Sea Doo 951 Knocking Sound (newly rebuilt)

[NCGator25]

Looking for suggestions on what could be causing the knocking sound on my recently rebuilt 951 (carb).

Engine builder thought it might be getting water in the cylinders. I pulled the exhaust pipe. The engine passed both cooling system and engine leak down tests. Put everything back together, and it still has the knock with no water running through it.

Here's a video of the sound.

 

[Boyd12]

That is pretty bad. Have you found out the source?

 

[gefakoc]

Have you?

 

[NCGator25]

No, I haven't been able to find the cause to the loud ticking. Water was getting into the cylinder. Prior to removing the engine, I took the pump off, and ran it without water running through it. It still had the ticking sound. Then, I hooked the hose up, and the sound was still there.

Video of engine running without the pump, and without water running through it:

Once I hooked up the water, the engine struggled and almost shut off. That's when I decided to pull the engine out.

I'm glad I decided to run water through it one last time. After removing the head, I found that water was getting in below the head gasket (see pics). The builder used Permatex Indian Head Gasket Sealant between the gasket and head, but not between the gasket and cylinder housing, and it appears that's how it was getting in.

I'm trying to measure the pistons, etc. now. The builder doesn't think it needs a new top end since it only had 15 hours on it. I may just need a new seal kit to put it back together. I'm debating on whether or not to have a local shop deck the head and housing to ensure they're flat.

If anyone has thoughts, please feel free to share...

 

[FL-Rider]

You can measure the cylinder diameters without removing the cylinder using the right tool. Then check the stamp on the pistons to see if they are standard or oversize. Ultimately you might have to remove the cylinder anyway, but that can give you an idea. Check your head with a straight edge to see if it's warped. After re-assembly, do a leak down test of the assembled engine to confirm it's air-tight. You will have to acquire or make block-off plates with gaskets to do the test.

 

[NCGator25]

An update....

What would be your next step be if you were in my situation?
I had my 951 carb engine rebuilt earlier this year at a cost of $2k (included shipping). I got 15 hours out of the engine before it started having problems. I broke the engine in using premix for the first tank, etc.

It was discovered that water was getting into the cylinders under the head gasket. I have pictures of this. It was not coming in from the pipe gasket. I pulled the engine from the boat.

After discussing the situation with the builder, we thought I could put everything back together since it was unlikely any of the new parts had worn significantly. After taking the top end off, I had a local machine shop deck the head and cylinder. He didn’t need to take much off, but said the inner portions of each were lower than the outer edges, so I’m glad I had this done.

The builder sent me a seal kit to put everything back together. I didn’t split the case since everything seemed fine with the new crank that was installed. I put everything back together, but the engine is still making the horrible sound after running it. There’s no water getting into the cylinder. See Youtube clip below. This was taken prior to pulling the engine, but the sound is the same.

Engine Stats:
Engine passed leak down tests for cooling system and engine.

Squish – I wasn’t able to get a reading after pulling the engine and measuring, so this was out of spec when it was rebuilt. After the head and cylinder was decked, I was able to get .9 and .91, so it should be within tolerance now.

Cylinder wall clearance – Mag was in spec .4-.5, PTO was out of spec at .6. WSM pistons were used. I had the machine shop measure these.

Ring Gap – Mag was in spec at .18, PTO out of spec at .22.

Carbs – accel pump was removed, 90 low speed jets installed (1.5 turns out), stock high speed (0 turns out).

Here’s the clip (same as first post): https://youtu.be/6gYpwY7tK7s

So, what would you do next to find the problem?

 

[Grim]

My question would be what caused you to rebuild the engine. Was it not running right or was it just worn out. Most people rebuild because of a problems and then forget to make sure the problem has been fixed. If the engine itself is not the problem then you haven't fixed your issue, It can ruin a new engine quickly too. So what was the symptoms of your issue with the old motor? Did you rebuild carbs with this engine overhaul?

 

[etemplet]

First time I clicked on the thread. On the first video the noise doesn't sound like an engine build issue. Engine is just a pump. Definitely weird.
A simple compression test will let you know if a newly built engine is OK. You might have a reed valve issue. Good Luck !!

 

[mikidymac]

Easy to rule out the engine, pull the pump and driveshaft. Much easier that messing with the engine at all.

