RPM operating range????

[OldMercsRule]

Hi Guys, I own a couple of 1969 Merc 1000s and I know the factory guidelines are 4800-5300 for WOT. The one 100 HP I currently run on one of my boats I propped for 5300 and it seems to run great at that RPM, and it comes out of the hole on an 18' Sabrecraft very nicely. Should I run it at a higher RPM like 5500-6000? The reason I ask: is my now dead 1250 had the same recommended RPM range, and I was told, (maybe incorrectly) to make sure to not over-rev due to lighter rods on the 1250 then the later 1350s 1150s 1400s and 1500s. I generally followed that advice and got great service: (18 years out of the 1250). I also have a 1978 1150, a 1979 115 and a 1981 115 that I tend to rev a little higher, (recomended range 5000-5500) and I don't feel at risk to sneek up to 6000 if I want to with the trim. The later models benifited from the later improvements (I think) and were a little lower compression then the mid 70s inlines, (I had a 1976 1500 that I had to put 140 pistons in to deal with the lousy fuel we get today). That engine seemed to like 5800-6000 as the "sweet spot", and the WOT range was 4800-6000. Please comment if you know about these old beauties that I love, (as I don't want to "lug" them). Thanks in advance for your thoughts. JR

 

[Laddies]

Re: RPM operating range????

It's better to run most I/line 6s a little higher on RPM, than lower. I cked my Mercury Manual and even though it calls for 4800 to 5300 for the standard 1000 engines it calls for 6200 to 6500 for the same model BP engines, that use the same crank,rods and bearings so I can't beleive 6000 will hurt your engine as long it's in good shape but I can write it in blood either 8) Bob

 

[OldMercsRule]

Re: RPM operating range????

Thanks Bob, sounds like the party who advised me about the 1250 was wrong as well? The 1969 1000 was the last, (and likely best of the 90 cu inch motors), so I will crank em up a little more, at least the one I already had (which is in very good shape). I still need to road test the 2nd 1000 (that I just bought on the cheap) to see what it needs to make it good to go. The 1250 was the first 99 cu incher so I'm fairly sure the rods were lighter then subsequent 99s. Thanks, I value your opinion. JR

 

[Texasmark]

Re: RPM operating range????

You just told us you have been successful running a 35 year old engine with no problems.....can't argue with that.

I had the '89 115 (99.6 or 99.4 or something like that) and I had it on a Ranger padded boat. I had 2 throttle settings: Idle and WOT which was 6000. Boat is still in use today and still runs 6000; no engine powertrain work has been performed on it.

One of the problems we all have is separating fact from fiction when we receive information. Also there are different circumstances surrounding each of us whereas what works for me may not work for you.

Mark

 

[OldMercsRule]

Re: RPM operating range????

Hey Mark, Exactly right. The 1250 was on a fairly heavy vintage 16ft designed origionally for a 60 HP, and the 1250 broke the transom and keel, (shocking: I know) prior to my acquisition of the boat, and the guy rebuilt it to resemble, (the strength of) the battleship "New Jersy", that is why she is still on the water today. The 1250 was way too much power unless I was pulling multiple skiers et al, so the 5300 red line was used when pulling and would scare me if I kept her to the wall with no weight in the boat. I did run her up in RPMs on a small 1968 Carlson I had the 1250 on to win races but generally 5300 is where she ran very nicely for a very long time. I have not run my non PT 1000 nearly as much, and the boat is a little larger (18' vintage Sabercraft) that my kids use for their wakeboarding, (they fill up bladders with water to cause a big wake) yuk:%, (from the standpoint of an old waterskiier who likes zero wake). I am replacing the blown up 1250 with the 1000 and if it is closer to the proper power for the hull I may prop it for 6000, (it will probably scare me as well as that boat does not like 45 MPH very much), and I am putting PT on the other 1000 on the Sabercraft so I won't be bashful about grabing RPMs on that one either. I never worried about the 1000 as much as the 1250 due to what I was told about that motor specifically, (which may have been wrong, but who cares now). I have always run my later model inlines higher in RPMs, but their WOT specs are higher then the old girls. Thanks for the post. JR

 

[emckelvy]

Re: RPM operating range????

Twenty years ago I had a '64 850-6 which I rebuilt into a 1000, with larger carbs & upgraded exhaust baffle. Had it on a '69 14' Fiberform V-hull and it was an excellent performer as you can well imagine. Went about 44 mph in slalom skiing trim, and one time my brother and I had it up to 50 on a dead calm day with an old 2-bladed, 23" pitch alum prop. Although I didn't have a tach on it, I'm quite sure the rev's were approaching 6000 if not more.

This motor withstood all the hard running and skiing we could dish out and begged for more. Years later talked to the next owner and he said it was still running strong. I reckon if she was gonna blow up she would've!

Also ran the tar out of a later M1000 I built for another boat. One day, unbeknownst to me, the locknut on the spark advance stop had loosened up and the screw backed out, giving the motor a ton of advance. I thought it was running particularly strong that day and was amazed at the purplish spark plug electrodes! Fortunately it didn't hurt it a bit, I expect one of the more highly-stressed 99 C.I. motors would've burnt a piston or 2.

The old 90 C.I.'s don't have the performance of the newer ones but on a fairly light hull, and propped right, they do very well and have that much-desired 'vintage' look.

'Course back in the Day we didn't care about vintage, we just wanted a good enough hole shot to Deep Water Start on one ski !!!!

One tip that I found worked well on these is, use a 2.3:1 gearbox from a 66 C.I. 4-cyl, be it an early 70's 650 or 800/850/etc. The 2.3 gearbox gives you a wider range of props to choose from and on smaller hulls (16' or so) allows you to stay in that propeller 'sweet spot' (17P to 21P) in which there's just a ton of excellent-performing aluminum & stainless inline props to choose from.

In fact, for a boat pushing a real heavy load, the 2.3:1 gearbox with a larger-diameter, low-pitched prop would do very nicely. You can even use it on the older motors with brass reverse-lockout cams, with slight mods to the shift shaft and lockout mechanism. Just a thought!

Enjoy your 'Stack'.................ed

 

[OldMercsRule]

Re: RPM operating range????

Hey Ed, Great read. I do love these old motors. It is still fairly easy to find 'em around the Puget Sound area, (as you probably know). They don't have all the alarms, whistles and bells of the newer engines, you have to mix your fuel, and they run on all 6 all the time, (keep it simple stupid). They have weak cooling and some well known fuel issues, (but that is what you keep your eye on since it is certianly no surprize). Ever since the Thunderbolt ignitions: 1967 and later (on the larger engines, [I don't like the point triggered Thunderbolts]), 1968 on the rest of 'em, if I can find an old girl that still runs and has even compression I'm tempted to collect 'em if the price is right. Maybe some day the Eco nuts will force me to destroy them, but until then I'm just going to rock on. The 1250 short shaft on the 1968 14 foot Carlson tunnel hull I had was a real thrill to hot rod, and Lord: did it have a hole shot on that light hull. JR

 

[JasonJ]

Re: RPM operating range????

It is my belief that the old inlines were, and still are, some of the best looking and performing outboards ever built. They were very light for the power they produced. I challenge anyone to find a 125 hp outboard that weighs 270 lbs built today...While I have had great success with omc, the old mercs are still my preference.

 

[OldMercsRule]

Re: RPM operating range????

Jason Totally 100% agree. They are also fairly simple. Love 'em. JR

 

[Texasmark]

Re: RPM operating range????

Jason, I just read in a '94 sales brochure that you can go down to a current (4 cyl) 100 hp and still be at 348#.....supports your point.

Mark