How to tell TDC???

macadamianut · #1 05-23-2010, 10:46 AM

When inspecting or changing the timing belt, how do you know TDC? There are two times when the crank index marks line up for every one revolution of the cams. What is the easiest way to know whether I am on the compression stroke? I can't get my finger all the way into the #1 plug hole.

Need to get this car back on the road before tomorrow morning, running properly or not.

I had the timing belt changed a year ago and I see that the tech lined up the marks on the belt with the crank and cam cover marks, but the cams are 180 out. If I rotate the crank 360, the cam pulleys index with marks and crank indexes, but the marks on the belt are 180 out. So, what would happen if the car was set up this way? I can't think that it would even start, so what gives here??

Thanks.

lhopp77 · #2 05-23-2010, 11:10 AM

All you need to worry about is whether the marks in the attached pic line up. It really doesn't make any difference about the belt marks as long as there are 53 cogs on each side of the crank center.

Also Note: Each of the cam sprockets as an UP ARROW that should be pointing UP when you align the alignment marks.

Lee

macadamianut · #3 05-23-2010, 12:20 PM

Thanks for the reply.

The trouble is, there are two times the crank is aligned with the mark on the case. One is the compression stroke (TDC) and two is the exhaust stroke. So it is possible to time the engine 180 degress out (plug firing on the exhaust stroke.) There has to be a difinitive way to note TDC, so when you set the cam pulleys to index with the cover, everything isn't in backwards so to speak.

ensteele · #4 05-23-2010, 12:38 PM

Are you replacing the belt, or did it go when you were driving it? If you are just replacing it, it pretty much stays were you had it and there isn't much adjustment that needs to be done. I have heard others state that as long as you get the marks in the same way as the how-to says, you are ok.

SoCal LS-L · #5 05-23-2010, 12:48 PM

Its not possible to have it 180' out..... as long as you align the notches to the corresponding marks, then engine is timed correctly. To be 180' off, you would have to purposely set the cam notches to the bottom directly across from the marks on the cover. The notch on the cam gear always corresponds to the compression stroke. You dont have to worry about messing up either (besides the time taken to redo it) since our H6 is non-interference. The crankshaft notch will always be on top when #1 is TDC..... the difference between exhaust stroke and compression stroke is the position of the cam...... if it were on the exhaust stroke the timing notch will be directly opposite the timing notch on the rear cover.

sowise · #6 05-23-2010, 01:08 PM

Earl I think he is asking because he has been having a stalling problem and Tom and others have recommended checking his timing and cams.

I think if you remove the plug from the #1 then reinstall it maybe 1-2 threads when you rotate the crank you should hear the air hissing from the spark plug threads. You want this on the compression side so when the air stops that should be TDC before it starts to suck air in. Also heard of using a 1/4 drive long extension placed loosely in the #1 plug hole. You will have to know when you are on the compression cycle of the rotation but as you rotate the crank you should see the extension rise. You will be at TDC when the extension stops rising or gets to max height before it starts to go down again. Just an FYI -If you are rotating clockwise and pass TDC you can rotate counter clockwise but you should always end the motion going clockwise again.

SoCal LS-L · #7 05-23-2010, 01:38 PM

Ill ask.... why go thru all that when the crank gear has a mark for TDC? There is only ONE TDC on the crank guys..... whether its the exhaust or compression stroke depends only on the cams!! Its idiot proof!

Its simple, align the marks on the crank and both cams... and BAM you are timed!!

macadamianut · #8 05-23-2010, 02:29 PM

Yep,

That makes sense. Corrected the belt alignment marks that were off by the tech's install. Everything is still indexed correctly. Is it normal to have a slight amount of movement in the tensioner pulley's bearing?

Thanks.

lhopp77 · #9 05-23-2010, 02:58 PM

If your car is a high mileage car it is best to replace the idlers and tensioner while doing the belt. Timing belt kits with idlers and tensioner are sold on Ebay for fairly reasonable prices. Think about water pump too.

Lee

ensteele · #10 05-23-2010, 03:03 PM

Quote:

Originally Posted by macadamianut

Corrected the belt alignment marks that were off by the tech's install.
Thanks.

Yep, you need to watch those darn Techs!

macadamianut · #11 05-23-2010, 04:54 PM

Crap,

Car's all back together.... Connected negative terminal on battery and it looked like the 4th of July! So I get in and sure enough, turn the key to the on position and nothing! Not even a dome light. No radio, idiot lights, nothing.

Touched the fusible link which immediately sizzled. WTF???

Help!!

sowise · #12 05-23-2010, 05:43 PM

Well hopefully you just fried some fuses and the fuseable link. Only way it could do that is if you had a direct short. Check main power cables before trying again. Check to the starter and check to the alternator. Make sure all your grounds are clean and secure. Hopefully you will find the problem that way. Otherwise you will need to get out he multimeter and do a continuity check from positive lead to gnd then go through disconnecting things until you it shows Open. Hopefully you will find it since it was shorted before you did the ignition, that should be a good indicator something is wrong direct to the battery.

macadamianut · #13 05-23-2010, 06:54 PM

Okay,

I think I found it. I pulled a super bonehead move and didn't notice that the crimp on the lower alt lead was touching the alternator housing.

Will replace fuseable link when I get it and try again.

Duhrrr!

sowise · #14 05-23-2010, 06:59 PM

You can verify your car works by making your own using a smaller gauge wire. Say your main wire is 12 awg then you could put in 18 awg or whatever. Too small and it won't carry the current you need and will heat up. Basically try to match the gage wire of the fuseable link. That should help you start it up make sure your alternator and voltage regulator are working and engine is running fine.

Glad you found it.

oab_au · #15 05-23-2010, 07:52 PM

Quote:

Originally Posted by macadamianut

When inspecting or changing the timing belt, how do you know TDC? There are two times when the crank index marks line up for every one revolution of the cams. What is the easiest way to know whether I am on the compression stroke? I can't get my finger all the way into the #1 plug hole.

Need to get this car back on the road before tomorrow morning, running properly or not.

I had the timing belt changed a year ago and I see that the tech lined up the marks on the belt with the crank and cam cover marks, but the cams are 180 out. If I rotate the crank 360, the cam pulleys index with marks and crank indexes, but the marks on the belt are 180 out. So, what would happen if the car was set up this way? I can't think that it would even start, so what gives here??

Thanks.

The easiest way to tell which cylinder, 1 or 2, is on the compression stroke, when the crank pulley is lined up with the TDC mark on the cover.
Pull both plugs out line the crank marks, then blow into the plug hole with a piece of hose. If you can just keep blowing, it is on the overlap TDC. If you can blow a pressure, it is the compression stroke, read to fire.

As for the belt marks.
Once the marks are lined up and the marks on the belt are lined, the position of the belt marks will move with each turn of the crank, does not matter.

Harvey.