gt150 powerhead replacement

[wyngo]

Currently have a 1989 gt150 with a blown powerhead and am looking to replace with a powerhead from 1982. Is there anything that I should be concerned about between the two ? As far as I can see these are pretty much the same powerhead.

 

[emdsapmgr]

Re: gt150 powerhead replacement

The powerheads are pretty much identical. You will need to work through these differences:
1. The late model powerhead has special bolt hole bosses on the outer exhaust cover for mounting of the power trim box. Your older engine does not. You can switch the covers, as they are otherwise the same. 2. The newer engine has a combination oil/fuel pump which has mounting, wiring, vacuum switch and fuel plumbing issues. You might want to consider not installing the OMS fuel pump, and go with the old double premix pumps instead-it may be a lot easier. 3. The fuel primer systems are different between the two engines-your early powerhead may put the fuel it at the intake side covers instead at the carbs. 4. If the new 150 is an XP/GT model, those are the large carbs, and you would want to run them instead of the 82 carbs. 5. If the late model engine is an XP/GT model, you may want to run those heads as the 82 may have low compression bathtub heads. One advantage to the old ignition system, it could have two original unlimited rpm power packs.

 

[Dhadley]

Re: gt150 powerhead replacement

Any 149 cid crossflow V6 block with the flat exhaust plates will work. Look closely at how your ignition components bolt up compared to the replacement block. You'll be much happier if the replacement block has the 200 port timing.

 

[Dhadley]

Re: gt150 powerhead replacement

And regardless of which powerhead you use stay with the XP/GT heads.

 

[wyngo]

Re: gt150 powerhead replacement

I would like to thank everyone for thier input, it is very much appreciated. The 89 unit is a j150stlcem and the 82 is a j150txcnm, The 89 is a gt and I believe the 82 is as well. The 82 is a rebuilt block and has the heads on it so I will be looking to transfer all the other components ( carbs,powerpacks and such ) from the 89 to the 82, and it sounds like there will not be many issues in order to do so. Once again thanks for the help.

 

[Dhadley]

Re: gt150 powerhead replacement

The model number of the 82 does not indicate it's a GT but was rather from a 25" motor which is OK but it's not a GT. Some of the 150GT / XPs had 200 port timing so don't be surprised if the replacement isn't quite as strong as the original. If you don't use XP/GT heads there will be a difference.

 

[wyngo]

Re: gt150 powerhead replacement

I can live with the loss in power ( at least for a little while ), and this will give me time and expierence in fixing the 89 powerhead. The 89 had scoring on the #6 cylinder. The piston is toast, but the cylinder walls do not look that bad. At least I can get back on the water, and let the finances dictate how fast the 89 can get rebuilt. Once again thanks for your help.

 

[emdsapmgr]

Re: gt150 powerhead replacement

If you don't transfer the heads, I'd run the original 82 carbs. The larger carbs from the 89 may overfuel the powerhead and give unsatisfactory performance on top end.

 

[wyngo]

Re: gt150 powerhead replacement

Well the weather turned out good and I have started to swap out the powerhead. My concern is the fuel primer system as the old block has it entering through the intake side covers. Should these be changed with the ones from the 89 or is there a way to block these adapters?

 

[Dhadley]

Re: gt150 powerhead replacement

Injection into the intake right behind the carbs is the most efficient choice. You can just cap off the brass nipples if you don't use them. If your by-pass covers have 2 nipples and you don't need either just connect them with a short piece of hose.

 

[wyngo]

Re: gt150 powerhead replacement

finished installing the powerhead with not too many problems, but it would not start. Dropped it off at the shop and needed a new powerpack and coil. Went to the river and turned it over acouple of times until a heard a "tink". Ended up beaking the bendix on the starter. Never saw that before. Got a new starter and still could not fire her up. Brought back to the shop to find out that I am stupid. After a quick lesson on how to start her, I went back to the river to run her. Ended up spending an hour that night picking bugs out of my teeth. Will let you know how she runs after the break in. Thanks for all the help.

 

[wyngo]

Re: gt150 powerhead replacement

Made it through the breakin period and some other issues. The Break Out Another Thousand rule is true, as it is one thing after another. The engine runs great and am very happy, although expected to be a little faster. I am going to put the 89 heads on and change the prop to see if i can get a little more out of her. Once again thanks for the help.

