Motor won’t turn over – any suggestions?
 

Hi all, searching for some technical help.

I just bought a 1999 Boxster – manual with 86k and the motor won’t turn over. With a breaker bar, the engine will spin ~ 90 degrees and then locks. It will move 90 degrees counter clockwise and then 90 degrees clockwise. Cannot complete a revolution.

Diagnosis:
Oil filter is clean. Oil pan had a very very small piece of the guide.
No damage to the plugs – & they look good.
Dropped the motor and pulled the rocker covers off, and everything appears be clean and good.
Used a borescope and wasn’t able to see anything in the cylinders.

I don’t believe it’s an IMS issue as I would expect to see some carnage. It feels like it may have jumped a tooth?

Next step will be to pull the cams to see if it will turn over with the cams out.

Has anyone seen this before?

Appreciate any advice on what to check next.

Thanks,
Philo

did you verify base cam timing ?? sounds like a bent valve. even a tooth wont lock it in most cases.. you should be able to look at the ends of the intake cams and see where the slots are pointing , will give you a general idea how far out you are. At TDC one points in one points out if i remember correctly. even if you cant get to TDC you should have an idea if its way out

Thanks, it won't spin to TDC.

looks like I need to take the cams out as a next step, but I won't have a reference for timing.

You can always retime it. Not all that complicated IMHO.
Iceman has the right idea... you should be able to see if the cams are way off time.
Otherwise, I would loosen the sprockets on the end of the exhaust cams, effectively isolating the cams from the crankshaft. Turn the camshafts so that no lobes are pushing on valves... The engine should turn unless a valve is sticking into a cylinder or something is jammed in the valve chain system or in and around the crankshaft. If it turns, retime the camshafts one side at a time.
If you remove the cams while lobes are pushing on valves the camshaft will lift and that can be bad...
This should work... unless I have forgotten something.

Thanks Grant - appreciate the advice, will give that a shot on Saturday.

Loosen the bolts on the sprockets, and I am still unable to turn the motor over.

Any suggestions for a next step (s)?

should be great if you could look through the spark plug holes, to see if you have a valve in there that is keeping the piston to move freely.

I bought a mickey mouse boroscope online that plugs into your phone, but I have never use it..

i don't think there is any spot on either bank where no lobes are pushing on valves.. i guess OP will tell us.

There is... in this video at about the 3 min mark it is explained.
https://www.youtube.com/watch?v=xXfR60GAJd0&t=3s
If the engine is set properly there is no tension on the cams when the cam cover is removed.

Grant - thanks for the link to the video.

Here's where I'm at.
Took the cams out and found scoring in the journals. Looking at the valve train - nothing appears out of the ordinary.

My assumption, due to the scored cams on both banks and with the engine still locked up, this will cost too much in parts and machine work.

So I bought a used engine with a LN retrofit bearing, and am waiting for the AOS to arrive. Will install a new clutch + and then hopefully it will run.

I would like to further investigate why this motor failed, but with lack of space - I will rip into it at another time.

Here's a pic of the cam journals.

http://986forum.com/forums/uploads02...1743018684.jpg

im not sure why you think this .. it is minimized but not zero ... all he is showing is TDC for cylinder one .. has nothing to do with 2 or 3 . or tdc for 4 but 5 and 6 have valves out.

Ive done this job so i can tell you there isnt a spot where everything is tdc on the same bank with no valves open at all ..

the only reason there is no tension on the cover when it is removed its because you have to lock them down first .. it is NOT because where the valves are positioned.

Sorry but I disagree. On a four stroke engine the valves on each cylinder are closed half of the time, from the bottom of the intake stroke through the compression stroke to the bottom of the power stroke. So the cylinder doesn't have to be at TDC to have the valves closed. In fact on TDC of the exhaust stroke the exhaust valve(s) are closing and the intake valve(s) are opening. So as long as the three cylinders on a bank are between the start of the compression stroke and the end of the power stroke all valves are closed.
I have changed the tensioner pads on 3 engines, which doesn't make me and expert but permitted me to make the error of removing the cover when the engine was not properly aligned (in fact it was aligned for the opposite bank, not the one I was disassembling). When I took the cover off one of the camshafts rose about an inch at the end opposite the chain. When the engine is properly aligned the camshafts rise about a millimeter.

I had cam journal scoring on an engine... it is discussed here.
https://986forum.com/forums/performance-technical-chat/85802-scoring-camshaft-bearings.html

Thanks Grant, I wish mine looked like that.

With my replacement motor, I hope to have it running in a couple of weeks.