Johnson 88 SPL Powerhead

[longezjet]

Hello All
I'm new to this forum and hope someone can give me some good info.
Just recently a purchased Hurrican Deck Boat with Johnson 88 SPL engine,
looks like late 80 or early 90 model. The only think that i was able to find on that engine is serial number :R8216048 no model number or year, but looking at the engine and comparing to what i have seen on ebay and craiglist looks like early 90 model. Engine has a compression on port side top-120, bottom-115, starboard side top-80, bottom 70. I have replaced the head gasket and the only thing got better was the port side cylinders which were mid 80 psi.
Looking at the top of piston it lloks like the ring got broken and smashed between piston and cylinder head, which leads me to rebuilding it.
I just came across 72 100 hp johnson complete powerhead with cylinders at 135psi. Can i just replaced the powerhead ? Will the exhaust housing on 88 spl match the 100 hp? I read that those engines are almost identical.
Does anyone has manual for any of this engine?
Any info would be very much aprieciated.
Rob

 

[tashasdaddy]

Re: Johnson 88 SPL Powerhead

NO. There are many differences. even between the 88 hp and the 90 hp, of that vintage.

 

[longezjet]

Re: Johnson 88 SPL Powerhead

Really? I noticed that cylinder heads for both engines are identical, they both 90 degree cross flow, and i was told that they share many same parts.
Rob

 

[Haffiman]

Re: Johnson 88 SPL Powerhead

One of the keys to see if parts match up like in this case is to look at the gasket between the parts.
In your case the gasket only covers up to 72 and is not superseeded by later part numbers.
Sorry!

 

[tashasdaddy]

Re: Johnson 88 SPL Powerhead

they share SOME of the same parts!!!!

 

[longezjet]

Re: Johnson 88 SPL Powerhead

Thanks for all the info! So if i won't be able to exchange powerheads because exhaust gasket won't fit, can i just change cylinders, cylinder heads,pistons and adapted to 88 SPL? What are my options if any?
If this would work i will be able to get the engine running and finally enjoy the boat!
Rob

 

[Dhadley]

Re: Johnson 88 SPL Powerhead

The 72 model used a very different ignition and parts are getting really hard to come by. While both are V4 crossflow motors the later model 88 has a lot of improvements. The powerhead mounting bolt pattern will be different too. You'll be much further ahead to rebuild the 88.

The reason the ring broke was probably due to lugging. Once it's rebuilt make sure it's set up and propped out correctly.

 

[HybridMX6]

Re: Johnson 88 SPL Powerhead

Your best option is probably going to be to tear it down, have a machine shop check it out, best case they bore the bad holes, hone the good ones, and you put new pistons and rings in the larger holes, and just rings in the honed ones. You also need to find out what happened to it to cause the ring to fail. Carb rebuilds will be a must, as will water pump assembly. You may be able to get away with having it all done for under $1000, maybe less if one 1 cylinder is messed up, maybe more if others are messed up. This assumes you are doing all the work yourself.

 

[Haffiman]

Re: Johnson 88 SPL Powerhead

You will need access to an aluminum welder, a lath, a milling machine and probably a splines cutter for the driveshaft.
Not to forget the labor!
At the end you will end up with a mechanical Frankenstein!

 

[emdsapmgr]

Re: Johnson 88 SPL Powerhead

The 72 100 hp engine is a small bore block-only 92 cubic inches. The 88/90 is a later block at 99.6 cubic inches. As such, the internals don't share much in common, nor the heads. There is little that will exhange between the powerheads. The reason the powerheads won't interchange is that the bottom of the blocks are different. The midsection adapters are different as a result. The blocks changed in 1978 when the dual thermostat cooling system debuted. The 90 block is worth rebuilding, as it has the newer (3 hole cross-drilled) port maching and will breath better. The ignition and fuel systems are better on the later engine, also.