 

[jonesg]

Re: gt150 powerhead replacement

Look on the bright side,
if not for the help the guys gave you here it would be ;

Break out another THREE thousand.

 

[wyngo]

Re: gt150 powerhead replacement

Well I ran the replacement powerhead to hard, and blew a hole in the side of it. Brought the original powerhead to the machine shop, and was told that they can hone it to .010. If I have this done what pistons do I use, or should I have them bore it to .020? Thanks in advance.

 

[proaudioguy]

Re: gt150 powerhead replacement

Well I ran the replacement powerhead to hard, and blew a hole in the side of it. Brought the original powerhead to the machine shop, and was told that they can hone it to .010. If I have this done what pistons do I use, or should I have them bore it to .020? Thanks in advance.

Not trying to be a douche, just being a noob and all (me), I was wondering if you could tell me what NOT to do so I won't blow up my engine. AKA, how did you do that? I do not have "another thousand".

 

[Dhadley]

Re: gt150 powerhead replacement

First, running the motor hard will not blow it up unless you zing it up without a load on the prop. Second, if you have them bore to .010 over what are they going to use for pistons and rings? Third, what happened to the powerhead? How do we know if you put all the dressing on yet another powerhead the same thing won't happen?

Not getting a real warm feeling about your repair shop right now.......

 

[emdsapmgr]

Re: gt150 powerhead replacement

If you are going to oversize one bore and use a factory piston, you will probably have to go .030 over. I wouldn't mix various manufacturer's pistons in an engine. When you switched to the XP/GT heads on the engine-were you using the 1982 carbs, or did you swap to the larger XP/GT carbs at the same time?

 

[proaudioguy]

Re: gt150 powerhead replacement

Excuse my ignorance about outboards, but .010 should work fine wiht oversized rings, should it not? I would not think you would need to replace the pistons assuming they are in good shape. Still wondering where the hole came from.

 

[wyngo]

Re: gt150 powerhead replacement

What happened was the rod cap in the #4 cylinder blew when I was running at high speed. The prop I was using could go to 6000 rpms on a light load and unfortunately I had it there a couple of times not paying attention to the tach, and was told that this could cause this to do that. I usually ran it around 5500, but every now and then I would push it further. I never changed the heads out as it was running good, and figured why mess with it.I used all the components from the '89, and besides the heads, I could not tell the difference in the blocks. I was fishing a tournament with full gear from both myself and my partner, both livewells were full with water and 15.6lbs of fish and was running about 46mph at 5500 to 5600 rpms when it blew. It sounded funny earlier, but we had our rain gear on and figured it sounded different becuase our rain hoods where on. I asked about the honing due to budget reasons, and after seeing the cylinder walls they really were not that bad. I was hoping to reuse the old pistons as I have nine of them. I could not see where I would be able to do this so I figured I would ask. I will have them bore the cylinder and then put it back together. I saw pistons for .020, but do agree with using OEM equipment so will probably go that direction. Will let you know how it works out. Fortunately I have a smaller boat, so fishing season is not over yet, it just begining to get good.

 

[wyngo]

Re: gt150 powerhead replacement

What happened was the rod cap in the #4 cylinder blew when I was running at high speed. The prop I was using could go to 6000 rpms on a light load and unfortunately I had it there a couple of times not paying attention to the tach, and was told that this could cause this to do that. I usually ran it around 5500, but every now and then I would push it further. I never changed the heads out as it was running good, and figured why mess with it.I used all the components from the '89, and besides the heads, I could not tell the difference in the blocks. I was fishing a tournament with full gear from both myself and my partner, both livewells were full with water and 15.6lbs of fish and was running about 46mph at 5500 to 5600 rpms when it blew. It sounded funny earlier, but we had our rain gear on and figured it sounded different becuase our rain hoods where on. I asked about the honing due to budget reasons, and after seeing the cylinder walls they really were not that bad. I was hoping to reuse the old pistons as I have nine of them. I could not see where I would be able to do this so I figured I would ask. I will have them bore the cylinder and then put it back together. I saw pistons for .020, but do agree with using OEM equipment so will probably go that direction. Will let you know how it works out. Fortunately I have a smaller boat, so fishing season is not over yet, it just begining to get good.