Johnson "70mod"

[Per]

Phill, Don't know why the OMC engine looks the way it does but one thing is for sure, when Aprilia speaks about low to midrange they probably mean what we consider top RPM for our OMC 56" engines.

[hupiveneilija]

Another block. What a work from factory

[filthy phill]

yes that is typical craftsmanship from omc, I think they had stevie wonder working for them lining up the sleeves.

obviously no quality control was working that day.

what year was this ? 1992/3 ?

it is not even close to being right ha ha

[hupiveneilija]

Little update. Ign timing 17*>19*. Also made spring change for cooling. After slowing down from wot stopped engine, little thisnthat and measured head surface temp ~74*c.
Plugs look really good. As picture show in earlyer post.

Have to do something on prop/gearing to bring revs down a bit.

[filthy phill]

57 knots = 65.59
if your running the srx with extra cup lets say its 24 pitch,, slip will be around 10% so that means revs are around 7,750.

so all looking good.

as long as you can get it to last a good amount of time it sounds perfect.

I would think if you go bigger prop you will suffer too much on the take off.

what is your goal / what exactly would be perfect for you ? top speed ? or general use /

will this be for racing or for fun ?

[hupiveneilija]

For fun. Now I think its most usable for 1or 2person onboard. I can get more speed out of it for changing taller prop but use with two might suffer, dont know yet. If it has enough power then wont. On to do list.

Should try 1mm headgasket instead of 1.5mm.

[filthy phill]

if you have 1mm gasket it would give more compression, but I think I would be happy how it is.

what is the pull away like ? if already good then leave it like it is, if you need more pull away then maybe the 1mm gasket ?

just remember the more it revs, the faster it will wear out.

need to know what the rpm is.

[filthy phill]

pulling apart all these powerheads, have you had problems with removing cylinder head bolts ?
do you use a ratchet with socket or a impact gun to take them out.

where did you get the different sizes of head gaskets ?

[hupiveneilija]

No problems, use ratchet&socket. Only 2 broken earth studs on exhaust/water cover.

Sierra is 1,5mm and 1mm is in a ProMarine gasketkit.

[LittleCharger]

No problems, use ratchet&socket. Only 2 broken earth studs on exhaust/water cover.

Sierra is 1,5mm and 1mm is in a ProMarine gasketkit.

WSM and BRP are both 1mm as well.

Put the big pitch on her and spin her up!