Mercury Sport Jet 120 blown........PLEASE HELP!!!

[HueyLewis]

Hey guys, I blew my sport jet..... Threw a rod right through the side of the block. I can't find an affordable powerhead. Please any direction or help would be appreciated. I am not opposed to putting the 90 in or anything else that would work. Thanks for looking!!!!

 

[HueyLewis]

also, will a force 125 powerhead fit?

 

[RedBarron55]

The outboard will not fit since the splines in the crankshaft are different.
If you do a search using Searchtempest.com on Craigslist you might well find a 120 sport jet engine or a boat with a good engine.
I have seen several as I keep an eye out for a 90.
I found a complete boat with the 90 with good compression for parts for $300.
You can probably find a complete boat for less than an engine.
There are several rebuilt listed on the internet for less than $2000.
The 120 and the 90 have different gear drive ratios so they are not directly interchangeable.
The 120 is 1:1 and the 90 is 1:1.2 or there abouts.

 

[Cobra Jet Steering LLC]

If memory serves me correctly the outboard BLOCK is the same but the intake is different so if your intake is still good and you find an outboard engine that is good you can convert the outboard engine to the jet engine.

 

[RedBarron55]

If memory serves me correctly the outboard BLOCK is the same but the intake is different so if your intake is still good and you find an outboard engine that is good you can convert the outboard engine to the jet engine.

The block is most likely the same and you can use it, but the crank has to be for the Jet, unless the 120 crank splines are the same as the 90 hp jet crank splines etc.

I have NO experience with the 120 hp sport jet.
My guess is that if you are willing to travel a little you might be able to get a boat complete with a rebuildable or runnable engine.

 

[HueyLewis]

well that is a good start. Thank you guys. I am going to keep an eye out for that. Keep me posted if you come across anything in Michigan

 

[RedBarron55]

https://miami.craigslist.org/brw/bpo/d/97-mercury-120hp-sport-jet/6690397526.html
https://stlouis.craigslist.org/bpo/d/120-sport-jet/6658174310.html
https://chicago.craigslist.org/chc/bpo/d/30-storage-unit-full-of/6708889225.html

The above were the results of a Searchtempest search of Craigslist.
A search of ebay might find something as well

 

[Terry Chadwick]

Hey guys, I blew my sport jet..... Threw a rod right through the side of the block. I can't find an affordable powerhead. Please any direction or help would be appreciated. I am not opposed to putting the 90 in or anything else that would work. Thanks for looking!!!!

Hi Huey, sorry to read about your engine problem. I came across your post while trying to get info on the 1998 Sugar Sand Heat Ride Plate. I purchased my Heat 120XR last March and used it this past season with less than desirable performance. I believe my boat's ride plate is causing the boat to not plane out resulting in poor performance. The ride plate facing forward is about 1/4" to 3/8" higher than the hull with part of the gasket exposed. I'm not sure if this is correct as the remaining portion of the ride plate is flush to the hull. The 120XR engine runs great. I might consider selling the boat if the price where right. I apologize in advance if this reply is against Jet Boater's Policy.

 

[RedBarron55]

If the ride plate and the gasket do not seal the area over the plate and exhaust is blown out and sucked into the pump the impeller will cavitate and the engine will rev high and produce little thrust.
If the plate is bent you can perhaps straighten it and install a new gasket.
The boat might well make a good donor for the above as well.
Why did the engine throw a rod?
Did you have oil injection or mixed oil and gas?

 

[Terry Chadwick]

If the ride plate and the gasket do not seal the area over the plate and exhaust is blown out and sucked into the pump the impeller will cavitate and the engine will rev high and produce little thrust.
If the plate is bent you can perhaps straighten it and install a new gasket.
The boat might well make a good donor for the above as well.
Why did the engine throw a rod?
Did you have oil injection or mixed oil and gas?

Thanks RedBarron for commenting. I'm not certain the ride plate is bent or it's simply a matter of the ride plate's front profile being higher than the rear profile. The seal/gasket is definitely showing signs of wear as the previous owner had placed a large amount of sealant around the damaged/cracked ride plate seal. I removed the sealant on top of the ride plate seal and after removing the screws had hoped the ride plate would drop out easily. Such is not the case and I am reluctant to go any further for fear of damaging ride plate and or ride plate seal further. I had hoped to simply clean off the old sealant and start over. My guess is the ride plate seal will be damaged beyond repair should I attempt to pull or pry off ride plate. I will give it another look tomorrow and take a photo to illustrate the issue. A new ride plate seal is in excess of $100.

 

[RedBarron55]

Here is a link to a ride plate seal for your jet
http://www.crowleymarine.com/parts/12290.cfm
$64.99
If the seal leaks then the exhaust will get into the pump and cavitate.

 

[Terry Chadwick]

Here is a link to a ride plate seal for your jet
http://www.crowleymarine.com/parts/12290.cfm
$64.99
If the seal leaks then the exhaust will get into the pump and cavitate.

Thanks RedBarron, that is the seal. The previous owner had tried repairing with marine sealant. I'm going to try and get the ride plate to release from the hull. I suspect some of the sealant is holding in place. I read somewhere that a hot air blower might help with freeing up the ride plate. Any suggestions would be appreciated.

 

[RedBarron55]

The hard part for me was getting the screws that hold the plate out.
That and the inlet grate.
The ride plate needs to be sealed to the hull and the pump body to prevent the exhaust from getting into the pump.
The poor fit as far as streamlining etc probably would not keep the boat from getting on a plane, but a cavitating pump will.
Especially if the wear ring is worn.

