Low Top End GT40

TRBenj wrote: Prop down 1/2" and keep running it. I wouldn't touch it unless you really had the desire to do an engine rebuild. 43mph out of a 21' Sport does not seem out of family, especially since you are a little over propped.

Agree completely. Paul, in an earlier post you said "I really have no issues with how the boat runs". You are really so close to expected performance for that boat that it's possible you could do a full rebuild and not see any difference. If you read the props threads you probably saw that these boats seem to vary by 2-3 mph with no obvious mechanical reasons for it.

If you are trying snake oil, I'd put my vote in for Marvel Mystery Oil. Add a bit to the next few tanks of gas. Also, I don't know how much you get out on the boat but there is nothing better than skiing on it as much as you can, putting a load on it and putting hours on it, to clean up a very mild ring problem. I can't imagine with the compression numbers you listed that you have a cracked ring, seems more likely just some rust or cylinder wall scuffing. My usual disclaimer, I could very well be wrong!

63 Skier wrote: Also, I don't know how much you get out on the boat but there is nothing better than skiing on it as much as you can, putting a load on it and putting hours on it, to clean up a very mild ring problem.

This is the advice I got last year when I bought the boat. This season I have done about 50 hours, 20 of which were wakeboarding without any change, hence me trying to go with the snake oil.

I am mostly motivated to learn as much as possible. I have learnt so much this year thanks to this site. Mostly simple stuff but I knew nothing about it a year ago. I've change spark plugs, fuel filters, impellers, oil, Installed perfect pass, wet sanded and buffed gel coat. done gel coat repair, replaced relays and IACV, removed a stuck propeller, lapped a new prop, cleaned throttle body and spent loads of time with my family on the lake. It's been a great year and I guess I am just looking for some projects for the winter.

I would like to rebuild the engine next year after I have bought a new house (hopefully with room to work on the boat). I was hoping there were some thing worth working on this winter to see if I could get things running a little better.

Don't touch it, meaning don't touch it. No snake oil (ever).

Propping down will ease the load on the engine and return better performance. Win/win.

TRBenj wrote: Prop down 1/2" and keep running it.

Any prop suggestions? ACME 1442?

470, 1442 or 654 are all candidates with 15" pitch.

63 Skier wrote: [QUOTE=TRBenj] Prop down 1/2" and keep running it. I wouldn't touch it unless you really had the desire to do an engine rebuild. 43mph out of a 21' Sport does not seem out of family, especially since you are a little over propped.

From 63 Skier "Agree completely. Paul, in an earlier post you said "I really have no issues with how the boat runs". You are really so close to expected performance for that boat that it's possible you could do a full rebuild and not see any difference. If you read the props threads you probably saw that these boats seem to vary by 2-3 mph with no obvious mechanical reasons for it."


After reading this thread, what I get out of it is that you're
happy with the way the boat runs,
had a lot of good family time in it
it doesn't have any other issues
you're new to working on engines (comments like attempting to replace a distributor      cap and rotor make me think this)
you're saving for a new house

So like everybody says leave it alone and drive it.

If you want to get some first hand experience find a dirt cheap (hundred bucks or so) junkyard engine like a 302 or 351. It doesn't need to run. And get a book on rebuilding a small block Ford.

Get yourself an engine stand and have a blast taking it apart and doing plenty of hands on learning as you go. You might even want to put it back together again You gotta be careful though, things like this can get contagious and you'll be looking for more "projects"   

It's one thing to read about it and another to actually have all the pieces right in front of you.

You'll figure out what tools to buy along the way and be much more comfortable when you decide to tear into the boat engine sometime in the future

KenO