Compression check done. now.. a p r o b l em

[freeman]

Hello.

i did a compression check and got 140 dry and 150 wet......except #4  it is 90/100.   ok well cant fix that with duck tape.

thing is i watched a couple videos on youtube on how to..didnt want to miss something as its the 1st time..1st comp guage.

I pull all the plugs out and check.......no pressure ....hmmm.. put the intake plugs in then..good idea.

did the comp check.    wrote it down. all done. put the exhaust plugs in.

i see the blue smoke burn off after start up.. did a test drive and it stumbles at mid acceleration..more at full throttle.

i got back home and cleaned all the plugs but they werent bad. theyre dry.   so driving it to my places it still stumbles.

I hate the hell outa that what could it be? do i have to dismantle the motor and clean all the parts? unhappy.

are the plugs ruined or just one or 2. 

did i ruin the #4 cylinder even more?

i feel like it needs new coils but prob not.

 

Id appreciate any ideas. thanks

 

[datzenmike]

140/150 is good enough. This was a warmed up engine?

 

The low cylinder....2 things to try....

 

Set the valve lash. I think it's 0.013" for all.

Re-torque the head bolts. Do this on a COLD engine. Loosen only one bolt at a time and right away torque to 60 ft. lbs. You can do in any order you like.

 

 

 

The only thing that may need cleaning/replacing, are the plugs. Make sure you have NGK BPR6ES intake and BPR5ES for the exhaust side. If in doubt replace the plug wires and the rotor but NEVER assume it's a coil. Replace only things that are proven defective because the stock parts are better quality that what you replace it with and you may put in a bad part, confounding everything.

[captain720]

Mike I think it's 0.012.

 

I have a video on you tube for the headbolts and valve lash.

[freeman]

I should of typed some history..i stress out when i mess up this truck..got in hurry to post.

i want to mention that i lost my email and passwords earlier and had to rejoin..did so as freeman. im also wayne  here in Vegas that i first joined a few months ago with problem with timing when i replaced the oil pump. (my problem was i switched I1 and I2 plug wires accidentally and thought oil pump/timing was off)

 

I did the head bolts and valves about 4k ago. just put in the blue ngk plug wires and new copper tip dist cap n rotor.

i just checked the coils with timing light and shows current flowing thru both to get that thought away.

also i put a mechanical oil guage in the past week also..no problems the truck still ran great.

 

i also bought a new timing chain set this week to replace when it needs it...or do just the tensioner first.

 

but after the comp check yesterday..an immediate  studder.   it has even backfired thru the carb on one acceleration.  im going to be getting on the highway soon for a 75 mph run to the bank 20 miles away so will see what happens.

but i now suspect the oil may have damaged a weak spot in the head gasket and its starting to get worse?

ill be back to report the 40 mile round trip on the highway. Thank you for the responses.

-wayne freeman.

[freeman]

then again there is a problem.. maybe i should retorque the head bolts before the trip. im sure the valve lash is still good..no rattles.

[freeman]

this is helping me to think..

Forgot to mention ive always used the correct ngk  plugs.

since theres a problem i dont want to get worse....i think ill start with buying some new plugs in case i fouled one. also seems like it could be a fouled plug.

replace 1 the test drive replace the second then test drive so i can know which one fouled if thats the problem.

 

 

i did measure the oil i put in the cylinders..1 teaspoon per cylinder..maybe i put too much in somehow..idk.

[DanielC]

"im sure the valve lash is still good..no rattles."

No rattles, means the valve clearance is too tight.  It means no clearance.  It means a valve is possibly being held open.

[racerx]

throttle open all the way? did you use a screw in type of checker or plug in?  Plug in is not that accurate could be off by 15 lbs. from my own experience.

[freeman]

I have to open the throttle on a carbed vehicle for compression check? thought that was newer vehicles.

i used a harbor freight..its a screw in type..was thorough.  ill retorque the head bolts tomorrow and check the valve lash n look around..see if something looks off.

 

i replaced the plugs today...no change.  just looking around i took the coil wire off the front coil and it had oil there..i cleaned it up and put the wire back..then checked the other coil it had a little less but there was oil. i thought i found the problem but still stumbling..new coils didnt fix it.

ill check the new dist cap n rotor now.

