TOPIC: I/O Glasspar Seafair Sedan, need engine advise...

I'm new to this website, and never posted on here before, but hopefully I'm posting this in the right place. Because I would certainly love to get some experience and expertise from someone out there.
I just recently bought a 1967 Glasspar Seafair Sedan w a mercruiser 120 4 cyl I/O. Overall, it's in amazing shape. Everything works, and iv taken it out several times this summer. But it does lack power. It feels like it's dragging anchors. The pickup and go is very sluggish, and I have to get my 2 or 3 friends to move to the bow just to get it to barely plane. I'm pretty sure I need a different prop, but I'm doubting it will help so much that it won't feel like I'm seriously dragging. It feels as though the engine is severely underpowered. So my question is this, should I try and rebuild my 4 cyl motor, or just put in a mercruiser 6cyl? Can the 4 cyl be rebuilt so that it has as much power as the 6? And if I go the 6 cyl route, I will need to put in new motor mounts, and I will have to modify my engine cover. I'm not looking for a speed boat, but since this is struggling to get 10mph, I would definitely like an increase of power and speed. However, I'd like to make as absolutely few modifications as possible. Thoughts??

Welcome aboard Father Goose, glad to have you join us. I'm sure some of the I/O experts will join in here, but I'll throw in my two cents worth in the mean time. The Mercruiser 120 should give you plenty enough power if it's in decent shape internally and properly tuned, include the right propeller. A full tune-up and compression check/leak down test should give you an idea of what's goin on with your motor. I have a hunch you have a lot of power you are not experiencing at this point!?

Upgrading to the 140 (larger 4cyl) would be an option if the above doesn't meet your needs, changing to a 6 cylinder usually involves a lot more changes and adaptations, probably and engine cover/compartment enlargement.

Another important thing to check is for entrapped water or water-logged wood and foam under deck. We've got some serious Seafair Sedan owners here who can direct you properly in the procedure to check things out, but added weight from unwanted water aboard can and does seriously hinder boat performance.

Hope you get her all sorted out, please share some pics with us when you get a chance.

father goose,

WELCOME ABOARD.

ImVho, the 120, 140 & 165 GM inline engines are some of the most thrifty & long-lived of I/O.

Also, you have FOUND the RIGHT PLACE, as this forum has many true experts in a variety of trades/disciplines. ALL of those experts are helpful.

yours, satx

you might (if you can find some) check the way your boat sits at the dock and compare it to pics of other seafair sedans....she very well may have a lot of waterlogged weight under the floor

Welcome aboard and a good compression check wouldn't hurt for sure. I also think an inspection of the foam under the floor is probably in order. Unless the boat has lived in a garage/barn etc while it's not in the water it has probably had water intrusion under the deck and into the foam.

Bob

I have a 165 straight six in an Aristocraft Nineteen. Great engine,but for your boat , I'd go with a 140 as they should swap pretty easy with the 120. The guys here have good advice about checking your floors. Good luck on your foam inspection.jim

Double post, sorry

Several years ago I worked on a 1964 model with a 140 HP inline 6 (194 CID, 2 each 1 barrel zenith carbs) MerCruiser. The engine had a redline of 3900 RPM and the boat happily cruised perhaps in the upper 20s to 30 MPH.

I would expect yours in an "unadulterated" condition should see mid 20s at 4300 RPM (your redline) with I would guess a 15P prop. By "unadulterated" condition I mean properly running in original condition with the original drive or suitable replacement with a 1.98:1 gear ratio. That is also assuming that the boat isn't carrying tons of water weight or excess load.

Since power TRIM was an option power TILT was standard in 1967 you may have TILT and may need to change the tilt pin adjustment but I would expect setting it with the cavitation plate approximately parallel to the keel would be a good starting point.

F.G. Welcome , CONGRATS on a nice model..I also had a 67 SEDAN,but in the outboard version.. A orig 60 H.P. Outboard was good for plaining speed. I would first inspect your electrical spark output... A weak COIL, then dirty ROTOR,, distributor cap contacts... Maybe you have a set of POINTS in the distributor.. if they are very old or PITTED. You will have weak spark,thus low power . Try new spark plugs is also on the menu.. A newer NON- POINTS module would be your first upgrade to install in the distributor.
. Like said above a mechanical COMPRESSION test will determine if a block rebuilder exchange is needed..
The underfloor or STRINGERS of a inboard s motor would have WOOD stringers to support that weight. YES that area couldbe soggy.. GLASSPAR had fiberglass stringers for the outboard, models...
What COLOR would be your SEDAN ?

