Tom's 1986 170 Rebuild

[wingnut]

Mwar, you pretty much summed up my sentiments. I will probably scrape it out and squeeze some 3M 4000 into it as best as I can, and call it good enough for a trailered boat.

[wingnut]

Seems I had promised some final numbers on the new prop. Went from at 14x15 to a 13.25x17 to drop the rpms and gain a little top end. Motor is a  1998 Suzuki DT85, max WOT rpm 6000. Ran them side by side for comparison.

Previous
WOT: 31mph @ 6100rpm (too high)
Cruise: 23-24mph @ 5000rpm

Current
WOT: 34mph @5800rpm (perfect)
Cruise 28-29mph @ 5000rpm

WOT speed didn't increase quite as much as I expected but the real gain was at my 5000rpm cruise speed (WOT is kind of a moot point anyway since I don't really run it that high on principle).

I expect if I shed my kicker I'd hit 35. Which is a perfect blend of fuel efficient and speed for my purposes. We have done a few ocean runs and she performs way better than I'd even hoped for.

Hope these numbers are useful for somebody!

[sowers22]

I need some help with the same boat and motor! Having some RPM issue but running the same 1995 DT85 on a 170 with same pitch prop as you and cant get her over 4k RPM ;(

[wingnut]

That's definitely odd... I'm not a motorhead but a couple things come to mind:

Any issues with stalling, hard starting, rpm modulation etc. that would indicate a fuel issue? Have you drained carbs or taken a look at the plugs?

If it is running well, just won't top out...

Have you done a compression test?

Have you messed with or replaced the throttle cable recently? If it can't actuate all the way for some reason, that could limit your top end and you might just need some adjustment.

Finally... have you taken a look at your gear oil recently? If your oil is low or full of metal shavings you could be grinding and limiting your rpm under load.

I'm sure this list is FAR from all-encompassing, but those are the routine/accessible points that I would start with!

[sowers22]

One last question for you sir. What controls and cables are you using ? I've just purchased new ones but they push the throttle cable instead of pull.🙄

[wingnut]

I actually had that exact problem when I first rigged. There is a way to switch your binnacle from push to pull for throttle. It is NOT well documented, and was very frustrating to solve (my DT85 came off a boat with side mount controls, and the binnacle I bought was flipped from what I needed).

Here’s a youtube link that shows how it’s done (it’s for a double Yamaha but fix is exactly the same):

https://m.youtube.com/watch?v=mmROXxoENjQ

Hope this helps!

[wingnut]

My binnacle is the standard Suzuki top mount binnacle (found used locally), standard cables.

[wingnut]

Might as well close the loop on the rebuild as the season winds down.

Got the windshield and grab bag installed a while back, and for all intents and purposes, she is DONE. Anything else will really just be maintenance and upkeep.



Overall thoughts: can't say enough how much I love this boat. It's not big, but it's seaworthy and stable and I can launch it solo in a 20kt crosswind. We've used it countless times this summer, caught a lot of fish and lobster, explored dozens of islands, and generally got the boat grubby any chance we could. Big thanks to everyone on the site for all of the knowledge and help.

Not quite ready for another project yet, but who knows... Maybe I'll nab something locally this winter! I'd really like to find a Sisu 22 hardtop to restore and do small overnighters on, but that may be a ways off.

[Capt. Bob]

Excellent job!
 

[RickK]

Came out real nice - congrats!!

[wingnut]

Thanks guys!

Ran across this gem this morning. Thought about snatching it up and fixing/flipping it, but I figure someone else probably needs a project more than me:

https://maine.craigslist.org/boa/d/portland-175-aquasport-osprey/7216474474.html

[wingnut]

Dusting off my old thread with an engine question for all the 170 owners out there!

Backstory: I currently have a 1998 Suzuki DT85 two stroke on this boat, for those that don't want to read the whole thread. The Suzuki is a known quantity - loud, pretty lightweight, and reliable, if a little cranky. It pushes me at 32mph with full gear load. But, I'm beginning to have doubts about taking a 24 year old motor for any kind of long distances. I currently have a 6hp kicker on the transom for this reason. Taking out kids and family, I like a little redundancy.

Anyway, I just acquired a new project for dirt cheap with a beautiful 2019 Evinrude Etec 75 with a trashed lower unit. The 75 is basically a downtuned 90 and uses the same block. Actually has slightly more displacement than my DT85.

Am I an idiot for considering swapping out? The idea of a basically new, quiet, lightweight, reliable engine is very enticing. With the torque I expect it will pop me out of the water same as the Suzi, with maybe a slight reduction in WOT speed (upper 20s?). If this is the case, I am ok with this. I would also probably drop the kicker if I went this route. To me, the benefits here greatly outweigh the (possible) decrease in speed.

What am I missing? Any and all thoughts appreciated. Yes, I would certainly rather have a brand new 115 hung on the transom but that's not in the cards any time soon.

Thanks in advance!

[Mwar410]

Having a 170 that I run both a 90 and 115 Yamaha  2 strokes on, I much prefer my 90.  Less weight, less fuel consumption and less prop torque for about the same top end (40ish). My 31 year old 90 is going back on it this spring, completely refreshed of course.

[wingnut]

Thanks Mwar, that was pretty much my sentiment. Will update if I make the switch and post some performance numbers.