1987 Thundercraft 18' Ski Boat

[mr eye]

Re: 1987 Thundercraft 18' Ski Boat

I think it's around 4500 to 4600 thats just from memory as i have not run the boat this year. Had it in the water today and the steering locked. Atleast i was still at the dock. I'll get that fixed and give you some better info.

 

[Lou C]

Re: 1987 Thundercraft 18' Ski Boat

That's an OMC Cobra drive with the Chevy 4.3 V-6, same power package I have in mine. I have the 4bbl carb, with that the WOT rpm is supposed to be 4400-4800. if it has the 2bbl it's supposed to be 4200-4600.
These drives are not the ones built as a joint venture with Volvo, they are the last of the pure OMC dog clutch Cobras. There are a couple of things you have to know about them, one is they are fussy about the cable adjustment, so if it jumps out of gear, or doesn't come out of gear, you have to get it fixed right away or the drive can be damaged. The other important point is that the procedure for filling them with gear oil is different than a Merc, you have to drain from the bottom drain on the lower unit, but the fill plug is the next screw up near the joint between the upper and lower unit. You drain it with the dipstick in the top cap (flat plate on top of drive) removed, so it drains. Then replace the drain plug at the bottom of the lower unit. Next rest the dipstick in the hole in the top plate but do not screw in, that allows air to escape and helps avoid an air bubble. You hook your gear oil pump to the fill plug hole that is near the joint between the upper and lower units. You need to get about 2 qts of gear oil in there. Check the dipstick, once it reads full you screw it in, and then quickly remove the gear oil pump and replace the fill plug. Now remove the dipstick and check it again, if low add a little through the dipstick hole. Here are some pix to to make it a little more clear. Whatever you do, DO NOT remove the large screw under the OMC Cobra medallion on the side of the upper unit, the retainer for the screw will fall in the upper unit and you will have to remove the drive to get it out!
Also on the Crowley Marine website, if you look in product support, under OMC drives, it has the procedure from the factory manual for the gear oil change and R&Ring the drive. At this point when you winterize it you should R & R the drive to check the bellows, gimble and ujionts. Note that the pic on the left, has the 3 water drain plugs you have to remove to let the pivot housing drain when winterizing. The pic on the right shows the fill and drain plugs for the gear oil. You can use Merc High Performance gear lube if you cant' find the OMC Hi Vis or HPF gear lube.
www.crowleymarine.com

 

[md-lucky]

Re: 1987 Thundercraft 18' Ski Boat

Lou, that information is FANTASTIC. I cannot thank you enough for the walk through and pictures. I will be using those in the future.

I ran into a small problem the last time out. I'm getting help in another part of the forum. As soon as I tear into it, I will take a few pictures to show what I'm working on and where the leak was coming from.

 

[md-lucky]

Re: 1987 Thundercraft 18' Ski Boat

That's an OMC Cobra drive with the Chevy 4.3 V-6, same power package I have in mine. I have the 4bbl carb, with that the WOT rpm is supposed to be 4400-4800. if it has the 2bbl it's supposed to be 4200-4600.
These drives are not the ones built as a joint venture with Volvo, they are the last of the pure OMC dog clutch Cobras. There are a couple of things you have to know about them, one is they are fussy about the cable adjustment, so if it jumps out of gear, or doesn't come out of gear, you have to get it fixed right away or the drive can be damaged. The other important point is that the procedure for filling them with gear oil is different than a Merc, you have to drain from the bottom drain on the lower unit, but the fill plug is the next screw up near the joint between the upper and lower unit. You drain it with the dipstick in the top cap (flat plate on top of drive) removed, so it drains. Then replace the drain plug at the bottom of the lower unit. Next rest the dipstick in the hole in the top plate but do not screw in, that allows air to escape and helps avoid an air bubble. You hook your gear oil pump to the fill plug hole that is near the joint between the upper and lower units. You need to get about 2 qts of gear oil in there. Check the dipstick, once it reads full you screw it in, and then quickly remove the gear oil pump and replace the fill plug. Now remove the dipstick and check it again, if low add a little through the dipstick hole. Here are some pix to to make it a little more clear. Whatever you do, DO NOT remove the large screw under the OMC Cobra medallion on the side of the upper unit, the retainer for the screw will fall in the upper unit and you will have to remove the drive to get it out!
Also on the Crowley Marine website, if you look in product support, under OMC drives, it has the procedure from the factory manual for the gear oil change and R&Ring the drive. At this point when you winterize it you should R & R the drive to check the bellows, gimble and ujionts. Note that the pic on the left, has the 3 water drain plugs you have to remove to let the pivot housing drain when winterizing. The pic on the right shows the fill and drain plugs for the gear oil. You can use Merc High Performance gear lube if you cant' find the OMC Hi Vis or HPF gear lube.
www.crowleymarine.com

Lou, I was getting ready to tear into this project and I have a question.

