Johnson Outboard Compression Chart
Couple questions folks.i have a 1979 115 evinrude with compression numbers of 100, 100, 95 and 90. I am gonna run some seafoam or deep creep? Through and see what happens.i checked the compression on the 150 evinrude i got with the nice project boat i bought and the readings were 85, 80, 75 and 60.i am gonna take the plugs out, run cleaner through everything and see what happens. The motor set up for a while and they ran it last summer after a loooong period of sitting up. I ran it with gas mixed with mucho oil to help prevent damage to cylinders due to dry run.is there a site where i can get the compression specifications for my engines???? They dont adjust the heads or gaskets on the production line ( but I guess you have never been seen an outboard producton line) thats why many V4's had different comp on either bank especially on the higher compression engines like 115 and 140's. The heads are sand cast and different parts left to right.You will probably fnd the engine had the same difference in comps from new as many did as I have checked many new engines of that era.It was common for 10 to 15psi difference between banks.Even funniert to see a shady tree mechanic rebore, new pistons an rings and get the same difference after the rebuild as before.It happened many times.
Start by checking compression. If low compression the cylinder will not draw any or enough fuel to function. Also check the reeds if one or more is stuck they will prevent the fuel from making it to the cylinder. All else fails could very well be a carb issue.
Johnson Outboard Compression Chart Johnson 175 1998
The shady tree mechanic always trying to apply automotive knowledge to an outboard.never works.The 140's were the worst as they had the highest comp ratio. This caused rough idleing and one head to run cold so the fix was to measure to the deflector crown and then machine the difference off the head.It made them run much better thats why OMC recommeded it and would process a warantee claim for it.You have noticed outboard manufacturers dont usually publish compression pressures.If you have one low cylinder on a v6/v4 you have another problem as the rods and pistons beng the same part have far less chance of being different. 60psi sounds like a broken or stuck top ring to me so I would investigate that straight away.150 V6 had fairly low compression heads as they were meant to be a work horse engine with its 1' carbs. It made a nice engine.There you go.todays lesson for the shady tree machanics.Now do you want to know how to do a quick check of the rings in a cross flow?
They dont adjust the heads or gaskets on the production line ( but I guess you have never been seen an outboard producton line) thats why many V4's had different comp on either bank especially on the higher compression engines like 115 and 140's. The heads are sand cast and different parts left to right.You will probably fnd the engine had the same difference in comps from new as many did as I have checked many new engines of that era.It was common for 10 to 15psi difference between banks.Even funniert to see a shady tree mechanic rebore, new pistons an rings and get the same difference after the rebuild as before.It happened many timesThe 140's were the worst as they had the highest comp ratio.
This caused rough idleing and one head to run cold so the fix was to measure to the deflector crown and then machine the difference off the head.It made them run much better thats why OMC recommeded it and would process a warantee claim for it.If you have one low cylinder on a v6/v4 you have another problem as the rods and pistons beng the same part have far less chance fo being different.There you go.todays lesson for the shady tree machanics.Now do you want to know how to do a quick check of the rings in a cross flow? Click to expand. So you've been on a tour round an outboard motor factory and now you know everything.They DO adjust compressions/ clearances, (pistons on some engines protrude from the cylinder) with different coded gaskets. I dont know about cheap nasty throw away outboards but bigger engines do.Don't call people shaded tree mechanics without knowing what or to who you are talking you'lle get bitten.You have already burned any reputation you might have had by a ridiculous suggestion, but I guess it was'nt so ridiculous to you.You are not a mechanic -I know you are not.
Comments are closed.