Compression testing the cylinders…..super low!
 

If you followed my posts at all, it’s a 454 bored and stroked and yields 10:1 compression approximately. The problem I’m having is I decided to test the cylinder compression before putting this in the boat. The compression on every single cylinder was between 0 and 15psi. I popped off the head covers, re-did the rockers and now the cylinders are consistent 30 psi one through eight, is this low because the rings haven’t been seated as it’s a brand new build? I was expecting the compression per cylinder to be upwards of around 150 psi.

forgot to mention, the crank is getting two full rotations as I’m testing.

Are you sure you are running the valves and setting the lash correctly ?

This is basically how I set lash

Ill ask a dumb question, are you testing compression by using the starter to crank the engine

Is this a new motor?
Are you making sure that your throttle is WFO so it's pulling air in unrestricted?
Another thing you can try is to spray a little WD40 into the cylinder to see if it goes up.

even if it is a new build, compression should be much higher ! something is not tight! did you do a leak down test to find where is the leak ?

it’s a new build. I’m cranking it by hand. I cleared all the noise out of the shop and did it again. I plugged the spark plug hole with my pinky finger. I feel the pressure start and then it backs off, it’s leaking somewhere. I looked at the valves. They aren’t bent.

didn’t do a leak down test. I’ll push compressed air through the spark plug hole and listen for noise…

oh and the carb is off, engine gets all the air it wants.

You cant do a compression test like you are doing it, you need piston speed and about 3 or 4 full cranks around with the starter and all the plugs out except the hole you're testing.

EDIT: I hope there's oil in the engine, you need to crank it with the starter to pump the lifters up

/facepalm

yes there is oil in it. Gonna rig up the starter to a jumper pack with a makeshift circuit tomorrow and seee what happens.

still probably a good thing I did it since initially I was having zero compression and now I’ve got 30 in all cylinders. Would have to pull the motor from the boat in order to get the valve covers off and redo all the rockers.

Question, did you prime the engine through the distributor hole ? I wanted to wish your wife the very best in a speedy recovery, cant imagine what you both are going through.

Thats the only way I know how to prime it with oil. Soak all the rods and oil pump in oil. spin the oil pump under the oil to pull oil through it, fill your oil filter and get a priming tool to pump the oil through the engine and up into the heads.

I think your compression will jump way up when you crank it with a starter motor, and all the plugs out. I once changed my gear reduction starter from a 3.75 ratio to a 4.1 or 4.2 ratio. I had the 468 BBC engine out of my drag car to do some work and checked the compression before I put it back into the car. It was only around 165 psi and it was usually closer to 195 psi? I didn't think it could be the starter but couldn't find anything else wrong, so I reinstalled the old 3.75:1 starter and to my surprise the compression jumped 25 - 30 psi due to the faster speed of the 3.75:1 starter.

And there is what show’s you the trick we used to use with ‘cranking compression’ rules in circle track way back when. Slower we could crank (ie less engine rpm) the lower the cranking compression was.

Heres a compression gauge question for you SB, what brand gauge do you use in your shop, Im going to smash our snapon one into pieces and throw it off a cliff and was wondering IF you used a Snap on and your experience with their FAWKING valve cores!

I never owned a snap on compression gauge but I also went through the gauge accuracy questions. I would borrow 1 or 2 gauges from friends and then test the same cylinder with my gauge and the other two. Found up to 20 psi difference. Took my gauge and the higher one and connected them to a welding bottle with the regulator set to a certain pressure and then checked both gauges at that pressure to determine what they read. Mine was off about 15 psi and my friends was off about 5 psi. Sometimes it is the seal on the threads of the compression gauge that cause leaks or even the valve.

snap on. Approx 20-25yrs old ? Maybe 30 ? And a cheap actron. 15-20yrs old ? Both read within several psi of each other.

Correct me if I am wrong, but…. I was always told NOT to crank a new engine until I was ready to start it. This was especially true if it had a flat tappet cam. The cranking will remove some of the assembly lube and could lead to premature wear. I have always done it this way and never had an issue but am I being overly cautious?

So I have had numerous compression gauges thru the years/ My Snap on on is the most ergonomic/durable with its rubber coated gauge with exception of the damn schraeder valve . BUT the ONLY schraeder valve that works in it is one thats super soft and it breaks the spring every other time we use it then it doesnt work at all. NOTHING we have bought locally works in it either, so its a snap on only valve, full blown BULL SH##! . I wondered if you've had problems with them springs on valve breaking

That sucks.
I did have one (15yrs ago ???) that the Schrader on the psi release button thingy broke. I had acquired it somehow, so i have no idea it’s vintage. I do remember it being fine for a year or two once i ended up with it.

Note: i maybe use a compression gauge 5-10 times a year ? Not often, that’s for sure.

I’m no SnapOn tool fan. Too much $$$ for my cheap ass. Lol. I have just a handful of there things….if that.

Its strange that if I stick a ac valve core, valve stem valve core, milton valve core in it, we cannot get a good reading at all, will read 50 to 75 lbs at best on a 150 lb engine. With this super spongy soft core they sell on the tool truck (2 for 10.99), it works perfect.

Whats the latest Bm