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**HobbyMan** · 10-09-2006, 06:40 PM

I had a B&S lawn mover do the same thing. It would run fine, but it always burned oil. The cylinder wore down soo much that when the piston was in the cylinder you could rock it side to side. When it would run, sometimes it would get caught in an oscilating motion as the pistion went up and down. RPM would drop, loads of smoke would bellow out, and it would knock really loud. I board the cylinder and put in an oversized piston with new rings and that solved the problem. I don't know if this was the same problem, all I am saying is that my cylinder looked the same way yours does now. Since you were going to boar it out anyway, I wouldn't worry about it any more.

**Geezer** · 10-09-2006, 07:38 PM

That looks like a spot of corrosion from when condensation was corroded the piston to the cylinder wall. It's down low and if there isn't too much clearance, it won't be a problem. I’d clean it up with a hone then measure with a snap gage to see how much larger it is there. You might be albe get away with new rings and having a little knurling done on the pistons.

**trbig** · 10-09-2006, 07:50 PM

This spot is about halfway through the stroke. This cylinder didn't burn any oil, and the exhaust looks great. #1 has the carbon buildup in the exhaust and had low compression compared to the others.. so was assuming that this would be the problem cylinder... not the #2 like it looks like. This piston has never been corroded to the walls (That I know of) and has gone about 6,000 miles until the knocking started.
I am not boring this engine. I want to get it together cheaply so I can ride still while I get a DIFFERENT motor rebuilt. I want to do a few things that are going to take some time, and wanted to still ride while I did this.

Tod

**Geezer** · 10-09-2006, 08:28 PM

The power stroke is pretty well used up by the time the piston is that far down. I'd look the piston over well looking for cracks.

If there are no cracks in that piston, then have it knurled and then hand fit it to the bore. Tell the guy at the machine shop to only lighly knurl it so you won't have to take too much off to get the gap right.

It won't slap after that and you may not be in a hurry to replace that engine afterward.

Geezer

**GNEPIG** · 10-09-2006, 09:13 PM

.. Tod, is this the early motor[78-79] that you had put the XJ head on? and what year cams did you have in this one?

**trbig** · 10-10-2006, 06:20 AM

This is the 78 motor with the XJ head. The 78 cams were used. This motor would make such a racket when it got hot, that I just don't see how this little scuff mark is all that was done. I understand that there won't be a half inch deep GOUGE in it, but what I've seen so far doesn't seem to show anything like what I was expecting. When I took the valve cover off, it smelled like the grease in a vehicle differential that had been burnt.. so I was expecting galded bearings or something.
Also... does anyone know for sure if you can just take off the oil pan to get to the rod caps, or is it absolutely necessary to split the case?

Geezer, with this knurling... do you re-use the same rings? I don't know if anyone around here does that, but I will check.

Tod

**randy** · 10-10-2006, 11:29 AM

Geezer, with this knurling... do you re-use the same rings?

Use new rings and have the walls lightly honed. Ream the ridge at the top of the cylinders or the new rings won't last long.

**Geezer** · 10-10-2006, 11:34 AM

Originally posted by trbig
This is the 78 motor with the XJ head. The 78 cams were used. This motor would make such a racket when it got hot, that I just don't see how this little scuff mark is all that was done.

I don't think that noise was piston slap. Piston slap sounds like a rattle at and idle and usually goes away at higher RPM.

I wouldn't worry about fixing this cylinder unil you've check out the rest of the engine.

Geezer

**DiverRay** · 10-10-2006, 03:16 PM

Have you looked at the cam bearings? I would check the clearance with plastigauge. I would also look at the oil tube going up to the head. If you have a partial block of the tube, you may have been "starving" the head when warm, and causing the noise.
Just something else for you to look at...
Ray

**trbig** · 10-10-2006, 05:25 PM

I took the cylinders, pins, and pistons to a guy today that is going to be doing most of the work on my rebuild. He said there was nothing I showed him that would cause a knock EXCEPT the extra carbon built up on the pistons. He said it's a possibility that after the piston heats up and expands, it could cause a knock against the head. He said the only other thing he thinks it could be is a crank/rod bearing in the bottom. I was told to check for play while holding the crank stationary, but that I should pull out the filter and look at it. If there's copper colored shavings.. that's probably the problem. If there are no shavings... the crank bearings are going to be fine and that I should scrub off the carbon, throw it back together and see if that was it. He told me the rings were pretty loose in the grooves on the pistons, but that it would probably be fine for a bit. The cam bearings all still looked good.
I got sidelined today for a day or two with a chunk of metal in my eye from my grinder last night. Used it for a total of about 3 seconds... felt something hit my eye... but after blinking around and didn't feel anything... assumed it was gone. Today around 11am, was getting worse and worse. I looked in the mirror and could see it there plain as day. They had to dig it out, then scrape away on it a while to remove the rust that had started also. Now I'm miserable, I look like I'm stoned out of my gourd, it feels like my eyelid is scraping on 40 grit sandpaper, and I'm still no closer to figuring the dang bike out! Well... at least I know what it's NOT right now. I will keep you informed

Tod

**Pat Kelly** · 10-10-2006, 05:45 PM

Originally posted by trbig

Also... does anyone know for sure if you can just take off the oil pan to get to the rod caps, or is it absolutely necessary to split the case?

Tod

I currently have the oil pan off my E (2nd gear fix).
Looks like you can get to #2 and 4 rod bearings from underneath. 1 and 3 look inaccessable to me without splitting the cases.

**GNEPIG** · 10-10-2006, 08:51 PM

This is the 78 motor with the XJ head. The 78 cams were used.

.. the reason i was asking: i was wondering if the valve releaf in the top of the older pistons were big enough for the bigger valves of the newer head. the noise grows louder as the engine gets hotter also, very similar to the response of your mechanics over carboned idea.

**Ken Talbot** · 10-10-2006, 09:36 PM

So, just to take this thread in a slightly different direction, what kind of oil were you using when you had the noise. My expereince has been that Tsunami is noisier when I start it up in the spring with the el-cheapo 10w30 I use for winter storage. Once I put the Castrol 20w50 back in for the riding season, it quiets back down.
YMMV....

**GNEPIG** · 10-10-2006, 09:37 PM

.. different part numbers from 79 to 80 [78-79 small valves, 80-up big valves]
79 SG- 2H7-11631-04-46 PISTON (71.46MM STD)
82 XJ- 3H5-11631-00-46 PISTON (STD)

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