 

i even got my melling m111 hi flow oil pump today while at autozone..will wait to install that.

i bought a bunch of parts from another 720 months ago...ill put another distributor in tomorrow also and see if its that.  it seems like an electrical studder issue and not the carb n gas. i filled it up today between autuzone and the bank.  it studders in all gears up to 75 mph and only at half throttle or more.  its constant studdering at full throttle so cant go full throttle.

any ideas to check is appreciated.  

[datzenmike]

Oil won't harm anything.

[racerx]

Yes, throttle has to be wide open, even for carb engines. Not sure why you think for only newer cars. Yes, good idea to check valve lash.

[datzenmike]

Never noticed much difference myself. May take an extra turn to bring to full reading. Most compression reading are on a cold engine so if good enough I assume it will be even higher when warmed up. I just use it to ID a low cylinder.

 

Stumbling could be the noticeably low cylinder which isn't doing it's share of work. This could be a bad valve which is easier to fix than re-building it. The best way to ID a badly seated or damaged valve is a leak down test. This involves stetting the piston to TDC and introducing compressed air into the cylinder and monitoring how much or how fast it leaks out. If through worn out rings you will hear the escaping air through the oil fill hole in the valve cover. If from a bad intake valve the hissing will be heard through the carb, if exhaust you will hear out the exhaust pipe.

[freeman]

Good  to know thanks.  i hate a problem happening during improvement work  seems the problem could be from anything.

i still have to check the new dist cap n rotor

and today  will do valve lash.

then the head bolts.

then put in a different distributor..

i want to do another #4 cylinder check that has to wait..gotta go back to work.

 

then leak down test in a couple weeks

 

will post results. thank you.

[freeman]

no time..so did distributor replacement..   didnt fix it.   i know i have a good spare.   most difficult longer lasting test actually.

buying me a leakdown tester soon

prob just a leakdown test needed...

probably messed up something from not opening the throttle during compression test. by the time i get to the back 4th cyl... plenty of gas in there by now

.  i wonder if that could harm a 250,000 mile motor?  

 

it doesnt smoke and idles fine. 

 

i have set the valves each time while the motor was hot and at 12 as factory says. should i try 13 or 11  with it having high miles would it matter?.

i did the comp check while motor was hot..so next time when cold wide open throttle will start with cyl #4.

 

.i can tell  with new  cap. rotor. plugs. coils.  ngk plug wires....its hauls ass..tries.. but then mid to high rpms...studdering out.

 

id like a rebuilt motor.    too bad theres not a simple reliable bolt on turbo available.

 

i just discovered Velocity TV channel...covering hot rod shops in the US.. rebuilding  motors..body work.  built 4x4s n ratrod races n such. good stuff.   

[datzenmike]

Having the throttle part open prevents it making vacuum at cranking speed so very little gas is sucked in. I've done them open and closed and there wasn't much if any change, maybe take two more turns to reach maximum reading. Do this on a warm engine, a cold one will result in a lower reading.
 
Set the valves to what the factory recommends. Too loose makes noise, too tight and they don't cool properly. The valves collect heat and the only way they are cooled is from the air coming in and contact with the head when they are closed, so they need to be closed as much as they are allowed. A overly tight valve may not even close tightly causing a leak in compression and over heating. Exhaust valves are specially prone to this and can burn a path across the valve face and even crack.
 



This is extreme. Actually it takes very little damage to cause very poor sealing and running.

[freeman]

Heres what went wrong.....A couple things i guess added up to the mid to high rmp stumbling.

1.. I put my new blue ngk wires on just before the compression check and finally found that the exhaust coil wire going into the distrib wasnt making contact. There was normal  burn marks at the bottom of all dist top terminals except ex coil..(on my new $40 copper tip dist cap)

. (Because i put the old dist and wires on and that stopped the mid to high acceleration miss). 

2.  Before finding the above problem i had taken the carb off and noticed the broken plastic arm that connects to the vacuum pull off (the carb part with the 2-3" vac hose on it). fixed with plastic epoxy i had already.

 

 

And more info...before finding the above-

1.  I redid a comp check on #4 and now its like the others at 142 dry 152 wet......acurate// perfect report.. there all exactly 142 / 152.

2.  i checked valve lash and  there all perfect still on 12*  hot motor...(13 guage wont fit)

 

 

I know i stuffed that coil wire in there well..and checked that a couple times but...no..whayever..

i dont know why how this crap goes awry when i do some improvement..i hate it..    hate to report it.

but it rolls quickly now...   hard to just drive slow.

 

Thank you. see yall next time because i dont like computers n reading til i need help.