Cam Chain Tensioner Mystery...

[rossiz]

so after replacing the head and futzing endlessly with the timing chain, i finally got her running. went in to do a valve lash adjust after ~600 miles on the new cam and discovered my cam chain was quite slack. while rotating the cam by the bosses i felt it turn a few degrees as the slack picked up in each direction.

when i replaced the head, the chain was super tight - so much so that i had to lever the cam sprocket on with a big wrench. it seemed too tight to me, but everything i read stated "zero slack" and that's what it was. the first startup turned over verrrry slowly for a few revolutions, then something clicked and the engine spun free and started. i figured the tensioner was clicking into position or seating itself after being displaced.

alarmed by the amount of slack i was now seeing, i got my little endoscope cam out and went into the abyss to see what the chain tensioner was doing, and i found it was.... completely missing!!! looks like it got sucked into the hole and i have no idea what to do now. oddly, i couldn't see any parts lying around down there, but they could be hidden in a cavity that i can't see.

the engine runs pretty well (not perfect, hence my valve check) and doesn't make any crazy noise like i would expect from a loose chain, but i am concerned to say the least. anyone experience this chain tensioner vanishing act??

a couple videos of the slack chain:

going in to look for the tensioner:

nothing there:

just a whole where the oil comes out:

am i reading these pics correctly? is the tensioner really rattling around in the bottom end? perhaps this might explain slightly lower oil pressure?

Edited August 22, 2014 by rossiz

[240260280z]

It must be down in the oil pan.

Great photos!

[Freez74]

Wow, what a handy tool!

[240260280z]

Neat to see the sprocket that drives the oil pump and distributor lurking below

[rossiz]

ok, i get it that the camera is cool and the pics are neat... but what about my L28???

[Diseazd]

Don't run it another second......pull the front cover and reinstall the tensioner plunger. You should be able to retreive the plunger with a magnet extender.

[siteunseen]

http://www.classiczcars.com/forums/engine-drivetrain-s30/50112-timing-chain-tensioner.html

[Captain Obvious]

am i reading these pics correctly? is the tensioner really rattling around in the bottom end? perhaps this might explain slightly lower oil pressure?

Yes, you are reading those pics correctly. The tensioner piston is no longer in the hole in which it is supposed to live. It somehow became dislodged and is probably swimming with the fishes down in the oil pan. And yes, in addition, since this is an unaccounted for unmetered source of oil flow, it could certainly account for slightly lower oil pressure.

Sorry you're going back in again. Just when things started sounding like you had reached the bottom of the curve? You don't get a break, do ya?

[EuroDat]

A bit of bad luck. Looks like it was dislodged when you did the head and popped out with the first startup. Probably that click sound you heard.

Here is a thread over on Ratsun Timing Chain Wedge - Engine - Ratsun Forums. Post #3 has a good photo of what has happened.

Chas

[S30Driver]

Sorry to hear "the valley of doom" has claimed your tensioner.

I know your are out of town this weekend, when you return, if you want any assistance, just let me know.

Many people make one - the tool pictured is 15 bucks from Amazon.

[Zed Head]

Might as well be the Debby Downer, but you would expect some damage to happen as it got levered out of the hole. Either to the tensioner parts or to the cylinder it sat in. Unless you're going to try to rig up a way to reinsert it from the top, with magnets and tape and skinny rods you'll be taking the front cover off, so you'll want to inspect the hole carefully. Should be able to poke around in the oil pan more easily then for the tensioner.

And I wonder if your timing chain didn't jump a tooth or two. In this case, it's easy to imagine. Might explain why it isn't running quite right.

There's a 79 ZX in the Arlington yard that you might be able to scavenge from. Row52 | 1979 Datsun 280Z

[rossiz]

so i've looked at the pictures of other chain tensioners popped out and squished up between the chain guide and the chain, and it baffles me how mine could have vanished - doesn't look like there's enough space for it to drop between it's housing and the crank gear, and the chain is going "upwards" (traveling clockwise) so it doesn't seem it would drag the tensioner down...

can i pull the oil pan without pulling the engine? looks like the front pan bolts are obscured by the front crossmember. i already have a new pan gasket (bought to do it "someday" to fix that nagging slow leak). i was hoping maybe with the oil pan off and the valve cover off i'll have access to the tensioner from both top & bottom and maybe i can put humpty together again???