 

[Terry Chadwick]

The hard part for me was getting the screws that hold the plate out.
That and the inlet grate.
The ride plate needs to be sealed to the hull and the pump body to prevent the exhaust from getting into the pump.
The poor fit as far as streamlining etc probably would not keep the boat from getting on a plane, but a cavitating pump will.
Especially if the wear ring is worn.

 

[Terry Chadwick]

Yesterday RedBarron provided some insight as to the effect of a bent ride plate and or defective ride plate seal. I've attached three photos of my 1998 Sugar Sand Heat ride plate used with the Mercury Sport Jet 120hp XR. The ride plate was found to be bent most likely as a result of someone trying to correct a leaking seal by tightening the front screws. The seal has deteriorated over time and as a result had seen numerous attempts to correct with sealant. I removed the ride plate and noted sealant between the hull and ride plate and sealant around the interior underside of the ride plate. I will need to straighten the ride plate and replace or remove any sealant as required. Any info as to whether there should be sealant used in the repair and if so where would be appreciated.

 

[RedBarron55]

Sometimes and possible most of the time the ride plate is bent by starting the engine without water on the dealer flush adapter that screws on the hose that attached with the brass flare (large) on the right side of the pump at the rear.
What happens is one the engine might overheat if run long.
More importantly gas will collect on the top of the ride plate and without water to flush it out it can ignite from the exhaust and the explosion will bend the ride plate.
From the manual:
WARNING Never start the engine with cooling water provided by the consumer flushing kit (part No. 22-820543A1). The consumer flushing kit is unable to deliver sufficient water flow to cool the engine, or to purge exhaust gasses from the exhaust system and tunnel area of the boat. Upon restarting the engine, any combustible gasses present in the exhaust system and tunnel area can ignite, creating an explosion strong enough blow the ride plate off the jet drive unit.
The consumer flush kit is the small hose that connects to the top of the block and has the brass check valve on the other end.
The dealer flush kit is basically a brass 5/8 flare fitting like this one at Lowe's
Item # 645731 Model # 48-10-12X P

BrassCraft 5/8-in x 3/4-in Threaded Flare x MIP Adapter Fitting

 

[RedBarron55]

Also when or if you refit the ride plate it needs to have a gas tight seal around the pump housing to keep exhaust and air out of the pump.
The ride plate should be "flat" with the hull as well.
If you or anyone is going to start the engine in the driveway use the "dealer" kit.
You need to have a flow, but not that much pressure maybe 3 - 4 psi.

 

[RedBarron55]

From the manual on using the dealer fitting:
Engine Flushing (Dealer Flushing Adapter)
The engine can be started and run as necessary with a hose connected to the dealer flushing adapter. Do not, however, run the engine at wideopen throttle with no load on the jet drive impeller. 1. Disconnect the engine cooling hose at the fitting on the main drive housing cover. See Figure 9. 2. Install the flushing adapter (A, Figure 10) on the cooling hose (B). 3. Attach a garden hose between a water tap and the flushing adapter. 4. Open the water valve partially—do not use full pressure. 5. Make sure the jet drive is in NEUTRAL, then start the engine. Run the engine at 900-1200 rpm.
NOTE Flush the engine for at least 5 minutes if operated in saltwater.
6. Continue flushing until the discharged water is clean, then stop the engine. Close the water valve. 7. Remove the flushing adapter (A, Figure 10). Reconnect the hose to its fitting on the drive housing cover. See Figure 9.

 

[Terry Chadwick]

Also when or if you refit the ride plate it needs to have a gas tight seal around the pump housing to keep exhaust and air out of the pump.
The ride plate should be "flat" with the hull as well.
If you or anyone is going to start the engine in the driveway use the "dealer" kit.
You need to have a flow, but not that much pressure maybe 3 - 4 psi.

I've ordered a new ride plate seal 8301231 and 2 stator oil seals 819396. I will first need to straighten the bent ride plate and repair the damaged ride plate screw holes. I understand the importance of having a good seal (gasket) 8301231 and a straight ride plate in order to avoid cavitation. What I what to be clear on is the replacement procedure of a new seal 8301231. The attached photos illustrate silicon being using between the ride plate seal 8301231 and the hull. It's interesting to note that none of the silicon seal used between the ride plate seal 8301231 and hull was stuck to the ride plate seal 8301231. There is also silicon around the underside of the inner perimeter of the ride plate close to where the ride plate screw holes are located. I believe I should apply a small bead of silicon sealant around the inner perimeter of ride plate. However is it necessary to remove the silicon sealant affixed to the hull and reapply before attaching the ride plate seal and ride plate? Throughout this text I've stated the use of silicon seal. It may not be silicon seal but some other product. View attachment 84067 View attachment 84068 View attachment 84067 View attachment 84068 View attachment 84068 View attachment 84068

 

[RedBarron55]

There should be no need for silicone around the outer edge of the ride plate as the gasket should conform to the area and seal this area.
A small amount of sealant around the pump to make sure that it seals might help, but again it should not be necessary if the plate is flat, but with yours bent a little might help.
Mostly make sure that there are no voids that exhaust can pass. through.
Clean the sealing area well and expect it to be a tight fit and you will see why extra sealant is not necessary!
A little liquid soap might help get it pushed up in place.