What did I just do ?
Veteran Member
Joined: Jun 2013
Posts: 2,118
Likes: 1,374
From: Australia
I am curious to know if anything in fact broke.
To set timing and valve clearances one has to turn engine forward to have all 'plays' and 'chain sags' in the same position they would be when engine is running. While turning engine back seem like something we never (or rarely) do, I have issue accepting that turning engine back few degrees will "likely" break something. I think it is actually "unlikely".
To set timing and valve clearances one has to turn engine forward to have all 'plays' and 'chain sags' in the same position they would be when engine is running. While turning engine back seem like something we never (or rarely) do, I have issue accepting that turning engine back few degrees will "likely" break something. I think it is actually "unlikely".
There is not a lot of pressure on the tensioner on the slack side of the sprockets but backwards rotation will vastly increase the pressure on the tensioner as the chain pulls tight not to mention the mistiming that will cause between crank and cams.
Senior Member
Joined: Jan 2014
Posts: 429
Likes: 125
From: NJ, USA
Thank you, that explains.
I also understand that when engine always rotate in one direction all sliding parts develop 'fur' that does not like to be rubbed backwards. However, if I took 100 random XJS engines and turned them back let's say 5 degrees - how many would you expect would require repair after that?
Before reading this thread my guess would be "maybe 1".
I also understand that when engine always rotate in one direction all sliding parts develop 'fur' that does not like to be rubbed backwards. However, if I took 100 random XJS engines and turned them back let's say 5 degrees - how many would you expect would require repair after that?
Before reading this thread my guess would be "maybe 1".
Veteran Member
Joined: Jun 2013
Posts: 2,118
Likes: 1,374
From: Australia
Thank you, that explains.
I also understand that when engine always rotate in one direction all sliding parts develop 'fur' that does not like to be rubbed backwards. However, if I took 100 random XJS engines and turned them back let's say 5 degrees - how many would you expect would require repair after that?
Before reading this thread my guess would be "maybe 1".
I also understand that when engine always rotate in one direction all sliding parts develop 'fur' that does not like to be rubbed backwards. However, if I took 100 random XJS engines and turned them back let's say 5 degrees - how many would you expect would require repair after that?
Before reading this thread my guess would be "maybe 1".
The thing that would be the most annoying with such a breakage would be knowing that by turning that small amount backwards you are risking breaking something for no real gain. Any timing you set on any "driven" component after that backwards turning will be incorrect anyway.
Member
Joined: Mar 2017
Posts: 51
Likes: 22
From: Fountain Hills, AZ
I really feel for you. I think we have all been there, thinking we are doing something good and wham, you realize you just screwed something up. Wisdom and knowledge can be hard earned, all my best getting your car back in good order!
Senior Member
Joined: Nov 2015
Posts: 192
Likes: 42
From: Salisbury Heights South Australia
I have from time to time turned engines back a couple of degrees with no harm .This a long shot but is there any chance that the crankshaft bolt " cracked " open , they are usually extremely tight but worth checking. If it where my engine I would turn it over a couple of times by hand even if it meant removing plugs to lower compression and listen as well as feel to determine if it is ok .It may also be worth checking all belt driven items and see if any of those have a broken or cracked mount causing the belt to squeal and then its a punt to decide wether or not to hit the key or check the timing chains .