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General Category >> Rubber Side Down! >> Any clues before you drop a valve?
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Message started by BurnPgh on 11/14/09 at 22:20:08

Title: Any clues before you drop a valve?
Post by BurnPgh on 11/14/09 at 22:20:08

Only thing Im worried about after having done all the work I did is dropping an exhaust valve. My exhaust valves are pretty beat up but I didn't have the cash at the time to get new ones. I will be fixing that come spring time. Its been all good until today. I got some funky noise. Im not even sure how to describe it. Accelerating from 30-40ish I might get a kind of wooshing sound...sort of. I can imagine it could sound like a cam chain failure but my chain/guides are brand spanking new. less than 500mi. Seems to come from the front of the bike. And is speed dependent but not nessecarily RPM dependent. The one time I got it to make the sound and was about to pull in the clutch to see if it kept going it stopped right before i pulle dit. I really dont even know how to describe it but if it isnt/there isnt a red flag that im about to drop a valve im not super worried. Just looking for some reassurance.

Title: Re: Any clues before you drop a valve?
Post by verslagen1 on 11/14/09 at 22:33:58

My theory on the dropped valve w/o the cam chain going are stuck valve guides. There been a couple that that's what it could've been.

Title: Re: Any clues before you drop a valve?
Post by BurnPgh on 11/14/09 at 22:46:20

hows that? If the valve were sticking in the guide would I not have some forwarning? Loss of power etc? I have no loss of power that I can tell. And how would that even come to be?

It's a bit late now and my bike is quite loud. I'll ride around the neighborhood tomorrow and see if I cant pinpoint it. Last time I had a funny noise it was a very simple fix (loose top engine mount). Here's hoping this is just a rerun.

Considering the valves dont ever meet the piston area on a stock engine the valve(s) would have to be left open for some time and burn up to the point of snapping, no?

Title: Re: Any clues before you drop a valve?
Post by verslagen1 on 11/14/09 at 23:38:55

The savage engine is an interference engine.
Which means if the valves are left open when the piston comes around... bang. And because of the angle they are at with respect of the piston, I don't think the piston will help them close.

Title: Re: Any clues before you drop a valve?
Post by Oldfeller on 11/15/09 at 03:26:05

Verslagen is correct, if your exhaust valve sticks in the up position it can catch a lick from the piston next time round.

The list has seen at least 4 reported busted off exhaust valves in the last 3-4 years. So, it can happen.

Now, chicken or egg discussion, what comes first, fracture of the valve stem at the base of the tulip, or contact with the piston? We dunno.

It seems to always be an exhaust valve. It tears things up terribly kicking around on the top of the piston, getting slammed between piston crown and head dome, generally scrapping out the head, piston and cylinder.

You don't want your valves to stick. Oil flow / pressure on our bikes runs at a minimal level, so any failure to get oil up to the head can cause bad things to happen. This is just one of them.

Putting a strong coating of ZDDP on your valve stems and guides can help bridge any interruption of oiling or short term overheating of things up in the head area.

As a list we keep stressing motorcycle grade OIL QUALITY as a major concern for wear items up in the head and for keeping your idle speed up over 1000 rpm to make sure your puny little oil pump is pumping enough oil pressure to get it up there.

===========

(has your bypass tube up on the head come off by any chance? It could make a new huff/whistle noise all by itself ... )

Title: Re: Any clues before you drop a valve?
Post by Charon on 11/15/09 at 06:18:46

I just KNEW there was a reason for liking two-stroke engines.

Title: Re: Any clues before you drop a valve?
Post by Routy on 11/17/09 at 04:50:39

But I'll bet you can't think of another one ! :o

Title: Re: Any clues before you drop a valve?
Post by Routy on 11/17/09 at 05:17:08

Till 6 months ago, I just knew a valve would never stick in a guide while it is running, especially at 1/2 throttle, light load, and in cool weather. Now I know better,......in that my 17 hp twin cyl Briggs dropped 1 cylinder,..... stuck an intake valve,.... under those exact conditions, and for NO apparent reason. No noise, no damage, just pulled the head freed up the valve(w-d) and back together, used hd gasket and all,...running fine ever since. But I now run a couple ozs of top oil in the gas.

So,.....if these engines had much of a history of valve sticking, I'd run just a touch of top oil, even if it was plain ole 30 wt. And on my Riding mower forum, most the guys there run top oil all the time, in engines that are heavily loaded in hot weather. It can really save an engine, and up the longivity of the top end combustion area by a bunch.

Title: Re: Any clues before you drop a valve?
Post by Charon on 11/17/09 at 09:31:41

I have had three valves "stick" on me. Two, while the engine was stopped, one with the engine running. First was a Honda Twinstar, on which one valve stuck open after the machine had sat for some time. When I started the engine the piston hit the open valve and bent the stem, so the valve did not seal and the engine ran on one cylinder. The valve did not break off, and did not damage the piston. Next was a Sears mower with their "Eager-1" engine. The intake valve stuck open and the engine would not start. I removed the head, turned the crank until I was sure the valve should be closed, then lightly smote it with a rubber mallet to free it. That was nearly twenty years ago and the engine still runs. Third, most frightening, was an airplane engine in flight. I had climbed to about 4500 AGL when the engine started running rough. Fiddling with the usual controls didn't help. The engine was still developing power, but not very much. It stretched my glide to the airport. Later the mechanic told me a valve had stuck.

Title: Re: Any clues before you drop a valve?
Post by bill67 on 11/17/09 at 09:34:52

Put some Sea Foam in the oil and you want have sticking valves.

Title: Re: Any clues before you drop a valve?
Post by Charon on 11/17/09 at 15:45:59

Hey Bill, do you use Sea Foam in your Klotz Racing Oil?

Title: Re: Any clues before you drop a valve?
Post by bill67 on 11/17/09 at 15:58:41

Not in Klotz racing oil,but all other oils,It frees your rings and cleans the engine,With Klotz you don't need it.