Unit 650 valve stem protrusion after cutting seats? Does anyone have a good spec for this?

This post contains a couple of references to businesses that should in no way be taken as advertising, I'm just giving due to good service and possibly sharing some good resources.

So after much aimless roaming and searching of the interwebs, (and an email to Franz and Grub Vintage Triumph motorcycle engine parts & machine work-Franz and Grubb , who was imminently helpful, shout out for that) I came across this. https://vintagebikemagazine.com/wp-content/uploads/2017/06/650-750head.pdf (It's a safe link, and if you have any interest at all you need to download and save it.) It's the closes thing to a definitive answer that I was able to find as far as what the protrusion should be, although it still doesn't address the issue of how much one can get away with, AKA service wear limits. That said, using this info I come to the conclusion that the exhaust are sunk over .100, and the intakes over .060, so I'm confident that seat renewal is in the future.

With that in mind, I started searching for seats. The original seats in these heads are reverse taper and cast into the head, and often are not perfectly aligned with the valve guide bore, so cutting them completely out takes extreme material removal. It seems most folks just cut into the existing inserts and press the new ones into them. I couldn't find any ready made seats that were exactly right for this application, so started searching for something close that I could make work. In my search I discovered a company called Tucker Valve Seat. (no title) The name is self explanatory, all they do is valve seats. They have an online catalog with a section that lists seats by OD, so I went through that and found some that were close to what I'd need. I called them and spoke to a very nice lady about their services, and she informed me that you are not limited to standard dimensions at all. She told me that you can cut your holes, measure them, and then call with the measurements of the seats that you need to fit the holes you have cut and they will make them to spec and ship them within a week. The size ranges I was talking to her about were quoted at under $15 dollars each. When doing valve seats in the past, using standard "universal" replacements, I've always sweated (and sometimes f'ed up) getting the bore and depth exactly right, this service removes all of that stress. It also removes the hassle of having to shave down a "universal" seat in . lathe to fit an oddball spot. Maybe everyone else knew about this already, but it's a game changer for me.

Now, if you'll excuse me, it's over 60 degrees out and I need to get a ride in.

Rick_Bee said:

I wonder if the valves were sunk purposely to allow more lift?
Why would someone bury them that deep?

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Sinking them to allow more lift wouldn't really accomplish anything. Any extra lift would be negated by the shrouding from having them so deep.



That's not even considering the fact that the valve train geometry is now completely out of whack, with the rockers pushing the valves sideways more than they should and wearing the guides. (The guides on these were worn oval already, front to rear in line with the rocker arms they would wiggle a lot, side to side hardly at all, which is a tell tale sign of bad geometry.) And that's IF the rocker arms don't hit the spring retainers and push them around causing the keepers to wear out.

As far as WHY someone would do that? The only reason I can think of is ignorance, as in they just don't know any better. The fact that there really isn't a clear go/no go spec for these like there is for almost every other engine I've ever worked on is telling. You can see that these have been cut multiple times, and in the absence of anything telling people not to, folks just keep going. I'm sure I could just put these back together and the engine would run OK for a while, but I don't like doing things that way. I've already done enough of that kind of stuff before I knew any better.

I'd bet I'm responsible for a few sets of Triumph heads cut way too deep!

When I was still learning to do engine work, I was in my 20s and lived in NYC. At that time there seemed to be a bunch of completely fucking beat Triumph rat bikes all over Brooklyn and the East Village. They were bodged together, rusted, dented from battles with taxi cabs, etc. You could buy them them all day for $500 to $1000. They were a great commuter option for many . . . tough enough to get the job done, not so precious you couldn't park them on sidewalk.

Background is key here. These bikes were largely considered worthless.

Combine that context with my still learning and not knowing fancy details such as ideal valve train dims/geom and I'd put new guides in, cut the seats with my NewWay cutters (I was so proud of myself!), installed new valves and put 'em back together. Seemed to work.

What I didn't know was how long they'd last. That the guides would be short lived. That the seat lift pressures were low and likely to float valves at high rpms. Etc.

The punk and hipster kids that rode these all over the five boroughs likely didn't know or GAF either.

Posts like this one above, have taught me a lot over the years . Thank you to those who have enlightened me, knowingly or unknowingly.

Jason

p.s. - not a Triumph, but an example of the type of Brit bikes that were laying all around the city

Just checked, it states that at mid lift adjuster ideally should be in line with the valve with contact point central to valve.
Seems like a no brainer when you think about it.
In consideration of after market valves where stem length can vary, it goes on to say, machine valve stem length down or too short, use valve caps.
Not too sure about that last one, additional noise or would oil 'stiction' keep them in place?. Also on Triumph the rocker box gasket thickness will possibly change everything when replaced.
Get Tuning For Speed, speed holes are the tip of the ice berg { anyone here remember Malcolm in the Ogri strip cartoon going over board with speed holes, maybe just an english thing for us oldies } you'll have hours of fun modding everything, if you don't have bench grinder, get one.

Thunderbird said:

Just checked, it states that at mid lift adjuster ideally should be in line with the valve with contact point central to valve.

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That is absolutely the goal of knowing the acceptable valve stem protrusion, specifically to get the contact points between stem and adjuster to meet properly. It's an easy thing to check and get right IF you have the numbers. I don't think just eyeballing it with the rocker box setting on the head is good enough, especially when dealing with things that have been knackered and bodged by countless others before. In order to get a really good view of it, one would have to cut apart the rocker box so that it could be checked from the side.

Thunderbird said:

In consideration of after market valves where stem length can vary, it goes on to say, machine valve stem length down or too short, use valve caps.

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Caps are perfectly acceptable as long as the valve stem has enough space above the keepers, some don't. In this case I'm using stock spec valves and returning the head to as close to new condition as possible.

Thunderbird said:

Also on Triumph the rocker box gasket thickness will possibly change everything when replaced.

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Absolutely. With the 45 degree angle of the valves, a very minor difference in thickness can be fairly significant when it translates to rocker/stem relationship. Unfortunately, one cannot just put a thicker gasket in to compensate for taller valve stems. The valve angle moves the tip of the stem away from the axis of the rocker as much as it does up.

I have access to a copy of tuning for speed, and many grinders (angle, straight, bench, pneumatic, electric, low speed, high speed....). These days though, I tend to build and tune for longevity and reliability. Guess I'm just getting old.