 2005
Location: It's a kind of magic.....
Posts: 5,429
Quote:
Originally Posted by maytag View Post
I've heard y'all say this before, but I'll tell ya what: if there is so much slack in the timing chain arrangement that you can't turn these motors backwards (as y'all explained last time was the reason) then why don't we experience issues when you let off the throttle abruptly after a red-line pull?
I guess I don't understand the reasoning.

Explain for me?

Sent from my SM-G970U using Tapatalk
Because when the engine truly rotates backwards, the valve timing will result in instant piston to valve contact; even rotating by hand, the mechanical advantage is sufficient to bend valves. When you back off of WOT, the engine is still rotating clockwise; the only way to get it to rotate counter clockwise is by someone turning the crank backwards.
__________________
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 10:32 AM.
JFP in PA is offline   Reply With Quote
Old 09-21-2019, 01:00 PM   #5
Registered User
 
jaykay's Avatar
 
Join Date: Sep 2009
Location: toronto
Posts: 2,491
It may be valuable to state how is the clockwise direction is indicated on the accessory drive end of the engine. I don't remember seeing an arrow on the stock crank pulley way back when I pulled it off.

This direction will be opposite for 996s when using clockwise as referenced to the pilots view looking forward.

Any danger for those installing under drive pulleys or turning the engine over by hand?
__________________
00 986 S....with a few tweaks
jaykay is offline   Reply With Quote
Old 09-21-2019, 01:58 PM   #6
Who's askin'?
 
maytag's Avatar
 
Join Date: Mar 2018
Location: Utah
Posts: 2,217
Quote:
Originally Posted by JFP in PA View Post
Because when the engine truly rotates backwards, the valve timing will result in instant piston to valve contact; even rotating by hand, the mechanical advantage is sufficient to bend valves. When you back off of WOT, the engine is still rotating clockwise; the only way to get it to rotate counter clockwise is by someone turning the crank backwards.
So..... without arguing, I'm still gonna ask HOW?
I don't see any way that valve to piston contact can occur in one direction but not another. Those bits are, for all intents and purposes, fixed in relation to each other. I just don't see how the backwards rotation changes that?

Sent from my SM-G970U using Tapatalk
maytag is offline   Reply With Quote
Old 09-21-2019, 05:30 PM   #7
Who's askin'?
 
maytag's Avatar
 
Join Date: Mar 2018
Location: Utah
Posts: 2,217
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
maytag is offline   Reply With Quote
Old 09-21-2019, 05:39 PM   #8
Registered User
 
Join Date: Feb 2005
Location: It's a kind of magic.....
Posts: 5,429
Quote:
Originally Posted by maytag View Post
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
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 05:42 PM.
JFP in PA is offline   Reply With Quote
Old 09-21-2019, 05:49 PM   #9
Registered User
 
Join Date: Jun 2018
Location: NJ
Posts: 24
Ok. Thank you for the advice. I definitely did not turn the crank backwards. So I found that my cam hold down was too tight. Backed it off slightly and added oil to it allowed the crank to turn. Looks good so far with 3x 720 Deg rotations. Working in the ims and rms next.
Fchotika is offline   Reply With Quote
Old 09-21-2019, 05:54 PM   #10
Who's askin'?
 
maytag's Avatar
 
Join Date: Mar 2018
Location: Utah
Posts: 2,217
Quote:
Originally Posted by JFP in PA View Post
Yes, rotating the engine backwards, even by hand, leads to instant interference. Several people have discovered this the hard way.
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.

Sent from my SM-G970U using Tapatalk
maytag is offline   Reply With Quote
Old 09-21-2019, 06:06 PM   #11
Registered User
 
Join Date: Feb 2005
Location: It's a kind of magic.....
Posts: 5,429
Quote:
Originally Posted by maytag View Post
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.

Sent from my SM-G970U using Tapatalk
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
JFP in PA is offline   Reply With Quote
Old 09-21-2019, 06:21 PM   #12
Who's askin'?
 
maytag's Avatar
 
Join Date: Mar 2018
Location: Utah
Posts: 2,217
Quote:
Originally Posted by JFP in PA View Post
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.
Aaaaaahhhhhh.......
Ok..... I can buy that. All of it.
Thanks, JFP.

Sent from my SM-G970U using Tapatalk
maytag is offline   Reply With Quote
Old 09-22-2019, 08:29 AM   #13
1998 Boxster Silver/Red
 
Join Date: Sep 2017
Location: 92262
Posts: 2,061
Quote:
Originally Posted by maytag View Post
Aaaaaahhhhhh.......
Ok..... I can buy that. All of it.
Thanks, JFP.

Sent from my SM-G970U using Tapatalk
Yeah... JFP explains things in a manner that leaves me thinking, "Gotcha". I like knowing "why"... "how".

Cheers, MT.
__________________
1998 Porsche Boxster
1986 BMW 325es
2012 Ford Edge Sport

"Ignore the guilt, and take your turn"
Starter986 is offline   Reply With Quote
Old 09-22-2019, 12:37 PM   #14
Registered User
 
Join Date: Jun 2018
Location: NJ
Posts: 24
Great know how here. Thanks again.

