Merc 420 Cyclone engines

MOBILEMERCMAN · Jan 23, 2021

Good news on engine centers. I thought bravo tails were shorter; I must have thought wrong. I was working on boats when 420's first introduced Gils. They had mufflers. Too much time has passed to say if all had mufflers. Polished stainless not aware of coated.

What year is the boat? Do you know the original engine serial numbers?

It is helpful your original tails have part numbers on them.

BDC1013 · Jan 24, 2021

MOBILEMERCMAN said:
Good news on engine centers. I thought bravo tails were shorter; I must have thought wrong. I was working on boats when 420's first introduced Gils. They had mufflers. Too much time has passed to say if all had mufflers. Polished stainless not aware of coated.

What year is the boat? Do you know the original engine serial numbers?

It is helpful your original tails have part numbers on them.

The boat is an 89 I believe. I don't have the engine serials handy but previously I did and that's how i found the mercruiser part diagram showing the tail pipes with the mufflers.

https://www.crowleymarine.com/mercury-outboard/949.cfm

I believe that is the link and the engine serial number may be (42006877) ?

Ratickle · Jan 25, 2021

It should have the HIN on the transom I believe. If you find that, the year can be figured out.

BDC1013 · Feb 17, 2021

Ratickle said:
It should have the HIN on the transom I believe. If you find that, the year can be figured out.

Looks as if the plate that it would be stamped on is missing on the top right corner or the transom. I have the title though, says its an 88.

BDC1013 · Feb 17, 2021

I found some spare props for a decent price. Not sure if props are something i should have spare of or if they are a good idea to purchase to play around with size and pitch. My knowledge of props is very little.

i Currently have 3 blade clever style 19 spline 15x24" P L&R

The other two sets for sale i found are:

3 blade clever style 19 spline

16x25.5" P L&R

17x28" P L&R

Worth picking up for spares and/or to try for speed/function of boat? What would these do vs. what mine are?

Boat weight: probably 10k
HP 500 a side
Non stepped V hull

Current update of boat: Upholstery complete, Fuel tanks back in boat and floors re-caulked, drives painted and ready to install. Next step is to fire port side engine and run it in the boat. Was going to do this before putting the drive on just incase there's an issue and the engine needs to come back out. Should be fine to run with the drive off right?

fund razor · Feb 18, 2021

I like having spares. I have a cleaver style set that came with my Apache I never tried. But they ride in the boat in case of prop mangling. (We have low water.) I have had good results with my Bravo One four blades. If they are cheap, maybe grab the set that are closest to what you have. At some point or another, Brett at BBlades gets his hands on all of my props to fix any small issues and true them up. I never feel confident they are really balanced until he does.

MOBILEMERCMAN · Feb 18, 2021

BDC1013 said:
Looks as if the plate that it would be stamped on is missing on the top right corner or the transom. I have the title though, says its an 88.

It would be good to find it marked somewhere else in or on the boat. Sometimes it will also be marked on a center stringer. Or get it replaced to prevent future issues that may arrive.

MOBILEMERCMAN · Feb 18, 2021

Did the 15x24's come with the boat? If so gives you a base line. If so my guess would be the 420's would turn them 5400. I would also guess the 500's would turn them 5800 ish.
There is no set formula on what you ultimately need. Many variables include diameter and pitch. I think the 16x25's would be close to your target I'm guessing to be 5300. It should say on flame arrestor. I don't think you'll turn 17x28's. I find it very unlikely you can get them in the recommended RPM range labeled.
Last thought. An under propped pleasure boat is much more fun then an over propped boat. Over propped is also hard on engines and drive line.
Prop pitch is the simplest terms is the final gear of the package. Too big size and /or pitch is like pulling off a light in a truck in 3rd gear.

MOBILEMERCMAN · Feb 18, 2021

When you find what the boat likes a spare set of an inch different in pitch would be nice to have. In general 1 inch pitch will change rpm 200r's. Given same diameter and style. Diameter has a large effect in r's and handling compared to pitch.
In the short term don't get too hung up on props. Boat should test fine with original. Just don't over rev them. An under propped boat will pull hard and may or may not slow down.
I like 26's on mine best. They turn 5800. I am under the belief, from all my years, more pitch will break more parts in my overpowered drives.

BDC1013 · Apr 4, 2021

She's in the water! Thank you all for your patience! :driving:

https://www.facebook.com/508792430/videos/10159255805452431/
https://www.facebook.com/508792430/videos/10159270975122431/

MOBILEMERCMAN · Apr 4, 2021

Not a facebook guy and can't see links.

I am glad your perseverance paid off just in time for summer.

Bobcat · Apr 4, 2021

Good Lord...Don't You People Tan ???

Man, that looks great...Sounds good too!!!

BDC1013 · Apr 4, 2021

Bobcat said:
Good Lord...Don't You People Tan ???

Man, that looks great...Sounds good too!!!

HAHA its the end of winter, dont worry this should be the most tan ive ever been in my life after this summer!

thank you, shes about 95% done and first test run went without any issues. Time to button up all the rest of it and that sucker polished to enjoy the summer!