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Heavy Knocking Under Load
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Alan Willis
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PostPosted: Mon Nov 13, 2006 3:42 pm    Post subject: Reply with quote

I had the same problem you describe, as was about to tear the engine apart, when I noticed one of the heads had come loose, and was forcing pressure out on a strong load(like going uphill). From the looks of your engine, and the remark of black soot on one of the heads, it sounds like this may be what you were hearing.
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MrPc
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PostPosted: Mon Nov 13, 2006 5:06 pm    Post subject: Reply with quote

Sped, you're right that you can't check the endplay until the flywheel is on. It flops around until then. I don't know how you would check for too much before the flywheel was on. The other guys are right though, if there's too much, then you have to get the case machined. But remember that you'll have to make the endplay measurement and select the right combination of shims to set the endplay to spec, so don't sweat it until you find you can't set it to spec with three shims.

Alan's comment about loose heads is interesting...

Paul
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sped372
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PostPosted: Mon Nov 13, 2006 5:50 pm    Post subject: Reply with quote

The loose head comment is interesting for sure. I really only noticed the "soot" inside each chamber on the left head though, not outside as if it had been blowing out, but still a possibility I guess since I only drove a mile or so after noticing the noise.

I spent some more time sitting in front of everything and forcing myself to look at everything very closely. I noticed that on rods 1, 2, and 3 the wrist pin bushing is nice and brass/bronze colored; on rod four it is a much darker and duller gray. This prompted me to check over the wrist pins themselves (still halfway in their pistons). No visible marks, however, when slid onto it's wrist pin, rod 4 seems to have *some* clearance. I can feel a bit of wiggle or 'tip' if I try. The other pin/bushing fits seem tight. At that time I also noticed that piston 4 has some serious looking markings on one edge above the top ring. They are on the side though, so you can see them when looking through the wrist pin, not 90 to that spot as I would have expected. Cylinder 4 does have some lines in it, but I can't seem to feel them with my fingernail. Could this be another possible clue?

I haven't had much of a chance to check the case itself over yet - I was planning on taking it in to work and going to town with the parts washer anyway. I did happen to see that there appears to be some filler (weld?) stuck into one of the recesses behind cylinder opening 3. I'm pretty sure it isn't supposed to be there because it basically looks like somebody stuck a wad of bubble gum in it, except it seems to be metal.

The adventure continues...
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MrPc
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PostPosted: Mon Nov 13, 2006 5:59 pm    Post subject: Reply with quote

Are the rings all free floating?

Paul
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sped372
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PostPosted: Mon Nov 13, 2006 6:05 pm    Post subject: Reply with quote

Yeah they all seem loose, and I tried the feeler between each one and its land - couldn't get a .004 far into any of 'em so I figured they were ok.
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PostPosted: Mon Nov 13, 2006 7:02 pm    Post subject: Well, Reply with quote

So, what are you going to do when you find out that your timing was way off and it was just your valves knocking? Just curious..........If the noise went away with the clutch in, did it come back if you held the clutch in and rrevved up the engine and held it there?
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sped372
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PostPosted: Mon Nov 13, 2006 7:07 pm    Post subject: Reply with quote

Timing and valves were both adjusted/confirmed ~500 miles ago. The noise was a much deeper rapping than the tickety-tick of the valvetrain.

Anyway, after some more inspecting, I'm pretty sure that my case has seen better days. I found some gouges on the outside, one below cylinder #2:

Image may have been reduced in size. Click image to view fullscreen.


And another in front of #1:

Image may have been reduced in size. Click image to view fullscreen.


I also took a shot of the previously mentioned "bubble gum wad" filler inside the case behind #3 (circled), while I was cleaning a bit I think I may have uncovered a faint crack in the same area (arrow):

Image may have been reduced in size. Click image to view fullscreen.


Some more searching turned up a couple other repairs in the #3 area, one just behind the flywheel:

Image may have been reduced in size. Click image to view fullscreen.


And I think related to it (just on the other side of the large flywheel flange), a large built-up mound of material, it must be weld?

Image may have been reduced in size. Click image to view fullscreen.


Are these cause for alarm? I also just happened to read some favorable posts on the AS21 case - since mine is stamped as such does that influence my decision to keep or scrap it? If this case is questionable I'll probably just go for a longblock somewhere.
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PostPosted: Tue Nov 14, 2006 10:43 am    Post subject: Reply with quote

I come up with a clearance of 0.0065" - 0.0070" between the bushing and wrist pin on #4; seems like too much. As was mentioned, piston #4 also shows scuffing on the top edge and the rod bushing seems to be a darker color than those in rods 1, 2, and 3.

Here is a typical shot of rod bushings 1, 2, and 3 - nice and bronze/brass colored:

Image may have been reduced in size. Click image to view fullscreen.


Here is a shot of bushing 4 - darker in color and just looks different:

Image may have been reduced in size. Click image to view fullscreen.


And here is a shot of the scuffing along the top edge of piston #4, maybe the extra bushing/pin clearance allowed for some "tipping" ?

Image may have been reduced in size. Click image to view fullscreen.

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PostPosted: Tue Nov 14, 2006 1:44 pm    Post subject: Reply with quote

Neat. Nice pics.
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sped372
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PostPosted: Wed Nov 15, 2006 9:29 am    Post subject: Reply with quote

As a follow up to this - Bentley specifies new pin/bushing clearance of 0.0004"-0.0008" with a wear limit of 0.0016" - mine is clearly out of tolerance. Even if it wasn't responsible for the noise it still makes me feel like it was worth taking things apart. That, and finding out that the case had repair work done on it - now I just have to decide whether to rebuild (using a questionable case for a foundation) or opt for a longblock.
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