TDC

[cabinfever]

As some of you know, I am replacing a head gasket on my F134. I want to check the intake valve lash before I start up the jeep after the head is on.

I went under the jeep to look at the timing marks and there aren't any! It appears that there was a timing tab on the crankshaft cover but it was either busted off or cut off. (Don't ask me how I am going to time this engine when it needs it!)

At any rate, I want to leave the #1 piston at TDC before I replace the head. Then once every thing is back together, I can start checking valve lash with #1.

My question is, how do I tell when #1 is at TDC by looking at the operation of the exhaust valves? I know I could look at the rotor position, but it's a hassle opening my distributor with this heater core sitting on top of it.

Thanks

[wesk]

A better question that would be more appropriate is how does Steve solve his problem permanently?????


Fix the missing mark!!!!!


4 stroke engine!!!!

The piston rolls down on the power stroke then the exhaust opens for the exhaust stroke and then closes as the intake opens for the intake stroke, then the next stroke up is compression.

You turn the engine over until the #1 intake starts to close. Then slow down and observe the #1 piston on it's way up. Put a dial indicator across the #1 bore and when upward motion stops make the notch or V or drilled hole in the crank pulley align with a tab that says TDC. Now put a degree wheel on the crank pulley and rotate the crank backwards 5 degrees. If you don't have a mark that says 5 Deg's yet then make one.

Voila!

You can save all the marking and just call John Bizal and have him send you a new timing tab. The CJ5 part No. is 906113.

[cabinfever]

Good advice, Wes. Thanks.

I can do exactly as you recommended, but shouldn't I be observing the upward movement of the #1 piston and making my marks on the crankshaft cover as the #1 piston moves upward on its compression stroke to find TDC?

[wesk]

Right, My Bad!

OK I corrected the previous post.

Don't waste your time playing with various marks on the cover. Just put that new timing tab from John on there first. Then get the #1 piston at true TDC using a dial indicator to confirm it exactly. One thought here. Due to the engineering marvel call the reciprocating engine there is a 2 or 3 degree flat spot at TDC where as the piston gets ready to switch to down travel the crank moves the 2 or 3 degrees while the piston sits still and then the piston starts on the way down. This is why I use the dial indicator. The instant the up motion stops I make a pair of reference marks on the pulley & cover with a sharpie. Then as I continue very slowly the rotation of the crank the instant my dial indicator starts moving I stop and make the second pair of reference marks on the pulley and cover with a sharpie. Your true TDC is halfway between these two marks. Make a red sharpie mark halfway and that red mark should align with the TDC on the new tab if no one has substituted any parts on your engine IE pulleys. If the new red mark does not align then simply make a V or notch in the edge of the pulley that is in line with the TDC mark on your tab. Voila, you are done and never have to address this issue again.

[cabinfever]

A little good news. There actually is a timing tab on the crackshaft cover.

When I looked from underneath the vehicle, it didn't look quite right. After seeing your photo above, I took a second look and sure enough it was there. DOH!

[4x4M38]

Thanks Wes. That's very clear and concise.

[wesk]

Steve,

Since your is significantly bent & wrinkled I would check it anyway while the head is off. You may need to just tweak it a wee bit or it may be 5 or 6 degrees off.

[cabinfever]

Roger that. Thanks, Wes, for walking me through this.