engine knock on deceleration

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crf_kdx
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engine knock on deceleration

Post by crf_kdx »

Hey folks!

I was about ten miles into a ride today when the ole KDX developed a relatively loud engine knock on deceleration. I didn't hear the knocking anywhere else . . . just above idle upon slowing down. Since my son and I were near a trail head, I took his bike back the 10 miles and got my truck. I wasn't brave/foolish enough to ride 'er the ten miles back to truck. In the brief period when I was trying to figure out what was going on I didn't notice any drop in power - just the knocking as I slowed to go into corners.

My '05 KDX has about 3500 miles on it and I've not even peaked inside the engine yet. (Well, I look up the exhaust when I replaced the pipe but didn't see much.) I had planned to replace the top end in November after the last HS of the season. I'm hoping a top end will do it but I wanted to ask what I might specifically look for as I open her up in the next few days. I have recorded compression tests periodically and I thought I do that before I started to tear it apart. I also thought I'd put a stethoscope on it to see if I could hear just where the noise might be coming from although I'm a little uneasy about running the engine too long.

For the sake of completeness, I did overheat the girl a couple weeks back in a HS - she puked out quite a bit of fluid. I had a 40 mile ride on her last week though and I didn't detect anything unusually.

Any words of wisdom would be appreciated!

Kirk
"There are two kinds of adventurers: those who go truly hoping to find adventure and those who go secretly hoping they won't."
~ William Trogdon

2002 Honda Shadow ACE 750
2005 KDX 200 (mine)
2006 CRF 250X (son's)

2004 TTR 125LE (for sale)

KORHS Series: Senior C
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jrock
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Post by jrock »

make sure everythings tight on it...my 50 sounded like the engine was knockin on it the other day and i then i seen the gas tanks rubber thing fell off and it was just vibrating
IdahoCharley
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Post by IdahoCharley »

Could be piston slap due to piston/cylinder wear. At 3500 miles a worn out piston is very likely. Look on the thrust surface area of the piston for signs of excessive wear and note your piston ring end gap measurements for future reference. Got to run........

P.S. Should go without saying - check your rod bearing and main bearings for play and note the side clearence on you rod for future reference.
KTM 380EXC Mine
KDX 200 Mark's
TTR 125 L Wife's
KDX 200 Austin's
EC 300 Tyson's
WR430 Husky - mine
crf_kdx
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Post by crf_kdx »

I got around to doing a compression test tonight . . . the results follow:

10-29-05 @ 330 miles: 162 psi
3-25-06 @ 830 miles: 165 psi
3-17-07 @ 2400 miles: 165 psi

Today @ 3500 miles: 158 psi

That's only about a 4% drop over the average of the first three compression tests. Hell, that's probably within the range of human error and even if accurate isn't much of a drop in pressure! I've ordered the parts for a new top end but based on just the compression test I'm a little worried my woes may be more serious. Btw, in warming up the bike to do the compression test I couldn't get the girl to knock but Austin confirmed I wasn't hearing things last weekend.

The parts from RMMC shoud be here Friday . . . I guess I'll tear into it this weekend and see what I discover.
"There are two kinds of adventurers: those who go truly hoping to find adventure and those who go secretly hoping they won't."
~ William Trogdon

2002 Honda Shadow ACE 750
2005 KDX 200 (mine)
2006 CRF 250X (son's)

2004 TTR 125LE (for sale)

KORHS Series: Senior C
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Oldschool
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Post by Oldschool »

On mine it was the play that the countershaft sprocket has between the
clip that holds it on and the cases.
When I let go of the throttle the chain throws it up against the clip,
Sounds just like a knock.
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