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Old 04-20-2012, 05:11 PM   #141
adecritten
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Quote:
Originally Posted by mikef4uk View Post
3 bent valves? my money is on someone getting the cam timing wrong for some reason, could they have stuck open due to the motor sitting around maybe?
Mine was on a Beef Chop Suey for the same reason!!


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Old 04-20-2012, 07:02 PM   #142
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The bike was a real rat. Looked like it had been sitting outside for all of its 8 years. I would assume the 3400 miles is correct. The bike didn't look beat on, just neglected. Here is a picture of the bent valves.

One of the differences between SPR valves and stock 750 valves are the SPR valves are necked down after they leave the guides, and they are dished, like the exhaust valves. The stock 750 valves have a flat face on them.
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Old 04-20-2012, 08:32 PM   #143
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How about no oil in the head and the cam forcing down on a very hot, expanded and stuck valve. Or perhaps from overheating?
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Old 04-20-2012, 08:52 PM   #144
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Not sure, Chris. I suppose I'll never know.

I've seen plenty of bent valves in these engines and they always bend in the same place. Between the back of the seat and the guide. Exactly where you would expect. These three valves are so much bent as warped. If you expand the picture and look very closely you can see they are not sitting flat on the plate.
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Old 04-20-2012, 09:46 PM   #145
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Oh I got it now. The face is warped. Not the stem?
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Old 04-21-2012, 12:10 AM   #146
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If valves are going to stick open it will happen after the engine hasn't been cranked in a while, not straight after its been just running. Also if someone has fucked up the timing and torqued the cam caps down and pushed a valve on lobe into the piston it shouldn't run properly from startup. Plus only 1 cyl would have bent intake valves. Which 3 valves on which cylinders were the bent ones?
If it was caused by heat from valve adjustment you should see evidence on the seats, heat from detonation should kill exhaust valves first.
How badly were they sealing? No comp at all or was there a little bit in the affected cyls? I would have thought that valves only slightly warped like that wouldn't cause the engine to not start.
When u checked for fuel was the injector spray strong? Reason I ask is that if ur fuel feed line comes off intank ur injectors will still squirt fuel out from gravity acting on the higher tank. Not enough to start the bike though.
I really can't see how 3 intake valves would warp so badly as to cause no start from just moving the bike.
Maybe they have been like that for a while and arnt the cause of the non start issue?
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Old 04-21-2012, 06:04 AM   #147
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G,day Carl.

Put this problem to bed once and for all.

Get as set of " V " blocks and lay your valves in them and check the stems and valve faces for concentricity using a dial indicator.

then check the stems for size and then with a bore gauge check the guides. This is the only way , without sending your head into the shop , to have any certainty everything is o.k.

I would not put new or refurbished valves back into a non checked valve guide.

As a rule , if you use refurbished valves or use replacement valves they will need to be machined/reseated into the exisitng seats.

Just for the worth of mentioning it and not knowing other peoples degree of mechanical knowledge , if new guides are fitted the process of recutting/replacing the valve seat in the head must then be carried out.

each time the guide is fitted it will have a slightly different centre point compared to the previous guide.
If you were to drop a valve back in to this new guide the chances of it sealing up 100% is almost non existent.

Did I read somewhere in this thread this bike had recently come off the Dyno. If your valve springs are a little weak or the engine over revved then it may have got valve bounce. At 14,000 + rpm a little tap from the pistons on the valve face will be more than enough to bend the stem.

Last note , I think the evo2 and later , along with the SPR use a thinner valve stem . the idea behind this was to make the valve gear lighter giving better performance BUT there is a trade of...strength of the stems.

Good luck with your next stage.
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Old 04-21-2012, 07:53 AM   #148
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Quote:
Originally Posted by cdamb View Post
Oh I got it now. The face is warped. Not the stem?
Yes, the face is warped, the stems are not bent.

What it looks like is the back of the valve, the part that seals against the valve seat, is slightly peened over. So while the valve seals against the seat fine, this one area of perhaps 30 degrees out of 360 does not.

This is great information, Ken. I have a dial indicator and I will use that to measure concentricity of the valve stems and valve face today.
I don't know when they switched over to the valves with the thinner stems. I know the SPRs all had them, I know the Brutale 750s did not. The diameter of the stems seems within spec as do the valve guides.

Assail; from the beginning, when I first saw the bike there was something wrong with it. I ran rough off idle. The seller said he didn't know why. He said it pulled fine, it just didn't have that clean snap from idle. I had no idea what it was but figured that if the bike started and ran it couldn't be a huge problem. When I got the bike back here it ran like crap until I changed the chip that was in it. Then it ran fine until I tried to load it onto the truck for the trip to the dyno. That's where this thread started.

Yes, I said bent valves because that was the closest description I knew of. Is there such a thing as straight valve stems but warped face? Or peened over valve seating surface?

Perhaps a well nut got sucked in and got trapped between the valve and it's seat. Not bad enough to bend the valve, but bad enough to deform the surface of the valve where it meets the seat?

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Old 01-15-2013, 11:38 PM   #149
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Yes I know this is an older thread but as I am a new MV owner I have been reading through many posts and learning about MV's and specifically the SPR. I have read through this entire post and may be able to shed some light on the failure.

The valve failure you have experienced is known as "tuliping". It is more common than you think. I have seen it quite often in boats (I was a boat mechanic in a previous life). It results from the valve overheating and the hammering by the spring causes the valve head to deform and warp. When really bad it does look like a tulip. It occurs on intake valves too as they are often not of the same material as exhaust valves and will fail at a much lower temperature. Thin, lightweight valves are more prone to this.

As I mentioned the cause is that the valve got too hot. In boats this is generally caused by a lack of cooling water but running lean is a common cause as well as detonation from low octane fuel. Over-reving or sustained high rpm when running hot is a sure killer. Once it gets even a slight bit warped the valve is no longer in full contact with the valve seat and therefore is not cooled by the head and things go rapidly downhill from there.

My guess is that your valves failed from a lean condition or perhaps detonation. Since I cannot examine the parts closely I cannot tell if there are the signs of detonation or not. A small vacuum leak on one (or in this case two) cylinders is a common cause as is a partially clogged injector.

I hope this helps someone.
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Last edited by Cybeeria : 01-15-2013 at 11:40 PM. Reason: spelling! arrgh!
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