adjust engine mount

[Navgunner]

I have been reading other posts and think I may have come across a solution. I am running a 1973 135HP Evinrude Model # 135383M on a 17 ft glasstron. I get about 5000 to 5200 rpm WOT. I cannot get a slalom skier up, it will pop a 2 ski right up. Was considering trying a different pitched prop, but read that adjusting engine mount might do the trick. Mine is mounted as low as it will go. First is this a possible fix? And second, what is this sucker gonna weigh in at? Could one or two guys lift it up while another re-bolted the top bolts? Thanks for any feedback you could provide.

 

[OBJ]

Re: adjust engine mount

Think you'll want to get the anti-cavitation plate at least one inch above the keel of the boat. No....I wouldn't want to try and lift that sucker....a shop hoist would be nice. And you'll want to get the engine WOT rpms closer to 6k. These are all basic things that will help. Dhadley could probably help more.

 

[MarkHPCA]

Re: adjust engine mount

You can also use the trailer to help jack the motor up. Crank the trailer jack so the front of the trailer is as low as possible then put some blocks under the motor skeg. Now have someone steady the motor and loosen the mounting bolts. The bottom ones should be in the slotted part of the mounting bracket so you can carefully remove the top two bolts and, with the bottom ones loose, crank the trailer jack so the front comes up. This will allow the motor to lift in relation to the boat. Align to the new top holes and put back the bolts. Remeber to seal the holes well and tighten the bolts after.

 

[OBJ]

Re: adjust engine mount

Ahhhhh, inovation....I like it!

 

[Boilermaker]

Re: adjust engine mount

How much will adjusting the X-dimention affect the hole-shot??? I can see the high drag of a lower engine mounting effecting mid & upper RPM, but does it really effect his hole-shot alot???<br />Just askin'.<br /><br />I know a lot of folks run 2 different props, one for crusing & one for sking.<br />

 

[umblecumbuz]

Re: adjust engine mount

MarkHPCA's method is easy, and it works.It needs two people.<br /><br />Before I discovered that, I used to put an ordinary hydraulic jack on the skeg, with a block of softwood between. <br /><br />This method had two advantages. First, I could do it on my own. Second, I could sit by the jack, loosen the bolts and fiddle with heights while tightening at exactly the right moment.<br /><br />It really is that easy!

 

[Navgunner]

Re: adjust engine mount

Thanks for the advice guys, I am definitly gonna give it a shot. In fact now I really have issues. I had to replace my prop which was a 13x19 and the new one is 14x19 cupped. I have really lost rpms now! I think I topped out at 4700. Will the increased diameter cause this? or am I fighting multiple problems here and just not realizing it.

 

[Boilermaker]

Re: adjust engine mount

I have been fighting a similar problem, Navgunner.<br />The same thing happened to me when I switched from my old style 13x19 OMC prop (spun the hub) to a new 14x19 Johnson prop. The new prop was a different shape and had cupped design. KILLED my holeshot & upper RPMs.<br />I found I had to drop to a 14x17 Johnson prop. That got me most of my holeshot & rpms back..Its the cupping! <br />Then I got a Stiletto 13x17 S.S. prop, expecting the Stainless Steel prop to get me a few more RPMs, but I lost abt 300RPM, and it KILLED my holeshot!...Seems the Stiletto is a more aggressive cup that bites the water harder.<br /><br /> So now I have to rise MY engine to recover the revs & I hope increase the performance! My boat is a 1971 18Ft Modified Vee type with a 1978 Johnson 115Hp. <br />I hope to do the engine lift next week, when I can get some help. Let us know if it improves your holeshot... I am really interested in how this affects things from a dead stop!!! <br /><br />Thanks

 

[Boilermaker]

Re: adjust engine mount

NAVGUNNER,<br />Any update???

 

[Navgunner]

Re: adjust engine mount

Boilermaker,<br /><br /> I had a family wedding in town and havn't been able to do any work on it lately. I have looked into it though and was told you will loose two to three hundred rpms for each quarter inch larger diameter. Then another 2-3 due to the cupped (previous prop was not) prop. So I am having a new 13x19 prop ordered and I guess I will try to find someone who will buy my 14x19 (dealer I bought it from said it is used now and he won't even buy it back from me at a lower price!! Still looks like it is perfect, he won't get anymore buisness from me!!) Once I get the new prop on I will look at rpm's again and then consider raising engine. Nobody has been able to give me any info about engine height affecting hole shot either. I will prob try it just to see. I hope to get out this weekend, so I will let you know. If you beat me to it let me know.

 

[Boilermaker]

Re: adjust engine mount

Good luck!<br />Dhadley seems to be the resident OMC performance guru! I take his advice as gospel. He seems to want to try setup changes before prop changes!<br />From what I have read on the subject (and I read a lot of this stuff, but have limited practical experiance).>>>>><br /> The diameter does not effect RPM anywhere near what the pitch or cupping does. BUT the larger diameter does allow you to run a higher x-dimension (engine hight on the transome). The cupping will also allow for a higher engine set-up & increases the props efficency (how much slippage in the water). The higher you can mount the engine, without loosing cooling water pressure, or allowing the prop to vent & spin, the faster you can go for a given prop.<br /> The lower end of the engine creates a lot of drag, so any decrease in drag will improve speed & overall performance! I just don't know how much it will effect the holeshot???<br />I just got my GPS hooked up today and will get an accurate speed check the next time I go out with my boat. I then hope to change the engine hight & check a few other things to get my old girl going the best she can.<br />I will be making a post with the results of some setup changes. Let us know how it goes for you!!!<br />