L20B cam timing

[JoelC]

Hey everyone. I’ve done a lot of searching and can’t seem to find the answer I’m looking for. I started out with doing a valve adjustment in my 79 620 as the top end was making a lot of noise. All rockers were at .018-.020 clearance. Tightened them to .010 on intake and .012 exhaust, engine hot. I’ve triple checked those figures to make sure it’s correct. Engine barely ran after that, back firing through the carb. Distributor had insane amount of timing retard, so set that back to 12* BTDC. Then set out to check cam timing. Made a chain wedge. Looked to be a tooth advanced. 

 

Retarded cam 1 tooth, better but still rough. One more, still rough, one more, won’t run. 70psi compression, I’m on dowel hole #2. Should mention it has an aftermarket timing chain set (from before I purchased) both lobes are up at TDC on compression stroke, though maybe a little on the retarded side, like 9:30 and 1:30 vs 10 and 2. There is no V notch on the cam sprocket for me to line up to the slot behind it. But I just set it to be centered in that closest window with both lobes up. No idea what’s going on now or where to turn next. I notice the cam sprocket has a second set of numbers (1,2,3) on the chain side, was not sure if that’s for the chain alignment or cam alignment? Any help would be appreciated!u

[datzenmike]

First you need a reliable TDC setting. There is a notch on the pulley on the crankshaft. It should be set to the 0 on the timing scale near the alternator, on the timing cover. This must be set by turning the crankshaft with a wrench in a clockwise direction. YOU MUST NOT BACK UP to zero. If you overshoot the mark back up a quarter turn and try again. As many times as needed to get it right. When the TDC is accurately set only then can you look at the cam timing. Normally the L20B is set on the #2 hole (middle) of the sprocket to the dowel on the cam. Bolted to the front of the cam is a thrust plate with a small horizontal etch mark. You can see the mark below just under the top bolt.

 

 

As you noted there should be a V or U shaped notch on the back side of the sprocket and when properly set to TDC, the V should be just under the ling or slightly to the right. just like the picture.

 

 

If to the left move the sprocket ONE dowel hole higher. Each dowel hole is about 4 degrees different from the ones on either side. Now you've moved it by advancing or retarding one tooth (which is 9 degrees) so it may not be possible to get it perfect. In this case you may have to move it a tooth back then check and move it by the dowel. The end result, no matter how you get it, is to have the V under or slightly to the right exactly like the picture above. This is a perfectly timed cam to the crankshaft IF the crankshaft is EXACTLY at TDC.

 

Take the sprocket off and very carefully cut notchs with a file

[datzenmike]

37 minutes ago, JoelC said:

Hey everyone. I’ve done a lot of searching and can’t seem to find the answer I’m looking for. I started out with doing a valve adjustment in my 79 620 as the top end was making a lot of noise. All rockers were at .018-.020 clearance. Tightened them to .010 on intake and .012 exhaust, engine hot. I’ve triple checked those figures to make sure it’s correct. Engine barely ran after that, back firing through the carb. Distributor had insane amount of timing retard, so set that back to 12* BTDC. Then set out to check cam timing.

 

Setting the valve lash should not do that, it should run better.

 

On a hot engine set to TDC and quickly adjust both valves on cylinder #1, the intake on cylinder #2, the exhaust on cylinder #3

TURN ENGINE ONE TURN, UP THE TDC and set the following valves...

exhaust on #2, the intake on #3 and both valves on #4...

 

Done, and fast enough so the engine does not cool down. Bumping the engine over for every valve is so time consuming, do it this way and you're done is 1/5 the time.  

 

70 PSI compression is very bad. What cylinder(s)??? Compression should be 150 or higher.

[JoelC]

My issue then is that this cam sprocket does not have a V or U marked on it anywhere...

[JoelC]

Alright. Advanced the cam 1 tooth, 9*, it’s running again (barely) and compression bumped up to 100psi. I guess I’m just gonna have to keep guessing with it since the cam sprocket does not have the mark to align with the slot on the cam plate. Or try and find a new cam sprocket I guess...

[datzenmike]

You want this ...

 

Doesn't matter how you achieve it. You have holes in the sprocket above the three numbers? Just get it as close as you can by eye.

 

Having the cam out by 2 teeth (18 degrees)  can lower the compression. 100 is still not good. Get the cam timed like the picture above.

[JoelC]

33 minutes ago, datzenmike said:

You want this ...

 

Doesn't matter how you achieve it. You have holes in the sprocket above the three numbers? Just get it as close as you can by eye.

 

Having the cam out by 2 teeth (18 degrees)  can lower the compression. 100 is still not good. Get the cam timed like the picture above.