Well you guys are not only a wealth of information I can tell, you are also friendly as can be, thanks so much! I can tell I am in the right place.
So I really do appreciate all your inputs and I can tell that you all seem to think there is quite likely water weight sponged up under the floor. So I pulled the carpet up, and looked at the entire floor. And there was a small spot or two of a little give, I was surprised how good and decent the wood looked. Now, the wood is screwed down, but on the edges, where the wood meets the fiberglass, it is fiberglassed to the fiberglass sides of the boat. On top of that, the wood floor has a coat of fiberglass on it. So....how can I check the foam and stringers with out tearing up the floor? It may be a dumb question, please just keep in mind Im new to all this. And if there is anyway to mitigate tearing apart something that doesnt need it, Im all for that as Im sure you would understand. Thoughts on how to proceed with floor?? And I took pictures of the floor today, and will post them. Maybe they will help give you further insight.
I will be doing a compression test with the help of my Dad hopefully in the next week or two. And thank you split for the further insight, I am already trying to track down those you items you suggested.
And several of you asked for photos, I will try and upload them right now. I know that just because no visible wood rot or holes in which water could flow into the stringers and foam below, but I will say what I saw looked to be in very good condition if there was indeed water damage underneath.
Again, thank you ALL so much for your input and expertise. Its awful nice to have some folks with experience to bounce ideas back and forth with. Thanks again.

1967 seafair sedan

Exterior

Exterior

120 mercruiser. All original I'm assuming, without any other reason I can see to the contrary.

The floor nearest the rear

Rear floor

Floor

Floor, under engine and motor mounts.

Floor under the carpet in the cabin.

Upper deck floor

Upper deck floor

Mid deck under carpet.

Mid deck flooring.

Nice looker!
If you have a small hole saw that can fit on your 'lectric' drill just drill a hole in the lowest part of your floor (not through the floor )and take a "core" sample. I use a 3" hole saw and save the plug that comes out. If you're happy with the results you can just place the plug back in the hole and glass it back into position.

Thank you much! I sure like her. Ahhh, that sounds like a good approach. But aren't there several rows of stringers? Wouldn't I need to take at least a core sample from each row of stringers? Or is the lowest column of stringer good enough?

Funny you should ask...If there is water present in one part you can almost bet it's throughout the entire bilge. That is a simple way of looking without compromising the integrity of the boat. I have drilled as many as six around the floors of some. With the older boats you can usually see where the stringers are, they are somewhat elevated, discolored etc.
On another subject....hate to rain on the parade but if there is water or soaked foam you might want to check the transom around the outdrive, drill a small hole on the inside if you can reach back there, maybe 1/8" bit and see if the wood comes out dark and damp. Although I/O's don't rely on the transom for motor support they are still vulnerable to rot. There are videos on youtube that cover just about all replacement procedures, some are simple other fellas really go overboard (pardon the pun)
Hope things come out positive for you.
If you do need help with replacing or repairing that beauty there is plenty of help here.

Hey you guys,I hope all is well. I did want to give you an update on where I am with my boat especially since you all offered so much valuable info to help me. So I found an amazing shop here in Salt Lake City, Davidson Marine. I took it to them and not only were they the most polite and helpful mechanics iv ever met, they loved my boat and felt strongly that the power and speed I need was only a tune up away. They performed a compression test that yielded great results. The old spark plugs had heavy corrosion and we're rather old. They felt that all should be well, with it and instead of taking the opportunity to take me for more money, they continuously gave me tips and money saving ideas that i could do to improve its performance. They saved me money left and right. So, I just took it out yesterday to jordanelle. I was blown away. I can best describe it like someone completely swapped boats with me. It drives, runs and performs amazing. Immediately in the water at idle speeds I could easily feel an improvement. And in the open water, she takes off. Plenty of power, more than enough speed and she planes so fast and is smooth as can be. The engine is actually a little quieter. I still can't get over the difference. I couldn't be more pleased. I have to make a shameless plug for both my boat, and my new mechanics and friends at Davidson. The are both in ship shape shape. So look out for one fast and sleek Seafair Sedan out there on the water, I'm gonna be out ALL the time now. And thank you all again so much for your input. I'll try and post more info as she continues to get better and better.

Cookin on the lake with a sweetly tuned merc 120.

Movin along. She definitely has all the power and speed I want/need. So very pleased.

Dream boat being just that.Running like a dream.

Lots to smile about.

Great to hear how well your 120 did. Those inline GM fours and sixes are hard to beat. Just noticed your pics of the floor in your boat. Looks to me like they may have already been replaced.

Great news, glad everything worked out for you. Not too often you find a good shop. I'd let everyone know also.

Outstanding!!!!!!!!!!!!! Congratulations on the shop and the motor. So glad you can take right out and enjoy her!!!

Bob