I think it was in one of my service manuals, or it may have just been from an old boat mechanic. Where ever the information came from, this is what I was told:

When doing the fluids in the out-drive, I need to remove both plugs and the top dipstick.

Then, I fill from the bottom plug until fluid comes out through the middle plug (also called the fill plug)

Once fluid comes out of the middle plug, I replace the bottom drain plug.

I then leave the dipstick resting on the threads (not seal so air can escape). I then fill through the middle plug until the oil level is on the right spot on the dipstick. Then replace the middle plug and tighten down the dipstick.



Now, what I'm reading with your instructions is that I remove the plugs, then put in the bottom drain plug and fill only through the middle plug until it reads correctly on the dipstick.

I just want to make 100% certain I do this correctly and do not trap any air in the drive. At face value, it seems silly to fill from the bottom and then fill again from the middle, but I also understand that these things are finicky and this may be the only way to get all of the air out of the system.

Any other OMC owners care to chime in with opinions or experience?

Regards,
Mike

 

[keepNitreel]

Re: 1987 Thundercraft 18' Ski Boat

Last post on this thread was sept. 08, you should start a thread in the engine forum for your question.

Good luck

 

[109jb]

Re: 1987 Thundercraft 18' Ski Boat

He started the thread so I personally see nothing wrong with him posting to it even if the last post was sept 2008..

 

[keepNitreel]

Re: 1987 Thundercraft 18' Ski Boat

He started the thread so I personally see nothing wrong with him posting to it even if the last post was sept 2008..

Well I see nothing wrong with it either if he doesn't want an answer. Engine questions should be posted in the engine forum. He started a resto thread not a engine repair thread.

Or PM the guy

 

[md-lucky]

Re: 1987 Thundercraft 18' Ski Boat

Sorry for the detour there. Back on topic:

Decided to start working on the interior. The front seats where going to hell rather quickly. Friends/Family use the front seats to climb in and out of the boat at the docks.. Over this past weekend, the port side broke free from the hinge and cracked.

As you can see from the first pictures in this thread, the interior was pretty much completely trashed when I got it. I decided while I was fixing the seat I may as well reupholster the front of the boat. Here are a few from tonight to show what I started with:

This is as far as I was able to get tonight. I REALLY need a shop at the house. Someday. Someday. I will start working on the rest of the boat as time allows.. Here is what I have done so far.

I also have to figure out how to get the back rests off so I can reupholster them!! Anyone take them off before and have any tips?

On with the pictures!

I had no idea what the heck I was doing, so I started by just tearing the seat completely apart.

I didn't want to deal with the seat breaking again, so I decided to re-enforce the entire thing. It cost me a little room inside the storage areas, but I went around the edges with a 1x4 and straight down the center. I was in a hurry, so I don't have a ton of pictures. You can kind of see the 1x4s in this picture:

Once again, I've never done something like this, so I just went after it:

The bottom side isn't much to look at. I have HUGE respect for people that do this for a living. I got almost all of the wrinkles out, but the corners have a few small ones still.

 

[md-lucky]

Re: 1987 Thundercraft 18' Ski Boat

But the tops turned out pretty good:

Did both of the front side seats, and the seat in the center:

And what I have finished so far. I may put those 3 little tabs in the center of the seats again.. I will have to see if I can find new ones somewhere.

Like I mentioned before, I need to figure out how to take the backrests off next and fix those up. Then I'm going to move back to the rear seats and doghouse. I will probably just purchase new middle seats: I don't have any clue how I could reupholster those bad boys.

After the upholstery is done, I need to do the carpet.. and the boat is as close to "finished" as it will ever be. Still runs like a dream, and with only 3 people in the boat I was able to get 47 on the speedo! I really need to get a GPS and verify the speed..

Hopefully now that the weather is good again I will continue to update this thread with pictures and information. We have very long Idaho winters, so I haven't worked on the boat in months. Last Sunday was the first time out on the water this year for us.. Just too much of a PITA to work outside!

 

[sprintst]

Re: 1987 Thundercraft 18' Ski Boat

Just checking to see if you have any pics of your hinges for your engine cover. I'm looking at ordering some for mine if I can find a supplier...

 

[Nico2112]

Re: 1987 Thundercraft 18' Ski Boat

You're doing a great job mate

Keep it up!

 

[md-lucky]

Re: 1987 Thundercraft 18' Ski Boat

Just checking to see if you have any pics of your hinges for your engine cover. I'm looking at ordering some for mine if I can find a supplier...

This is the best I can do from work with the boat 10 miles away:

They are a 2 piece jobber that screws into the dog-house and the floor. Once you tip it up and forward, you can seperate the hinges and take the dog-house completely out if you like.

