Engine Knock

[rocksandhammers]

Finally got around to checking all the valves last night. There was one exhaust valve on the rear cylinder that had a little high clearance, but not by much. Everything else was in spec. I made a point of shining the flashlight in there and really taking a good look at all the valve tappets. Everything looked fine/undamaged as far as I could tell. I also didn't really feel or hear anything unusual while rotating the magneto rotor around to get the pistons at TDC.

One thing I did notice was there was a lot of carbon build up. While peeking down the spark plug hole all I could really see was black, and the rear spark plug had carbon build up, but the front was fine. I pulled the exhaust pipes off and same thing, the rear had a bunch of carbon build up while the front had minimal.


Rear exhaust




Front exhaust (sorry for shitty quality, wasn't as good of an angle)




Looking at the exhaust port on rear cylinder


I also noticed what looked like some oxidation forming on the exhaust headers?


Rear



Front



So now I'm wondering, is this the cause of my sound or just the symptom of the same thing. If the carbon build up could be causing the sound is there a way to clean the cylinders (and exhaust) without removing the engine? Or is the carbon build up likely caused by worn piston rings or something and the that's what's causing my engine noise?

[navigator]

Is that just a shadow or is that a crack in the weld on that pipe?

[rocksandhammers]

Are you talking about what I have circled in red? That's just the carbon that's caked on there that's a little cracked.

[navigator]

No, I mean the dark crescent at 12:00 in the hole.

[rocksandhammers]

It’s just shadow from the camera light. Just went out to double check and don’t see any cracks.

[hillsy]

If the carbon build up could be causing the sound is there a way to clean the cylinders (and exhaust) without removing the engine? Or is the carbon build up likely caused by worn piston rings or something and the that's what's causing my engine noise?

So if you suspect pinging due to excessive carbon build up in the cylinders this should be confirmed by overly high compression numbers. I can't see if you said you've done a compression test?

[rocksandhammers]

If the carbon build up could be causing the sound is there a way to clean the cylinders (and exhaust) without removing the engine? Or is the carbon build up likely caused by worn piston rings or something and the that's what's causing my engine noise?

So if you suspect pinging due to excessive carbon build up in the cylinders this should be confirmed by overly high compression numbers. I can't see if you said you've done a compression test?

I’ve done a compression test recently and talk about it in another post. It was the opposite of high compression. 170 psi for the front cylinder and 180 psi for rear.

[hillsy]

If the carbon build up could be causing the sound is there a way to clean the cylinders (and exhaust) without removing the engine? Or is the carbon build up likely caused by worn piston rings or something and the that's what's causing my engine noise?

So if you suspect pinging due to excessive carbon build up in the cylinders this should be confirmed by overly high compression numbers. I can't see if you said you've done a compression test?

I’ve done a compression test recently and talk about it in another post. It was the opposite of high compression. 170 psi for the front cylinder and 180 psi for rear.

Oh yeah - I remember that thread now - sorry, I forgot it was yours.

So carbon build up is generally caused by oil in the combustion chamber. Your lower that optimal compression numbers would indicate either worn rings or leakage through the valves. Do the compression test again, then put a teaspoon of oil down the spark plug hole and redo the test. If the measurements shoot right up then you have leakage past the rings. If it doesn't change then you have some leakage past the valves. A more comprehensive test is a leakdown test where you hold the piston at TDC and pressurise the chamber (compressed air into the spark plug hole). Then you can hear where the air is leaking out of - crankcase breather = rings, intake port / carb = intake valve, exhaust port = exhaust valve.

[rocksandhammers]

Yeah. That's kind of what I was thinking. Not looking good for my riding plans this summer. Going camping this weekend but I'll try your teaspoon of oil in the cylinder trick early next week and report back the results. Thanks for the tip.

[rocksandhammers]

So carbon build up is generally caused by oil in the combustion chamber. Your lower that optimal compression numbers would indicate either worn rings or leakage through the valves. Do the compression test again, then put a teaspoon of oil down the spark plug hole and redo the test. If the measurements shoot right up then you have leakage past the rings. If it doesn't change then you have some leakage past the valves. A more comprehensive test is a leakdown test where you hold the piston at TDC and pressurise the chamber (compressed air into the spark plug hole). Then you can hear where the air is leaking out of - crankcase breather = rings, intake port / carb = intake valve, exhaust port = exhaust valve.

Alright. Finally got around to testing this out. Got the bike warmed up, but didn’t take the slides out. Figured the increase in pressure was more important than accuracy. Tested before the oil and front was 165 psi while rear was 150. Dumped a teaspoon of oil in each spark plug hole and tested again. Both front and rear went to 170 psi, which is a 20 psi jump for the rear which is the cylinder that had all the carbon. Is this enough of an increase to indicate worn piston rings hillsy?

[rocksandhammers]

Made some progress tearing into the engine and reviving this dead thread since it seemed like the appropriate place to post. Finally got around to building an engine stand with some 2x4's. It's not pretty, but it does the job and it was cheap.



Started tinkering this weekend and got the top end removed and finally got a look at the pistons. Haven't actually done any measuring yet to see if the rings are worn beyond specs, but right away I noticed the pistons seem fucked.





