no blow in number

Richard/Ca

Richard/Ca

Senior Member
I just finish putting my 4 should say 3 banger back togather. I tested it before putting it in the car (good thing). I only have compression in 1,2,4 Cy #3 won't even break wind. The other three blow my finger out of the hole. So I took the head off covered # 3 with some hard plastic and then turned the engine over first it tryed to suck the plastic in then to blew it out. Seem like it is getting compression that way. ???? I did not put new rings in it.:confused:
 
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" So I took the head off covered # 3 with some hard plastic and then turned the engine over first it tryed to suck the plastic in then to blew it out"

I am not sure what this or the title mean. If the head is off surely you can see if a valve is sticking.

why not just lap the valves and check the mating surfaces for contact pattern if there is no outright sticking. very simple to do

If you did not ring it, then why was the head off.
 
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Unless you forgot to put the piston in, about the only thing that would result in zero compression is a valve that is not closing. Are you sure your valve lash is set correctly, i.e., the gap between the valve stem and the cam follower (tappet)? Do you have adjustable lifters?
 
maybe a little diag was in order before pulling the Head like a leak down test.
i guess what your saying is after pulling the head you sealed off #3 hole with a plastic bag draped over the block tightly.. thats a new test for me lol.
what work was done to the motor ? how did it run before ? i would take a close look at the valve train.
 
Actually he said he covered #3 with hard plastic, not a bag over the block. I interpret this to mean some flat piece of plastic over the cylinder. Not very precise, but hey, it provides information.
As noted if it is not the piston, it is the valve, or, possibly head gasket. While the head is off, see if the valve closes smoothly on hand cranking, then check your tappett clearance, not with the piston at top dead center, but with the cam lobes at bottom dead center. Adjusting the valves with the piston at TDC will give a false reading on the valve lash.
 
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Thank you 1930 Coupe and everyone else. I'll make and try the tool in the morning. And no it does not have adjustable lifters also all the values are opening ant closing but I will check the value lash again. Never heard it run before just pulled it down to replace all the gaskets. Shop vac good ides big job.:)
 
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The cam has not completed it rotation and is not on it's heel yet. The tappet has/may not have reached the bottom of it's travel. If you set the gap before the cam is on it's heel it will/can change when the cam reaches the bottom (heel) of it rotation.
 
At TDC, intake has been closed a long time already (140 degrees), and exhaust is not gonna open for another 140 degrees. (approx numbers many cams differ slightly but only slightly)
That is a full 280 degrees of valve inactivity out of 720 possible degrees. In fact, being at TDC splits the 280 degrees right in the middle, meaning the cam is on its heel.

At bottom dead center I guarantee either the intake or the exhaust is open.

If someone thinks this is wrong then they need to provide more detailed info.

I don't think there has ever been a recommendation by a manufacturer to set lash at anything other than TDC. If so, post a link to such a document.

Purdy, are you willing to jump in here? dave
 
At TDC, one or both valves will be open during overlap.
At TDC both valves will be closed during the compression cycle.
Every 4/ motor opens the exhaust upon piston rising in ex cycle then closes, upon which the intake will open as the piston heads back down.
With the very narrow amount of overlap in these cams it is easy to mistake the compression cycle as overlap. The easiest way to tell is to remove plugs and hold hand firmly over hole then crank by hand/wrench. You can tell when compression cycle is, you will feel the pressure building. At this TDC, you are ready to check valve lash.
You can also look at the lifter pushing up on valve, ex first then intake.

J
 
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"At TDC both valves will be closed during the compression cycle."

My point exactly. If you are going to be adjusting the valves you will have the side cover off and will be able to see all this happening.

What you have said is a far cry from the earlier advice we got to adjust lash at BDC
 
This method of "9" works because the lobes are directly opposite of the corresponding number.
The piston will not be at either TDC nor BDC if using max lift of lobe.

It has been my experience that it is easier to find the compression stroke, make the adjustment then advance to next in firing order. I have corrected some very good race cars over the years this way.

Do what works for you, after all, this is fun. Isn't it?

J
 
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Well I check all the values this morning with the shop-vac method.I laid a piece of of a shop towel on top of each value and put the shop vac to the exhaust or intake hole the 2 values on #3 suck the paper so bad I could see the outline of the values. the rest were great.So I guess I have value lapping to do. Might just change those 2 values also.
 
Richard/Ca said:
Well I check all the values this morning with the shop-vac method.I laid a piece of of a shop towel on top of each value and put the shop vac to the exhaust or intake hole the 2 values on #3 suck the paper so bad I could see the outline of the values. the rest were great.So I guess I have value lapping to do. Might just change those 2 values also.
Click to expand...

Richard/Ca said:
Thank you 1930 Coupe and everyone else. I'll make and try the tool in the morning. And no it does not have adjustable lifters also all the values are opening ant closing but I will check the value lash again. Never heard it run before just pulled it down to replace all the gaskets. Shop vac good ides big job.:)
Click to expand...

You have a job ahead of you without adjustable lifters.
 
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