I'm working on a barn tonight at a friends place, so I won't be able to touch the boat at all today. When I tear back into the project on Thursday, I will take a better picture of the hinges... That is, if I remember to take the picture. I seem to have developed a bad case of CRS recently.

 

[sprintst]

Re: 1987 Thundercraft 18' Ski Boat

You rock dude. Don't go out of your way on the picture. Take the pic whenever you have some free time if you can

 

[md-lucky]

Re: 1987 Thundercraft 18' Ski Boat

Sprint: I will get them tonight! I didn't want to take the cover completely off last night.. It was late, and I only had about 20 minutes of light to work on finishing up the front. I ended up taking most of the stuff into the kitchen to finish it last night. Good thing the better half works swing shift.

Here is what I got finished yesterday. I just didn't have the time to work on it much last night. Did I mention I need a shop?

But, I'm now 100% convinced magic gnomes built thundercraft boats. I tried like hell to figure out how to get back behind the seat backs to loosen them up.

It can't be done. Period. Unless you pull the entire cap off the top of the hull, there is no way to get back there.

So I went after the front seat back first. Here is what I found:

There ARE screws holding the backs in place. However, the only way you can get to them is if you go through the vinyl:

Pulled all of the vinyl off so I could see what I was working with:

Ah HA! there's what I'm looking for:

May as well get all of the stuff out of the way:

 

[md-lucky]

Re: 1987 Thundercraft 18' Ski Boat

Once you can get to the screw heads, it all comes off. Not a problem at all once you can see them!

The backside of the board:

These are the little nuts that hold the board to the fiberglass. How in the name of all that's holy are you supposed to get to them without taking the vinyl off is beyond me. Anyone else deal with this? Once again, there is NO WAY to get back there with the cap on the boat.

I also decided to add some upholstery buttons to the seats. I will do 3 down the center of the side seats, just like it came from the factory:

Going back together, I decided to just use the Thundercraft plate to hold it to the fiberglass. The only problem is that the other 2 seat backs don't have these plates.. So, I have to figure out a way to make them stay! Any ideas are greatly appreciated!! I'm thinking about hiding a few screws behind the buttons, but that could be a little tricky also.. So, please chime in and let me know what you think!

I'm also thinking I could get a chunk of black plastic about 3 inches wide and run it down the center of the seat, then put the screws through that. It wouldn't be as pretty, but it should hold. It might also match the thundercraft plate in the middle of the center seat. Thoughts?

 

[md-lucky]

Re: 1987 Thundercraft 18' Ski Boat

Sorry it took so long!

But, as promised, here is a picture of the hinges. Let me know if I can help with anything else! I will have more pictures up tomorrow.. I'm ALMOST done with the front of the boat!

 

[Rickairmedic]

Re: 1987 Thundercraft 18' Ski Boat

MD what I had planned to do with my bow rider front side panels was to use velcro to hold the side panels in that was the easiest way I could think of to do it .


Rick

 

[md-lucky]

Re: 1987 Thundercraft 18' Ski Boat

Little more progress....

And then I ran out of staples.. Hard to beleive I've already used 1250 staples!!!!!


I was actually thinking about using velcro! I'm also thinking some high quality snaps may work. If I used a bunch of really nice snaps, I can always take the seats backs off when I clean the boat. That would be really handy! I'm making the decision today.

 

[airmail]

Re: 1987 Thundercraft 18' Ski Boat

Industrial Velcro would be the way to go. If you really want it to stick to the wood on the back of the seats just coat the wood where the sticky side of the Velcro will go with epoxy and let it set up. The tape will stick like its welded on. Great job you are doing.

 

[md-lucky]

Re: 1987 Thundercraft 18' Ski Boat

Hmm. Several folks suggested velcro. Maybe that is the route I should have gone.. This is what I ended up doing. I found these little tabs for automotive trim. This way, I could still remove them if needed...

I used a 2 part epoxy on the back of the tabs, and then stapled them down to the board:

That held VERY well. I was happy with it, but I decided to take it a step further:

Took scrap parts of vinyl and wrapped them around the tabs:

Did that all the way across:

Ready to go back together:

It worked very well!

But, it just wasn't EXACTLY what I was looking for. They just don't have the clamping force that the bolts do. So, the wood wasn't pulled against the boat like it used to... Leaving a small gap between the back of the rest and the boat.

Small enough that 99.9% probably would have ignored it and moved on.

I ran through all the options in my head. I wanted to be able to get out on the water, so I finally caved and put some nice stainless steel screws in the them. I tried to position them where no one would sit and get a nice brand:

And THAT did it. That was EXACTLY what I was looking for. So, I'm going to live with them.