Now it makes sense! Window above hole #2 (if dowel is in #2) need to be centered on slot. Thank you!

[wayno]

As I recall if you put that cam retainer on backwards there is no notch to set up the cam properly.

[datzenmike]

5 hours ago, JoelC said:

Hey everyone. I’ve done a lot of searching and can’t seem to find the answer I’m looking for. I started out with doing a valve adjustment in my 79 620 as the top end was making a lot of noise. All rockers were at .018-.020 clearance. Tightened them to .010 on intake and .012 exhaust, engine hot. I’ve triple checked those figures to make sure it’s correct. Engine barely ran after that, back firing through the carb. Distributor had insane amount of timing retard, so set that back to 12* BTDC. Then set out to check cam timing. Made a chain wedge. Looked to be a tooth advanced. 

 

Retarded cam 1 tooth, better but still rough. One more, still rough, one more, won’t run. 70psi compression, I’m on dowel hole #2. Should mention it has an aftermarket timing chain set (from before I purchased) both lobes are up at TDC on compression stroke, though maybe a little on the retarded side, like 9:30 and 1:30 vs 10 and 2. There is no V notch on the cam sprocket for me to line up to the slot behind it. But I just set it to be centered in that closest window with both lobes up. No idea what’s going on now or where to turn next. I notice the cam sprocket has a second set of numbers (1,2,3) on the chain side, was not sure if that’s for the chain alignment or cam alignment? Any help would be appreciated!u

 

I assumed he meant the etched line I pictured.

[banzai510(hainz)]

 

[banzai510(hainz)]

make sure the dist timming is near the middle of the adjustment otherwise your oil spindal is off. Most lile a oil pump was installed incorrectly butif this all of a sudden happen then its something else. if cranked all to one side to get 12deg then I would look into this.

 

there is a Melling Cloyes timming cam sprocket that has 3 holes and one wont be able to figure out the V notch timming as it don't have it. Then one has to use the timming bright links on chain. going by top dead center on the lower crank.

 

just watch my vid and hope this helps.

 

 

I had a tooth off but it wasn't that bad

 

 

was this running good before and what was done?!!!!!!!!!!!!!

[Stoffregen Motorsports]

16 hours ago, datzenmike said:

First you need a reliable TDC setting. There is a notch on the pulley on the crankshaft. It should be set to the 0 on the timing scale near the alternator, on the timing cover.

Best to verify TDC by removing the #1 spark plug and use a screwdriver on the top of the piston while you're bringing it to TDC. Once it "rocks over" check the timing mark. It should be just past the TDC mark. If not, then the timing pointer and/or crank pulley are wrong and a new TDC mark needs to be made.

 

Joel - do you have a dial indicator on an adjustable arm? If so, I can walk you through the "split overlap" method of setting cam timing. This way is stupid simple, but does require a dial indicator. This way also ensures proper cam timing while not requiring the degree wheel that engine builders use.

[datzenmike]

Stock cams are very forgiving with cam adjustment you can be out and never know it. Wear of sprockets and chain will 'add' length and this will have the effect of moving all the cam events later in relation to the crankshaft. Later opening of the exhaust and later closing of the intake. This slightly favors higher RPM and detracts from lower speed power and torque. It may be just noticeable. This is why there is a #3 dowel hole to take 4 degrees away.

[Rat-a-tat-Dat]

I remember the first time I replaced my head gasket. When it was physically necessary to set the timing on the cam, the presentable information I was reading seemed too confusing to grasp. My head just wasn't wrapping around the concept. I kept trying to rationalize and picture their meaning but failed miserably. It just seemed strange to start at number 2 on the sprocket instead of #1 first. Then the light bulb went off, and I kicked myself, when I removed the timing chain initially I had marked the cam sprocket with the block head surface. Selfishly thinking this was a quick way to reattach everything ( ha, ha ) and this premeditated assumption would help skip a few steps ( Doh! ). What Datzenmike previously pictured makes sense, but at that time my timing chain was stretched and I was unable to set the timing properly. Next lesson was to set sprocket timing on the number 3 hole and complete the repair until a new timing chain and related peripheral parts were acquired. 

The engine was running well at idle but had a hard time gaining speed and power, especially on up hill grades. Distributor was clocked all the way to one side also.

[datzenmike]

As long as you can get the little VEE just slightly to the right of the line above it... it doesn't matter what hole you are using. If you are already on #3 and can't get it, you are out of adjustment room.... then it's time for a new one.

[distributorguy]

Do you have a degree wheel?  Shoot for an INtake lobe centerline of 106-109.  Works well for most 4 cylinders.