 

[FL-Rider]

Could it be piston slap? The first and third videos sound kinda like it. The second video with the pump off and slightly higher rpms didn't sound as bad. I had a 951 do something similar. It was after it had a head gasket leak and water ingestion. At idle I could hear it. Above idle it got quieter. When you had the cylinder measured, did they measure it in multiple locations? Did they measure the piston in multiple locations? You say the PTO has more clearance than the MAG...

 

[mikidymac]

Just so we are clear, nothing on a new engine should ever be out of spec.
Piston slap on a 951 will fail catastrophically in very short time and take the entire crankcase with it.

 

[NCGator25]

My question would be what caused you to rebuild the engine. Was it not running right or was it just worn out. Most people rebuild because of a problems and then forget to make sure the problem has been fixed. If the engine itself is not the problem then you haven't fixed your issue, It can ruin a new engine quickly too. So what was the symptoms of your issue with the old motor? Did you rebuild carbs with this engine overhaul?

Last year, I burned a hole through the mag piston, which required the rebuild. The engine had roughly 155 hours on it at the time. There were other issues as well. The start/stop button was bad which was causing the engine to shut off. At the time, it seemed like there may be an issue with the stator. The RPMs were also jumping all over the place.

The carbs had been rebuilt with mikuni parts (needles and seats too) prior to all of those things and set to factory specs. But, with all of those things happening, and the subsequent adjustments to try to fix it, led to the engine failing.

 

[NCGator25]

First time I clicked on the thread. On the first video the noise doesn't sound like an engine build issue. Engine is just a pump. Definitely weird.
A simple compression test will let you know if a newly built engine is OK. You might have a reed valve issue. Good Luck !!

I did run the engine without the pump attached and it still has the same sound as the first video. It sounds the same after the redoing the top end recently, and ensuring the pistons cylinders, ring gap, etc were in spec. It's definitely an engine issue.

The compression on my gauge is 120-121 on both cylinders. I know this is low, but I've read that it should be run fine at those numbers. Also, I checked the compression numbers again after I put it back together and they were the same. This was after surfacing the deck and with the squish now being within spec. I do not believe it was in spec after the rebuild.

I've also read the WSM pistons are shorter than OEM, so I don't know if some of these builders are taking that into account when they rebuild them.

I checked the reed valves when I had it out of the boat, and they are in good shape.

 

[NCGator25]

Easy to rule out the engine, pull the pump and driveshaft. Much easier that messing with the engine at all.

I've run it without the pump attached, and the loud noise is still there.

 

[mikidymac]

If it is the engine knocking I would suspect the crank or balancer.

 

[NCGator25]

Could it be piston slap? The first and third videos sound kinda like it. The second video with the pump off and slightly higher rpms didn't sound as bad. I had a 951 do something similar. It was after it had a head gasket leak and water ingestion. At idle I could hear it. Above idle it got quieter. When you had the cylinder measured, did they measure it in multiple locations? Did they measure the piston in multiple locations? You say the PTO has more clearance than the MAG...

I initially thought it was piston slap, and mentioned to the builder that's what I thought it was. However, now I don't think it is. It's too loud of a noise to simply be that. Yes, the PTO cylinder bore is a little larger than the MAG.

The machine shop measured for me, but didn't write anything down. I gave him the specs from WSM, and asked him to check it. The cylinder wall clearance for the MAG was at .005, and the PTO was .006 (out of new spec for WSM, but I certainly still within an appropriate range to run). He measured at the top and bottom of the bore. The MAG was the same, the PTO was slightly larger at the bottom. I did not ask him about measuring the piston separately, I was only concerned about the clearance. He had the pistons though.

WSM's spec:

 

[NCGator25]

If it is the engine knocking I would suspect the crank or balancer.

This is more and more what I'm thinking too. What's interesting though, is the engine will run fine for a period of time, then the noise starts. After rebuilding the top end, I put it in the water, and it ran fine for about 10-5 mins, then the noise returned as I was heading back to the ramp.

I have the carbs out of the both again to check them, but as I've thought about it, I don't see how the could be causing the issue. I'd think it wouldn't run well at all if something was wrong with them. I almost bought new carbs, but decided to try to figure things out first.

I think my only option is to pull the engine again and open the case to see what's going on. I don't want to pull the top end apart again if I don't have to since the seal kits get expensive!

 

[etemplet]

Get a engine stethoscope and poke around while it is running. It will get you close too or right on the noise source. You'll definitely found out what it isn't. You could have a bad bearing. Might have a bolt that is too long or in the wrong location. This will help you find it. Good Luck !!