Quick question: when you align the flats on the cams, is it possible for the timing to be off 180 degrees, ie that you should make another revolution on the main crank?

Back story: I bought an '99 XJ8 super cheap for the drivetrain and other parts that crossover as a parts car for my XK8. Passenger tensioner was blown. I wanted to determine whether the valves were toast before I pulled the motor, so I put in a tensioner from the XK8 replacement (only meant to be temporary), bought a new timing chain, aligned the flats on the cams and put the chain on. Cranked on the engine and it seems like it is majorly out of time.

Also, would being one tooth off cause it to be majorly out of time? I am pretty sure it was on but may take another look.

B

 

No. All of the stuff that cares what turn of the crank you are on is on the cams.

 

Did you position the crank with the locking tool?

 

Not sure what you mean Spark. And no Norri, i did not use any tools.

When I did the tensioner job on my XK8, I did the zip tie method and it worked great. The cam flat spots were parallel.

That is what I am asking about this job, can one blindly "time" the secondary cam to the main cam just by making sure that the flat spots are parallel???

When the tensioner blew, the chain jumped the sprocket. I bought a new chain and am trying to get the secondary cam back in time.

B

 

Hey Beep- Do yourself a favor and fashion a "tool" to set the crankshaft in position correctly so that you can be sure the cams are aligned correctly. It's an extra 2 minutes. It is worth the piece of mind alone.

 

I THINK (maybe wrong) an interference engine would blow up if 180° out since the exhaust valves would try to open with the piston at TDC rather than BDC.
You say 'timing's out' - does it run ?

 

Do you mean cam/valve timing or ignition/spark timing?

Turning the crank 360* will simply put the pistons back in the same positions. It's the CAMS that turn at half crank speed, not the pistons.

 

DSnyder, I think my eyeballs work pretty good in seeing they are aligned, I believe a cog off would be noticeable. However, I am open to the idea. Have you done so or can I search for it?

Steve, That is what i am asking. The hillbillies i bought it from said the car would start when i bought it (with the secondary chain off the pulley). I didnt want to chance it and changed the timing chain and put in a temporary tensioner. I cranked the car yesterday and while there was no loud noise, it wouldn't start acting like it was out of time. But it cranked fairly smooth.

B

 

Beep,

There's a locating pin that goes into the flex plate to hold the crank in the correct position when aligning the cam flats.
IIRC it goes into the same hole that the crank position sensor is in.
As you have had the chain off you need to go back to square one and set up from scratch.
There's plenty of threads with the details but this one shows some do it yourself tools.

 

There is NO WAY to time the engine without locking the crank in the right position. Do yourself a favor (and this poor Cat!), and read up on it. The "crank lock plug" can be homemade, but it's absolutely necessary. DO NOT keep cranking before the timing is confirmed!

 

OK, so as I understand it, I lock the crank with something similar to the attached .pdf. Once I have got the crank in the correct place, I should make sure that both pairs of cams are in perfect alignment using some flat object or tool. Correct?

My confusion still is: being one secondary cam (what is the cam the secondary timing chain attaches to?) is the only thing to go out of alignment due to the timing chain jumping the pulley, shouldn't I ONLY have to align the secondary cam with the main cam on the same side?

B

 

If you're saying that only one of the two cams on one head may/may not have slipped, and you're sure that it's companion is in the correct position, then I think, yes you could use it as a reference for alignment.

My A/R O/C personality would make use me use the tool anyway.

 

The exhaust cam is on the secondary chain. It's the lower one on the head. If the flats line up and the primary chain has not been disconnected I don't see how the timing could be off.
From what I have read here, the secondary chain was broken. This almost HAS to result in bent valves at the least.

 

Not necessarily true- I have bought two cars so far with broken chains and no bent valves.

 

Yes, just the exhaust cam on one side is out of alignment. I will try and realignn with some sort of flat piece.

That is what I am trying to determine, if the valves are bent. I got the whole car for $500, mainly for the tranny. I want to know if the motor is good or toast BEFORE I yank it out of the car.

Thanks everyone for helping me get to the bottom of this.

B

 

You can pull the exhaust cam out of the side that broke the chain and run compression tests- the intake cam is ostensibly still in time so with the exhaust cam out- no problem.

UNLESS the valves are severely bent- make sure to turn the crank by hand (only in the correct direction!) before running the compression tests.