78 620, L20B foreign matter in combustion chamber.

[Atikin9000]

What happened to that #1 piston? Was that from the broken valve?

Valve didn’t break, valve seat popped out, and it was on #3. It was just like that when I popped the head off.

[Atikin9000]

well on the topic of the #1 piston, how much piston damage is ok?

 

What are some of the draw backs from running it that way?

[wayno]

well on the topic of the #1 piston, how much piston damage is ok?

 

What are some of the draw backs from running it that way?

 

I would not worry about that myself, but maybe I am ignorant of stuff like that and the hypothetical  issues it could create.

[Crashtd420]

The only thing I would do is prep the damage on the piston face.... don't leave those sharp edges.... they could be come a preignition source.... use some painters tape on the block only expose where you need to prep... that will get grit and metal everywhere....

How deep is that on #1...'what does #3 look like....

And please this is my opinion and what I would do if in that situation....

If I am wrong please correct me....

[datzenmike]

The only thing I would do is prep the damage on the piston face.... don't leave those sharp edges.... they could be come a preignition source.... use some painters tape on the block only expose where you need to prep... that will get grit and metal everywhere....

 

This. Just use some sand paper to dull the edges.

[distributorguy]

Yes!  Knock down the high spots and smooth it out.  Since the pistons are soft, you could even scrape it smooth with a pocket knife.  Just don't leave metal standing proud that can attract carbon or attract undue heat.  

[Stoffregen Motorsports]

Pinging can ultimately be caused by any sharp edge like that because of the reason described above.

[racerx]

Yep...hot spots.

[banzai510(hainz)]

antiseize those intake exhaust bolts when done

[Atikin9000]

 

 

Did some more cleaning

 

And a picture of #3

[wayno]

That seat left you a lasting impression, something to remember.

[Atikin9000]

Is there a particular way the fuel pump eccentric washer guy needs to align withe cam sprocket?

 

 

 

Also any suggestion on setting the head to tdc before being reassembled to the block?

 

I set everything at tdc before the machine shop trip and I got the head back no longer at tdc lol. I was thinking of using the cam boss....maybe?

[datzenmike]

None at all it just has to make the pump arm go up and down.

 

Set the cam sprocket on the #2 hole, (loosely)  and rotate till the horizontal etch line on the cam thrust plate is just to the left of the Vee on the back of the sprocket. This will be close to TDC. Once together re-examine this and adjust if needed, but for most cases this will be close enough

 

Little late now but the cam and chain should also have been marked to get it back together on the same tooth. Again pull up the chain tight on the driver's side and put on, then check the etch mark to Vee position and move a tooth one way or the other and check again.

 

The Vee must be under and just slightly to the right of the little line above it. Nothing else matters. Get this relationship, and the cam is timed.

 

You will have to turn the engine clockwise up to and stop at TDC to remove all trace of slack on the tension side. If you over shoot, back up 1/4 turn and try again. Ten times if you have to. It must not be backed up to TDC only clockwise, or you will introduce slack into the tension side. Use the timing scale on the front cover for TDC.

 

 

I use vice grips on the two square lumps on the center of the L20B cam. Use the timing scale on the front cover for TDC mark.

[Atikin9000]

None at all it just has to make the pump arm go up and down.

 

Set the cam sprocket on the #2 hole, (loosely) and rotate till the horizontal etch line on the cam thrust plate is just to the left of the Vee on the back of the sprocket. This will be close to TDC. Once together re-examine this and adjust if needed, but for most cases this will be close enough

 

Little late now but the cam and chain should also have been marked to get it back together on the same tooth. Again pull up the chain tight on the driver's side and put on, then check the etch mark to Vee position and move a tooth one way or the other and check again.

 

The Vee must be under and just slightly to the right of the little line above it. Nothing else matters. Get this relationship, and the cam is timed.

 

You will have to turn the engine clockwise up to and stop at TDC to remove all trace of slack on the tension side. If you over shoot, back up 1/4 turn and try again. Ten times if you have to. It must not be backed up to TDC only clockwise, or you will introduce slack into the tension side. Use the timing scale on the front cover for TDC.

 

 

I use vice grips on the two square lumps on the center of the L20B cam. Use the timing scale on the front cover for TDC mark.

 

Bottom end is ready to go and is at 0 on the scale, gotta pop the distributor cap off and double check there. I marked the chain and I marked the cam sprocket but since the machine shop had in solution it was gone, also initially the truck was timed 30 degrees over with the v notch lined up befor pulled the head.

[wayno]

Turn the cam to TDC before you mount the head, as if you try to turn it after the head is on the block, the valves will hit the pistons.

[flatcat19]

Is the chain tensioner wedged? Or did it pop out when you remove head?

[Atikin9000]

Is the chain tensioner wedged? Or did it pop out when you remove head?

 

I’m missing these two johnnies too, timing cover bolts, and a lower manifold bolt.

 

Wondering if local hardware store will have something similar? Any suggestions for hardware?

 

[datzenmike]

Piston looks like at TDC to me not 30 over. 

 

Cam timed, both #1 valves will both be closed and #4 valves will be: intake just barely beginning to open and exhaust almost fully closed. There will be no problem this way. Carefully set the head in place. Make sure both dowels are in the block. Head should plop down into place. If head does not appear to seat properly stop and find out why, don't tighten the head bolts.

[Atikin9000]

Piston looks like at TDC to me not 30 over.

 

Cam timed, both #1 valves will both be closed and #4 valves will be: intake just barely beginning to open and exhaust almost fully closed. There will be no problem this way. Carefully set the head in place. Make sure both dowels are in the block. Head should plop down into place. If head does not appear to seat properly stop and find out why, don't tighten the head bolts.

 

Pistons are nowhere near TDC. Get a long stick that will fit the spark plug hole but can't fall in. You can watch it move as the piston comes up.

.

This is when I took the head off initially.

 

 

 

 

This is where the head was at when the bottom end was in the position in the above picture.

[wayno]

TDC is when #1 piston is all the way at the top, there is no other TDC.

The piston appears to be real close to TDC in this photo and this is where the piston has to be when you time the cam, the piston has to be as high in the cylinder as it can get.

[distributorguy]

That piston is way down the hole.  10mm?  Considering TDC is between .015-.020" down the hole.  That's at least 30-50 degrees off TDC.  

If reusing an old chain, you may want to set it up on #3.  That's what 2 and 3 are for - adjustments for stretched timing chains.  

[datzenmike]

On wrong tooth. Moving to #3 only takes away about 4 degrees.

[racerx]

V notch should be on the slot? Seems off

[datzenmike]

Should be below and just slightly to the right. Moving one hole to the next higher number removes about 4 degrees and moves the Vee about the width if that horizontal line to the left. Arguably that one could go to the left. I wouldn't worry about it.

[Stoffregen Motorsports]

One big question is always the timing pointer. How many of you guys actually verify TDC before installing the head? It's not hard to do.

 

The reason I always bring this up is because over time, the sloppy and flimsy timing pointers can be bent, cracked, or just plain wrong.

 

With the engine before TDC, bring the piston up slowly and feel it rock over with your hand on the crank pulley. As it starts to travel back down the bore, back it up and zero in on TDC, then check it against the pointer. Once you verify it, mark the tip of the pointer and the notch in the pulley with paint.