compression - depression

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rhonus

rhonus

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Looking for some advice to cheers me up!!

I have rebuilt my engine from my GSX and couldn't get it to start. Turns out the compression is 50. No I didn't miss the 1 of 150. It is 50 and it drops to 0 on both cylinders. When I stop cranking.

As I mention in a previous post I put the ski in for repair and they blew the engine, mangled the piston into the cylinder head. So I replaced both pistons and all seals on the top end. Cleaned up the head. Re-torqued as per the manual. Obviously there is a leak somewhere. So some questions.

Could the head be cracked and is there an easy way to tell this?
What could I use to check / find the leak. (thought detergent and water might show me some bubbles from somewhere)?
Would it be okay to crank with the cylinder head cover of to test for bubbles if the above is okay?
Should I have had the head milled in case it's buckled from the engine failure?

Any other suggestion to remove the depression I have would be greatly appreciated?

Thanks in advance
Rhonus
 
Did you measure the cylinder holes to ensure that they were the correct size and also not out of round? I assume you used new pistons. Did you measure them for fit? Piston rings, not all lined up and fit the piston correct.

Something major is wrong based on your numbers. Not a little crack in my opinion.


Repairing and selling iPads, iPhones and Mini iPads.
 
If it drops to 0, then your gauge is bad. It should have a valve in it to hold the pressure.
 
Yep, I tend to agree with above, at least part of your problem is the gauge. Get a known good compression gauge and check it again.

That being said if the compression peaks at 50psi, something is definitely wrong. Pull the heads and check the piston size against the bore size. Did you hone or bore the cylinders?

What year GSX, if it's a late model 951 you might want to check the reed valves.

Lou
 
Hi thanks for the responses.

Not sure what happened there typed up my reply and then lost it so here goes again!

Its a 1997 GSX
There was no damage to the cylinders so I didn't see the need to get them honed (though the head had bits of piston in it). I didn't measure them either just purchased the standard one mentioned in the manual. (Doh! have I just blown £250). I got a new compression tester but thought I'd ask some question before I pulled the engine out again.

So as per your advice I'll do the following.
I'll lift the engine out and retest the compression. As the new tester wont fit when the engine is in the craft. If it still drops. I'll remove the head and do some measuring and check this against the box the pistons came in. As far as I could tell the rings were in the correct position. When I first attempted the cylinder replacement the ring moved as I squeezed the cylinder over the piston and wouldn't fit. So fingers crossed they are the correct size.

If I'm unfortunate enough to have the wrong pistons. Then i'll just have to buy the right ones and think on all the experience I'll gain on having to rebuild again. Then I suppose I need to start looking for a second craft which will fit my pistons :)

Thanks again for the advice.
Rhonus
 
If there isn't already, I think we need to make a sticky for comprehensive compression testing. compression testing is not cut & dried. Lots of variables. Gauge accuracy, fittings that displace the spark plug volume correctly, check valves that are on the very tip of the gauge & not through an adaptor (adaptors add chamber volume & lower the reading, especially on small cc engines) , extra oil in the cylinders, engine temperature, cranking speed, etc. There are a lot of misunderstood things, even though it should be a simple test at face value.
 
Sounds like a great idea, do it with some pictures and I'll sticky it, probably best to put it in the how to section.

Lou
 
If the compression gage is not holding pressure it will never give correct results. The 50 psi is only from the first compression stroke. It needs to be able to hold that pressure for subsequent strokes. Get another gage and retest. The compression may be fine.
 
LouDoo said:
Sounds like a great idea, do it with some pictures and I'll sticky it, probably best to put it in the how to section.

Lou
Click to expand...

Sounds like a fun project. I'll work on that & maybe after we can take everyone's input on the details that are debatable, then do an edit to match the common consensus of contributors?
 
rhonus said:
So as per your advice I'll do the following.
I'll lift the engine out and retest the compression. As the new tester wont fit when the engine is in the craft. Rhonus
Click to expand...



If you get one with a flexible hose, you should be able to test it in the ski. You certainly can with my 96 gsx. I would do anything to keep from pulling the motor just to test compression. You will need to do this in the future anyway from time to time, so get one that fits in there.
 
Yeh your right! I've decided to take that one back and have a better gunson on order. This should allow me to leave the engine in and test. Should arrive tomorrow, then I'll let you know what will be happening.

Thanks for the suggestions
R
 
Final had some time to test compression with new tester 152, 155 psi. Just goes to show you get what you pay for! Still won't start. No spark on the PTO side. I think that's how you describe it. It's the Cylinder at the rear of the craft. No spark swapped plugs still no joy with a working one.
Any suggestions welcome.

Thanks
R
 
O.K., try this, unscrew the spark plug caps, trim the wire back about 1/4", and screw the cap back on, see if both cylinders will fire.

If that doesn't fix it, it almost has to be the coil. Coils rarely go bad, but on SeaDoo's both plugs fire at the same time, so something else you could try is switching the plug wires if they will reach, this would confirm it's the coil.

Oh and congrats on the compression.

Lou
 
Hi there

I wasn't quite sure what you meant Lou so I did a search on youtube via google and got this.

https://www.youtube.com/watch?v=nyi_77uAij0

Which when I watched it your message above made perfect sense.

The good new is that if fired up second time. See video

http://youtu.be/LVPh2PQWFHc

Hopefully down to my last few questions There is a small hole just under the towing link water is coming out of this I don't remember seeing this happening before. I think this is normal but wanted to get conformation. See picturephoto.jpg

Just need to run it in now I've read 1/4 throttle from Full tank to 3/4, 1/2 throttle from 3/4 tank to 1/2, 3/4 throttle from 1/2 tank to 1/4 and then I can use full throttle. Is this correct?

Thanks again everyone for your help
R
 
That's completely normal, it's the tell-tale, it lets you know that the cooling system is operating normally, if water doesn't come out then you may have a problem.

Lou
 
Another issue and I think I going to maybe have to strip the engine down again.

I was running it again in the pool last night and was checking some things on the engine when a notice some water. I had seen the last time but put it down to splashes. this time I saw a small trickle. Running from between the cylinder and the bottom end.

2 photos one with out notes and one with so you can see where I'm pointing to properly.

1Before notes.jpg 2After notes.jpg

I'll check the exhaust manifold and make sure it is tight just in case I got muddled and missed doing the final torqueing on one of the bolts. Fingers crossed that this is where the leak is from!

Anyone have any other thoughts or should I just strip it and be done with it?

R
 
Last edited by a moderator:
Hi

That's good to know. I'll see what some of the others come back with and retest tonight and use a mirror to check. I'll make sure I empty the bilge so I can work out how much water I get over a set period of time.
Thanks for the info.
 
Hi chaps

Decided there was to much water so I've pulled my engine. Also my dad had a saying " A job worth doing well is worth doing yersel ". If he'd still been alive he would have told me to pull it and fix it properly so that what I'm going to try and do. I try and put some hematite on both side of the gasket. see if that makes a difference.

One thing I notice was a sludgy oily mess in the pipe cone. I've been running with a premix 40:1 but also had the oil injection working as well. Will this sludge stop happening once the premix done? Anyone come across this before?

Will try and get some photos this time when I rebuild.

R
 
1. The oil is normal with the premix and the oil injection.

2. You need to get those gray fuel lines out of there now! That is probably why you lost your piston the first time. Get those lines replaced and clean the carbs or you will blow this engine too.

3. I like to use threebond 1211 on all the gaskets. It is expensive but you just need a thin coating on the gaskets and I have never had a leak. I usually put some on my fingers and then just rub both sides of the gaskets for a light film of sealant.
 
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