wondering if compression numbers on 1977 v4 115 johnson are acceptable

[crankbait cowboy]

did the compression test today on it as it had been sitting for years. i squirted a bit of fogging oil in the plug holes and also in the carbs first. the held then carbs wide open . my numbers are 95 on 3 cylinders and 85 on the other. wondering is this acceptable and worth moving on on this unit. also it is very cold here and after thinking about it , it seems that it did not crank over very fast. had good battery on it but thinking maybe bad cables or a dragging starter. my assumption is that this could affect my compression numbers. am i right or wrong, and thanks for any input anyone can give me.

 

[robert graham]

Re: wondering if compression numbers on 1977 v4 115 johnson are acceptable

Compression numbers sound pretty darn good, especially for a 36 year old motor....run some de-carb through motor and it may improve readings, but the motor should run fine, compression-wise. As far as cranking speed, check battery and all cables and connections....and that means take each one off, clean thoroughly, grease and tighten....the main battery cables may be corroded inside their rubber jackets...and need replacement....

 

[emdsapmgr]

Re: wondering if compression numbers on 1977 v4 115 johnson are acceptable

Original factory compressions on that engine would be in the 125+ range on each cyl. Yours are significantly below that. You may find that a "decarb" may raise the compression somewhat. Not a bad idea on an older engine. It will help idling and possible overall performance. The numbers are fairly close to each other, so that's the good news. If your cyl walls are not scuffed, you may get many years of service, but it will be down on hp. I'd want to pull the heads. Check the head gasket seal rings for any problems (then repl them.) If it was ever overheated those gaskets could be part of the compression problem. You can easily see any cyl wall scuffing. Check to be sure the rings are intact. Adding lube to the cyls is good on an engine that's been sitting. It may temporarily increase compression, the effect of which will decrease as the engine continues to spin.

Compression numbers sound pretty darn good, especially for a 36 year old motor....run some de-carb through motor and it may improve readings, but the motor should run fine, compression-wise. As far as cranking speed, check battery and all cables and connections....and that means take each one off, clean thoroughly, grease and tighten....the main battery cables may be corroded inside their rubber jackets...and need replacement....

 

[phillnjack2]

Re: wondering if compression numbers on 1977 v4 115 johnson are acceptable

With numbers that low you either have sticky rings or a worn out engine.
its no good anyone saying for an engine that old its ok as its not.
some engines have less use in 40 year than some do in just 1 year.
you wouldn't say its ok for a 2 year old engine so its not ok for this one.

I would try a drop of seafoam, or power tune etc to do a decarb to see if the numbers come up.
people saying take the heads off and have a look ??? now that is where the age comes into play.
if the engine has never been touched in its life then the chances are the head bolts will just snap due to being stuck in there so long.
would be nice to get them off, but just take it easy and make sure the heads are pretty warm before touching them with a spanner/socket.

and do make sure you check compression with warm engine and carbs fully open with normal fuel in the cylinders and safety cord off the remote so no sparks flying around.

also before condemning any engine make sure the compression testing guage is ok too

phill

 

[crankbait cowboy]

Re: wondering if compression numbers on 1977 v4 115 johnson are acceptable

got some mixed reviews it looks like. think i will wait for warmer weather. ( 20 below farenhiet here ) and start with getting it cranking better. ( battery cables and wiring, and maybe dragging starter ) have not had it running and plan is to see if it has acceptable compression before spending time and money on other things, so a warm compression test was'nt in my palns. is that neccesary?

 

[little.boat]

Re: wondering if compression numbers on 1977 v4 115 johnson are acceptable

With 95 compression on a engine that had been sitting a few year and slow cranking because of how cold it is I would say when it is warm compression checked you will have really good readings. Low 100's maybe 110-115. If your getting a good deal on it I'd say go for it.