Rear cylinder


Front cylinder


The top of the pistons are heavily carbonized, and and there are 4 indentations from the valves on each. Does this mean my valve timing was off and the valves were hitting the pistons at TDC? The crankshaft and valves don't seem fucked up at all from a visual inspection. This is my first time really digging into an engine like this so any opinions on what's going on here are appreciated. I'm assuming I'll need new pistons?

[hillsy]

The scallops on the pistons are factory - that's to clear the valves. They haven't hit them.

Carbon build up is not too excessive - clean it off and measure the pistons v bore to see if they need replacing.

[DonGee]

I'm adding to this post about knocking only because it deals with octane ratings and that is my real question and I didn't want to get in trouble already for starting a new thread.

Anyhoo, I picked up the bike a week ago Sunday and the previous owner said he always used Sunoco Ultra gas in it. I needed to fill it on the way home and happened by a Sunoco station, so filled it up with the Ultra. Next tankful, I filled with Mobil Super, then I found this forum and started reading all the discussions about octane here. So second last fill up I went with the mid-grade, and this last fill up decided to try regular. No issues so far with any of the choices, but I didn't really expect to notice a big difference right away.

My concern is that reading through the Service Manual that was nicely posted for download here on the forum, I see this tidbit under Fuel:



Well, the pumps here in the U.S. all use that R+M/2 formula for posting octane ratings. That leads me to believe that Suzuki is pretty much saying to use Premium. Are all of you regular 87 users saying that it's really a matter of what the bike seems to run best using? Is the worst that could happen using regular just risking some knocking or could more damage be done long term? Not doubting, just asking. I'd think the Suzuki engineers would have some basis for saying to use 91 or higher.

Okay, so this is weird. That line I quoted/copied is from the section that pertains to my '05 VS800. But at the beginning of the maual under general Information, it says this:



Looks like they changed their requirements over the years.

[navigator]

I've used regular 87 in all my bikes for the last 15 years.
2 of them were bought new and have over 100,000 miles on them.
87 is fine, save your extra money for food.

[WintrSol]

Odd, my FSM says "Use only unleaded gasoline of at least 87 pump octane (R+M)/2 or 91 octane or higher rated by the research method", page 21-12, which is in the '00-'03 model section. They rearranged the words to make it confusing on page 22-12, the '04 section. IMO, they split up the octane numbers from the description of the source of the numbers, and my quote applies. That is because, after I put the Jardine slip-on mufflers on, I could hear the exhaust better, and on 93 it sounded like more unburned fuel was popping in the pipes. Went back to 87, and it sounded much smoother.

BTW, 'pump octane' refers to fuel in the US, which is rated by the (R+M)/2 method.

[DonGee]

Sneaky how they juggle the words around, eh? Well, we'll see how this tankful of regular goes. I'd just as soon save a buck as long as it doesn't screw anything up. Thanks.

[rocksandhammers]

Finally got some time to dig back into things. Took some measurements of things. Pistons and cylinders are good. Piston rings were all below tolerances. Got some new ones ordered, along with new cylinder head gaskets. Came in this week but still in the process of scrubbing the carbon build up off the pistons (any tips for that? I have one pretty clean with a lot of elbow grease using some engine degreaser pads, but I haven’t gotten any out of those divots for the valves).

Before I go about reassembling things I wanted to ask if there was anything else I should take a look at while I’ve got it cracked open? I’m also not sure if the rings were the cause of the sound I was hearing. Definitely had to be the cause of the low compression, but the cylinder isn’t marked up like the piston was banging around in it or anything. At the time it sounded like it was coming from near the cam chain. I checked the chain tension per the manual and it seemed good, but there’s a lot of side-to-side free play in the cam chain guides, which seem like they would make the sound I was hearing. Couldn’t find anything in the manual about the guides so should I just replace them to be safe?

Last question, what’s the correct way to rotate the crankshaft with the top end off to better get at the other piston? I need to raise the front up to get the rings on, but I don’t want to fuck anything up in the process. Thanks for all the help IA.

[hillsy]

If you are this far in you may as well renew the cam chain guides. Then you know they're done.

As far as rotating the engine is concerned you just need to make sure the cam chains don't bunch up at the lower sprocket and lock up the crank. Take off the stator cover and put a socket on the rotor nut - turn carefully and slowly by hand.

[navigator]

If you are this far in you may as well renew the cam chain guides. Then you know they're done.

As far as rotating the engine is concerned you just need to make sure the cam chains don't bunch up at the lower sprocket and lock up the crank. Take off the stator cover and put a socket on the rotor nut - turn carefully and slowly by hand.

Yup take off the cover ...or the center plug, and rotate it Counter clockwise. CCW.

[hillsy]

If you are this far in you may as well renew the cam chain guides. Then you know they're done.

As far as rotating the engine is concerned you just need to make sure the cam chains don't bunch up at the lower sprocket and lock up the crank. Take off the stator cover and put a socket on the rotor nut - turn carefully and slowly by hand.

Yup take off the cover ...or the center plug, and rotate it Counter clockwise. CCW.

Yeah good call Nav - I keep thinking of the LC which doesn't have a plug on the stator cover.