900 SS - Are Oversized Valves Available?
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I think my valves are sunk about as low as possible and I was thinking I’d prefer to install larger valves vs new seats. I try to use things like this to force me to make a performance upgrade. Besides , if I replaced the seats I’d have to match them to the ports. Also, I’d rather not deal with having the seats done. Just overall feels like getting bigger valves seems like less trouble and chance of something going wrong.
you can't go too much bigger without valve to valve interference issues - 1mm over on the inlet and std exhaust is what i usually run. to run larger valves you'll need to sink them, and then you head to needing to lower the collet groove and shorten the valves to not give shim range issues.
I guess the thing is IF I could get larger head diameters on both intake and exhaust it’s pretty easy to reduce the head diameters to get rid of the sunken condition and those kinds of modifications are available easier for me than seat replacement. I just don’t know who I wouldn’t trust locally.
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I have an ST2 motor with Kämna heads and +1/+2 ex/in valves. Extremely tight betrween valves on overlap, acc to Kämna min acc clearance on a 2V motor is 0.5 mm.
I don't know if the valves are sunk in the head. Afaik Kämna sells the valves, I bought +1mm inlets for my M800 recently.
I don't know if the valves are sunk in the head. Afaik Kämna sells the valves, I bought +1mm inlets for my M800 recently.
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The ones I bought from Kämna had both a lower collet groove and a longer overall length so gave shim issues.. I am waiting for thinner closer shims now, so maybe when the seats etc is done it will be different.
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duc96cr
What shim sizes are you at now?
It is not that common on street motors to have this issue, did someone in the bikes past cut the seats too deep? hard to say on a used bike but I do not see this often enough I stock the valves and work on plenty over the years. Make sure you need to do this before heading down the rabbit hole, do NOT expect much if any performance gains from just changing the valves.
If you are building your trophy 900 and simply want to play then have at it and enjoy yourself, that's why we some times do things. On the other hand if you are not hunting for extra power or a place to simply spend money you will want to have them thoroughly inspected to verify you are not just doing this for the fun of it. Also by the time you spend $$ on 4 valves, probably 4 guides, 4 seat cuts you may want to consider selling your heads and buying another set of used heads rather than changing seats. Again It is not common to need to do this.
What shim sizes are you at now?
It is not that common on street motors to have this issue, did someone in the bikes past cut the seats too deep? hard to say on a used bike but I do not see this often enough I stock the valves and work on plenty over the years. Make sure you need to do this before heading down the rabbit hole, do NOT expect much if any performance gains from just changing the valves.
If you are building your trophy 900 and simply want to play then have at it and enjoy yourself, that's why we some times do things. On the other hand if you are not hunting for extra power or a place to simply spend money you will want to have them thoroughly inspected to verify you are not just doing this for the fun of it. Also by the time you spend $$ on 4 valves, probably 4 guides, 4 seat cuts you may want to consider selling your heads and buying another set of used heads rather than changing seats. Again It is not common to need to do this.
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I´m just now working on the valve clearances, shim sizes mid-process:
On the M800, with +1 mm inlets from Kämna, I have the following:
Closers: 6.73 / 6.95.
Openers: 4.57 / 4.71.
On the ST2:
Closers: 6.45 / 7.39 / 6.70 / 7.14 / 6.70.
Openers: 3.22 / 4.18 / 3.01 / 4.43.
Very conviniently I have access to a small flat grinder, so I try to find a (closer) shim that´s slightly too thick, and grind to size. In my experience, especially with collets, it´s not very practical to go by sizes alone, as shims with the same measured thickness can give uite different clearances.
So far, I´ve not run out of "thicker" closers to start with.
Valve clearance on overlap:
DSC_1296 by torbjörn bergström, on Flickr
On the M800, with +1 mm inlets from Kämna, I have the following:
Closers: 6.73 / 6.95.
Openers: 4.57 / 4.71.
On the ST2:
Closers: 6.45 / 7.39 / 6.70 / 7.14 / 6.70.
Openers: 3.22 / 4.18 / 3.01 / 4.43.
Very conviniently I have access to a small flat grinder, so I try to find a (closer) shim that´s slightly too thick, and grind to size. In my experience, especially with collets, it´s not very practical to go by sizes alone, as shims with the same measured thickness can give uite different clearances.
So far, I´ve not run out of "thicker" closers to start with.
Valve clearance on overlap:
DSC_1296 by torbjörn bergström, on FlickrThe valves looked sunken before I disassembled the head. I don’t actually remember this but it’s in my notes from then. The seats were easily the worst I had ever seen, referring to the area that transitions into the port . They had multiple grooves in the throat surface and were smaller than the actual ports behind them . I smoothed them out. I lapped the valves, they seem to have a good, though narrow, seat. Because of the depth of the seat, cutting a wider seat would only lower the valves into the port. I really think they were replacement seats, done incorrectly, but I have no way of knowing.
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I posted a question on a FB porting forum about that ridge in the seat insert, just upstream of the seat. A 600 superstock (4 cyl) racer / tuner responded that it's for helping with the wet flow and worth several hp on their 600.
At least all the old-style 2V Ducs seem to have them.
At least all the old-style 2V Ducs seem to have them.
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I would install the valves to get a shim size first, then if you are pushing the size limits consider changing. Check openers too to see how thin they are, you could simply measure and post them up. Often there is plenty of material to cut seats numerous times as long as someone has not chosen your heads to learn on.
Stock seats and how they were blended were often a little less than beautiful, but they functioned fine for street riders. Could they be improved? Most times but then you some times ended up doing extensive work to the heads and that was often not cost effective.
Stock seats and how they were blended were often a little less than beautiful, but they functioned fine for street riders. Could they be improved? Most times but then you some times ended up doing extensive work to the heads and that was often not cost effective.
The seating area on the valve is on the very outer edge, and the seats in the head are narrower than they should be but there is no material left and I chose to leave them like that vs cutting them. They lap in fine , but the valve sits deeper than it should. The heads are off right now , so I figured now is the time to ask questions. The shims were nothing out of the ordinary so whatever was done in the past was compensated for. I blended the seat into the port but the sunken valve situation was already in existence. I just can’t see buying another set of heads.
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