ENFORCER24

just did a compression test on my engine
between 120-125 on all except one
#7 had a cross threaded spark plug
i very gently got the tester to threat in about a 1/4 of the way
and only got 110 out of it
my question is
#1 , the 1/4 inch or soo i loose on the threading of the compression tester , will it effect my reading?
#2 whats the safest way to rethread the spark plug hole
#3 if i truly have one cyl down 10 pounds will it effect perormance that much?
#4 why cant any test i run on my boat return perfect results?
the last question is just a debate , but it seems as tho whenever i get curious i seem to find a problem i wouldnt have known about before

thanks in advance guys , these forums have never let me down

P/S , its an 88 mercruiser 454 / 330 , bout 300 hours on it

articfriends

iTrader: (1)

Buy a thread chaser at the auto parts store,with iron heads you may be able to fix the threads IF someone hasn't forced a plug all the way in with it cross threaded,if they have then buy a helicoil kit or pay someone to do it. Next step would be to pefform a leakdown test,19 year old motor will probably be very high on the cylinder with 110 lbs,Smitty

ENFORCER24

the engine doesnt run badly , and doesnt useany oil at all
i put 5 quarts in the middle of last year right after i bought it , and 5 quarts came out on this years oil change
she gets on plane nice and accelerates to 60 without a whimper ,
curiousity killed the cat in this case
i'm pretty sure the threads are damaged all the way into the head , the spark plugs threads where all mangled
i have a lil red cap in the hole for the time being until i do sumthin about it (the threads)
how does a helicoil work ?

Griff

I would not worry much about the one cylinder being at 110. You are very close to being with the 10% of highest to lowest compression.

Info on helicoils.
http://www.hillcliff-tools.com/helicoil.html

Pwrbt33

iTrader: (2)

If you have to use a heli-coil just fill the cylinder up with shaving cream, this will keep any of the debris from going in the cylinders and getting caught in the rings. Then when you are done just finish running the motor up on the compression stroke and blow it out the plug hole.

Good Luck.

John

H2Xmark

the shaving cream trick works good, a lot of the old school tech's use it. fix the plug hole and maybe run anothercompression test, try to perform with a warm engine.

stevesxm

if you are going to run a tap into that hole, take off those two rockers so you don't clip a valve on the way in......and i wouldn't put a heli coil in a spark plug hole.... i would use a time-sert... they are solid 1 piece w/ a shoulder and make the head as new.

Griff

I agree, Time Sert would probably be a better solution.

http://www.timesert.com/

rush

Snapon makes a thread chaiser that works from the inside out for spark plugs that works good.