V4/V6 family opinions & questions

[johnyrude200]

Well its that time of year where Ive decided to start familiarizing myself with a new group of motors.

I was wondering what folks opinions are on these two groups of motors, and what are the years of compatible gearcases and evolutional changes during the production runs?

From some limited studying of parts books, it appears with the V4’s the 85-115 motors are the same less the carbs, and 120-140’s are the same. Any differences in the gearcases?

The V6’s seem to be the same between 150-175, and 185-225’s the same?

Are the trim units all the same between 60hp (3-cylinder) – 225hp motors?

Are the V4 & V6 gearcases the same?

Big question – what are some of the production ‘quirks’ to look out for with these two families?

[frankr]

Short answer to a complicated question: You have to realize that the V4 came out in 1958. and evolved from there. So, over the years there were a multitude of changes. In fact, nearly everything at some time was changed, but certainly not all at the same time. Yes, in some cases horsepower differences were simple, oftentimes bore size, etc.

[fleetwin]

OK, I will try to separate the engine families to two basic groups:
V4-V6 cross scavenged engines
V4-V6 loop scavenged engines
The V4-V6 cross scavenged engines have been around since 1958. They are fairly rugged, and forgiving when it comes to cylinder wear/scuffs/scores. Generally speaking, their systems are simpler, they idle well, and most troubles are easy to diagnose. Today’s fuels have caused some problems with piston coking/ring sticking though.
The V4-V6 loop scavenged engines were introduced in 1985, alongside the cross scavenged models. I was excited about these engines when they were introduced, but lost enthusiasm for them within a few years. These engines are definitely better on fuel than the cross scavenged models, but tend to lack mid range pulling power. Because they are loop scavenged, they are relatively intolerant to poor piston fit/scuffs/scores. The fuel systems on these engines are very complicated, over engineered, and tough to diagnose. Some of my complaints were improved over time, 1993 brought significant improvements for the V6 loop powerheads. Later fuel systems were improved making adjustments and servicing easier as well. These engines do have a relatively complex fuel recirculation system that must work correctly to maintain decent idle quality.
There were so many minute changes to the gearcases, it is tough to say whether gearcases will swap between the two engine families….
The power trim units were a bit more interchangeable though, but the V6 loop trim unit is unique to that engine. The later model "fastrak" trim units were somewhat more interchangeable.
A good way to introduce yourself to these engines is to start with the cross scavenged V4 engines from the mid 70s thru mid 80s…

[frankr]

Good write-up, fleetwin. If I may add 2c, Mag CD ignition came out in 1973 on the V4 motors (’72, I believe on the 50-65hp). It was light years better then the battery CD ignition that preceded it. Electric connections under the hood were simple terminal strips with screws. In-boat junction boxes were gone. Fuel systems were simple. Electric shift variants were gone. They were good, fairly simple motors. Then they ran smack into the gasoline shortage and the change to unleaded. That caused some problems, most of which we’ve forgotten by now. But (at least in this area) we had water pump problems bordering on disaster. Eventually, it was worked out with the new plastic pump replacements. Oh, and the early power trim that hung on the outside was a Goldberg affair, not so good. Later units with the power trim between the stern brackets was a whole lot better.

[fleetwin]

Like Frank says, stick with mag CD V4s. And, if you want V4s with power trim, stick with the great integral systems….These really were great engines, simple, rugged, and easy to service….

[johnyrude200]

Well the origin of my question is I picked up a 1988 140 V4 to put on a personal boat and am interested in learning as much as possible about oddball quirks seen in these and their relatives as I start working on it/them.

Appreciate all the help.

[amuller]

I’ve been learning about these of the early 70s vintage with the much help from people here. These are interesting motors but many people would say they should be avoided, that the sweet spot is in the later 1970s. This is probably so unless you enjoy tinkering and scrounging. But you are into a later period entirely. If I were looking for another I’d place high priority on power tilt/trim. These motors are too big and heavy to wrestle up and down manually, and being able to adjust trim under way is very desirable.

[fleetwin]

quote johnyrude200:

Well the origin of my question is I picked up a 1988 140 V4 to put on a personal boat and am interested in learning as much as possible about oddball quirks seen in these and their relatives as I start working on it/them.

Appreciate all the help.

OK, so you bought a 1988 140hp, which is a loop scavenged, 90 degree V4, I am assuming it is a 20" model, so it uses the standard V4 gearcase with a different shift rod. This engine uses the conventional integral PTT unit, which is very rugged. Like I say, these engines lack mid range power, so you will want to prop it out as close to 6000RPM as possible. I guess you will want to begin with the conventional stuff, check gear lube and compression. If all seems good, then go ahead and pull the gearcase down for a water pump job and to lube driveshaft splines. The engine has a 9 amp alternator with a water cooled regulator which is under the powerpack (black plastic cover under rear of flywheel). All the electrical connections are under that powerpack cover, and can be real tough to deal with/easy to pinch the wiring, when trying to connect everything with the flywheel still in place. This engine uses both the quikstart and SLOW systems, like on your 70hp. The engine also has the crazy dwell linkage like on your 70hp, but it is adjustable (that dumb looking black plastic knob on stbd side). This engine has four plastic carburetors behind that crazy big ol air box which is attached with many SS bolts. This airbox is an integral part of the air intake system, the engine won’t run as designed without the box, its insert, gasket, and all bolts in place. Each carburetor has two air bleeds, the top is the mid range air bleed, the bottom is the idle air bleed, there are no adjustable needle valves. Keep in mind that this engine induction feeds in an X pattern. In other words, the stbd carburetors feed the port cylinders and visa versa. These engines are very difficult to deal with when idle problems erupt, and they love to spit lean…Don’t even attempt to make any adjustments/assessments running on a flushette, the engine must be run on its boat in the water when trying to deal with idle issues. Trying to make adjustments while running on a flushette will probably cause the engine not to idle at all on the boat in the water. And again, the recirculation system should be checked, which will help idle quality.
These engines use thermostats and a water pressure control valve to control temperature. I’m assuming the original plumbing is still in place on your engine, with hoses running from one head to the other, than on to the water pressure valve on the stbd side. It can be tough to get these engines to heat up at idle with this system, and salt water adds even more problems. The thermostat system can be simplified by simply using parts from later model engines, which eliminates the water control valve, using a big spring behind the thermostat like other conventional OMC engines.
Find an OEM service manual for this engine, don’t try to use the generic fits all books, to avoid excess confusion…..

[johnyrude200]

Well, I just realized that the two motors I was hoping to combine into 1 have a wrinkle. One is a XL shaft with a stuck powerhead, the other is a regular longshaft with a good powerhead but no gearcase.

Is there any issue transplanting the longshaft powerhead to the XL stack?

Both are 1988 models.

[fleetwin]

Do you mean put the XL gearcase on the 20" stack? Or, do you mean putting the good powerhead on the XL stack? Well, the good powerhead will go right on the XL stack, no problem, provided both are actually 1988 models.
"I think" the bigger XL gearcase will fit on the 20" stack, the problem is you will have to change out the driveshaft/shift rod, which means disassembling the gearcase.
Like Dan says, these engines really only have two carburetor assemblies, maybe the way to think of it is the engine has two 2BBL carbs….

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