I have previously posted about a knock that developed in my 140 motor recently. After checking the compression I couldn't get a reading on the #1 cylinder, so I tore into it tonight looking for a dropped valve or maybe something else. Now I'm more clueless than ever. The valves and head look fine and I even did a leak test from both the intake and exhaust sides to see and nothing came out. Next I pulled the jug and looked on the inside for any abnormal wear or damage and again came up with nothing. The piston looks good and the connecting rod feels tight on the crank. I pulled the #3 jug to compare and it feels like it has more play at the rod then #1 so I pulled #5 jug to compare and it has no "slop" just like #1. Now I'm really lost because it feels like the #3 rod bearing could be worn but it's the #1 cylinder with no compression.
If anyone has any ideas I would greatly appreciate any help at all, or if there's something else I can check please let me know otherwise I'll have to start trying to get a deal on a rebuild kit maybe.

Bummer.... this is were a video of it running would've really helped...

If the valves are good... it sure points to the #1 was adjusted way too far and the valve was hitting the piston...OODUDE suffered this...luckily he worked slower.. .ggg

Look at the top of #1... any marks?

If not.


I would put it back together and start over...

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I didn't see any marks but the head part on the #1 cylinder isn't black like the others so it definitely is something with that cylinder, I just can't figure out what.
Just to be sure, what kind of marks would I be looking for?

Crescent shape marks valve's edge hitting


Do you recall when dissasembling:


Were the rocker nuts on #1 way further down the 3 and 5?

Normal is approx. 3-4 threads showing above the nut

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what soes the head gasket and it's surface on the head look like? the cyl could have a crack along the long studs..pull the valves out of #1 and check for a cracked seat and carbon build-up that would stop the valve stem from going into the guide..

Tom Z,,Rochester NY

If it were a cracked seat would it still seal? When you say that the cylinder could have a crack along the studs are you talking about the jugs or the valve stems?
The surface on the head looks good and the valves still seal, that's why I don't know where to look from here. Could it be something with the crank?

I really doubt a cracked seat. Look at you rocker arms closely too. Inspect them where the ball is. I have seen a few crack there and it throws everything way off.

Texas YENKO Dude
YS-070
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Southeast of Disorder

Over-bore cylinders have been known to crack. Cam shafts that have been reground have been known to have a lobe go flat.
I assume you have made sue the valves on #1 are not stuck slightly open. I have seen valve seats that came lose but look fine until the valves are removed. in a couple cases they just fell out of the seat with the valve removed and did not show any real head dammage to the aluminum.
Also remove the lifters and see if one came apart. Have seen the retainer snap ring on lifters pop out.
Not common problems, but have happened and worth a check.

Corventure Dave

How about some pictures to see what you are talking about?

Here is all I have, a lifter ring/keeper that I found on concrete after a pushtube o-ring job. Removed lifter, reasembled and reinstalled.

Sam C. Saunders,Pt. Pleasant WV
68 500 cp 95 pg ash gold
66 Monza cp 110 4spd black
68 500 cp 95 3spd blue "DAIRY QUEEN CAR"

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All I really know at this point is that it doesn't seem to be the valves because they look good and there was no leaking when I put fluid in the intake and exhaust (I used brake cleaner and filled one side and let it sit, then repeated the process on the other side). The knock got louder as the rpm's went up, and there's no compression on the #1 cylinder. That's everything I know as of right now. I think what I'll do next is actually remove the motor so I can pull the top off and look down into it and see if that yields any more Info.

Could it be simply a bad lifter that's not pumping up and adjusted too tight to seat properly when running?

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Would a bad lifter cause a loud knock and no compression? I know some of these questions might seem dumb, but I'd rather ask a dumb question than do something dumb that costs me more time and $$$.
Thanks again for all the help and suggestions on things to check.

From what I understand a stuck lifter would give more of a clicking sound than a loud knock so I don't think that's it. I'm thinking it could be a stuck valve that's causing the 0 compression and the rod bearing on the #3 cylinder for the knock.
Does anyone know of a way to verify if a valve is stuck closed?

PLEASE STOP!!!!!


Your valve's rocker arm was most likely adjusted wrong...


Put it back together and we'll walk you thru adjusting them

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Just lay the head on the bench and using a rubber mallet tap each valvestem smartly and see if the valve moves..

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--you don't have to pull the engine to look at/work on the rod/piston/cyl 's : take the carbs off,top shroud,fan and unbolt the cover (the PCV tube covers one bolt,so take it off)..remove the sparkplugs from the left head and cover the holes w/shop rag so the engine (crankshaft) can be turned easier..to put the cyl back on #1 you'll need to install from the top to avoid breaking the rings on the rod-clearance notch..the con rods and caps should be marked on the top,and need to go back o the crank the same way (the bearing shell 'tangs' should be facing each other)..you can check the other rod bearings for play by holding each at the crank (thumb and finger) and turning the bolt on the HB back/forth a little (3/4" box-end)..let's get #1 back together and on the crank first,then deal with each problem- the 'knock',,and perceived 'no compression' on #1..

Tom Z,,Rochester NY

I tried adjusting the rockers before ever taking anything apart and that was not the knocking sound, or problem. I will see if I can get to the top of the engine to pull the fan and such but it is in a Fibertech buggy and there is a fiberglass "bed" area above the engine. I have thought about cutting more of it out, but have not yet. As of right now I only have a hole big enough to be able to check/ add oil, and for the center mounted carb which sticks out of the hole. i can see everything, but can't really get to everything as well as you guys can in the back of your cars.

Good to hear that you played with valve adjustment.... do you remember how many threads were showing above the nuts? Was it the same as all the others?


Sounds like pulling the engine is the way to go on this one.

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Check the top of the piston for a hole!