Before I put back the transmission, can I test start the motor to see if it’s all running well? Flywheel on of course. That way if any running issues I don’t have to remove the trans again. I am doing this on a lift with an engine bar attached.
Fchotika is offline   Reply With Quote
Old 09-24-2019, 03:22 PM   #15
Registered User
 
Join Date: Sep 2016
Location: Stow, MA
Posts: 911
Garage
Quote:
Originally Posted by JFP in PA View Post
Because when the engine truly rotates backwards, the valve timing will result in instant piston to valve contact; even rotating by hand, the mechanical advantage is sufficient to bend valves. When you back off of WOT, the engine is still rotating clockwise; the only way to get it to rotate counter clockwise is by someone turning the crank backwards.
Or spinning 180 degrees without both feet in! Can happen on track and in autocross. Important to do full brake and full clutch immediately when you spin, otherwise the car will pull the engine backwards when you roll backwards after the 180.
__________________
2004 Boxster S Silver - FUNTOY
2002 Boxster Base Guardsy Red - FUNBOX
1987 Caterham Super 7 1700 Supersprint
2009 Mercedes Benz CLK 350 convertible
1941 Dodge Luxury Liner Coupe
Anker is offline   Reply With Quote
Old 09-24-2019, 04:37 PM   #16
Who's askin'?
 
maytag's Avatar
 
Join Date: Mar 2018
Location: Utah
Posts: 2,217
Quote:
Originally Posted by Anker View Post
Or spinning 180 degrees without both feet in! Can happen on track and in autocross. Important to do full brake and full clutch immediately when you spin, otherwise the car will pull the engine backwards when you roll backwards after the 180.
No, see, now you're off in lala land again, Haha. If it spins backwards under those conditions, then your tensioners are still pumped up, and no contact can occur. I've tested the theory, inadvertently.
I can tell you what WILL happen though. ;-)

Sent from my SM-G970U using Tapatalk
maytag is offline   Reply With Quote
Old 10-13-2019, 09:35 PM   #17
Who's askin'?
 
maytag's Avatar
 
Join Date: Mar 2018
Location: Utah
Posts: 2,217
So for the record;
3.2 motor from an '03 S, has been sitting on the floor in my garage for months. Hasn't run since June. No oil in the sump, been draining for months. So we can all assume no oil pressure in the hydraulic tensioners, right?

Motor turns either direction just fine. No contact, no noises, no resistance. Two full revolutions of the crank, each direction.

Now it's also fair to assume the hydraulic tappets are also "soft", so valves not going full lift. But I would assume if one is true, so is the other.

This is pretty definitive, to me.

Sent from my SM-G970U using Tapatalk
maytag is offline   Reply With Quote
Old 10-14-2019, 03:34 AM   #18
1202021
 
piper6909's Avatar
 
Join Date: Jan 2019
Location: PA
Posts: 1,247
I have no experience with timing on Porsche motors, but I do have some experience with Subarus. I've found that if a motor is out of time when you try to turn the crank by hand, if you do it slowly enough, the piston will hit the open valve and stop. Forwards or backwards. If you're careful and don't force it, no damage happens. Are Porsche valves THAT fragile? You'd think that if you turn backwards slowly and carefully enough, if you hit, you could hit the valves without damage.

Also, if you ARE off time in a Subaru, you can ALWAYS rotate the motor backwards enough to put all pistons back in the middle position. Subaru's timing marks are, in fact, set at the point where all pistons at the middle position, not TDC. I guess Porsches are not the same?
piper6909 is offline   Reply With Quote
Old 10-14-2019, 08:56 AM   #19
Registered User
 
Join Date: Jun 2018
Location: NJ
Posts: 24
Hi folks, got all my timing sorted and the cars runs well. Next problem to tackle is the engine to transmission mating. Tired for 4-5 days but still cannot get it to seat properly. Best I got it in was 1/4” gap. Just bought the 800lb HF jack with better adjusting head to try again. I took out the clutch plate and tried and it mated up no problem. But with the clutch plate it is been very difficult. Thus my alignment is likely off. My question: I have also read that you have to “draw” them in by two case bolts on each side greadully. Is this true? Or if I have them should just mate up flush right?
Fchotika is offline   Reply With Quote
Old 10-14-2019, 04:16 PM   #20
Registered User
 
Join Date: Sep 2018
Location: Laval QC
Posts: 180
Quote:
Originally Posted by Fchotika View Post
Hi folks, got all my timing sorted and the cars runs well. Next problem to tackle is the engine to transmission mating. Tired for 4-5 days but still cannot get it to seat properly. Best I got it in was 1/4” gap. Just bought the 800lb HF jack with better adjusting head to try again. I took out the clutch plate and tried and it mated up no problem. But with the clutch plate it is been very difficult. Thus my alignment is likely off. My question: I have also read that you have to “draw” them in by two case bolts on each side greadully. Is this true? Or if I have them should just mate up flush right?
So you were able to start the engine without the transmission? How did you support it?
On installing the transmission, I had similar problems (5-speed) and spent a lot of time fiddling around. My first problem was that my tranny jack was not quite high enough so I added a 2x6 between the jack and the transmission. Still it wouldn't slide all the way on, I think the gap was about a half inch. I measured everything and decided that at that distance the input shaft was already part way into the pilot bearing and the splines were in the clutch disk so I put a couple of bolts in and very gingerly tightened them, keeping the gap even, and got it all pulled together.
Good luck

__________________
Grant
Green 2000 Boxster 5-speed
1978 928 auto
1987 924S 5-speed (Sold)
Blue 2000 Boxster 5-speed (Sold)
elgyqc is offline   Reply With Quote
Reply


Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On
Trackbacks are On
Pingbacks are On
Refbacks are On




All times are GMT -8. The time now is 07:55 AM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2020, vBulletin Solutions, Inc.
Content Relevant URLs by vBSEO 3.6.0
Copyright 2018 Pelican Parts, LLC - Posts may be archived for display on the Pelican Parts Website -    DMCA Registered Agent Contact Page