Britbike forum Forums British Motorcycle specific Brands Triumph bulletin board oversized valves fix deep seats?

anybody got a success story where aftermarket oversized valves have brought back to life a head where the seats were too worn to install stock sized valves? I found a T 140v single carb head but it looks in very questionable shape--- ie- deep pocketed and nicked up seats-- gasket surface and combustion chamber nicked up-- guides probably bad also-- without the head in my hands is there a way to measure if oversized valves will " go get" unused seat surface? I know these heads are getting rare so I'm seeing if this head can be brought back. thanks, Bob

My Trident had badly sunken valve seats as a result of the ignorant mechanic that worked on it (which would be me). I used oversize valves and they helped for 5-10 thousand miles. Ultimately, however, I bought another head and sent it to Ed V to do his magic on. One thing about using the oversize valves that I recall. Valve guides are not necessarily perfectly Concentric with the valve seats. You are going to have to verify that the oversize valves are actually touching and creating a seal all the way around.

Ed from NJ

Lots of automotive valves available in 5/16" stem that can be adapted. Many are black oxide coated and less than $10.
Manley makes many 5/16" stem valves with various head diameters. These probably need the head diameter modified.
Of course you have to shorten them and recut the keeper groove.
New valve seats can be put in also but more expensive.

What you will need to determine is wether or not fitting and recutting oversize valves will bring the valve stem protrusion to within spec. You do not want to do this with worn guides so worth replacing with good quality ( not Wassell ) modern guides.

Rod

On a side note, LF Harris is now making new heads for TR7RV motors. They are the late version. Have screw in exhaust ports/spigots. Come complete, or bare. No idea of the quality, but in my area TR7 heads are very, very rare in my area. Junk ones can be found.

Bonneville shop & a few others sell them.
Don

If you want to be confident of how the engine will behave, get new valve seats or seat inserts, at standard size.

You may be of a “tuning up” or experimenting mind, in which case you’ll go for bigger valves.

"A T140v single carb head" is in actual fact not that, it's a TR7 head, but we all know what you mean. The smaller ports are a boon, do NOT go bigger!
First I'd like to know how deeply recessed the valve seats are. It usually looks worse than it is. Up to 2 mm or .080" is tolerable. If there's an edge from the cutting tool it needs to be blended in, especially on the inlet. The closer it is to the valve, the more important.
Not nearly as important on the exhaust. I've made up some simple tools on a drill to do this, but it can be done by hand. Stick an old valve in there to protect the seat and use a Dremel if you feel confident.
Your valve springs may need spacing/shimming under the spring seat to regain lost seat pressure.

The valve train geometry will be slightly altered but in the case of these engines it's not detrimental. I've done it with no obvious issues even in the long run.
PeteR (RIP) actually claimed sunken valves could be better. (His posts are still to be found on this site, bless him.)

I've used oversize valves to reclaim both inlet and exhaust seats. There are two important things too look for if you do this:
Make sure the valves don't sit too low, if the valve stem protrudes too little on the spring side, the springs may become coil bound. Not good.
You will also need to pay attention to your valve timing so they don't collide on overlap, especially if both valves are oversize.

Nicks and scratches in the combustion chambers aren't very important unless really bad. They will be smoothed out by carbon build up very quickly. To polish the sharpest nicks and edges, I use a soft stainless steel rotating wire brush on a drill. This leaves a very nice surface with any sharp edges eased down.
To restore the gasket surface I glue emery paper on a glass plate and run the head over it to flatten any protrusions. No need to overdo this, or you'll run into trouble with the push rod tubes later. Some kind of sealer can be used if the surface still has a lot of nicks and scratches.
NB! Chances are your cylinder head will be slightly bowed, in which case it may need to be straightened to be able to restore the gasket surface. Or not:
Deft hands and some emery paper may be all you need, carefully smooth down what you can and use the head as it is, with a careful re-torque regime, all will be fine.

This is my "fisherman's approach" anyway, akin to a Hillbilly , we had to make due with what we had. I found out decades ago that these old things can take a beating...

My 650 race bike has oversize intakes not for performance but for getting the valve seat in a better location....On my Triumph dual engine bike :,the 1969 heads had the slightly recessed seats...There was no room for an oversize valve because the original cast in seats were off center and a large circumference valve, usually .060 on Triumph, would run off the seat insert and into the aluminum...

As TT says, oversize valves can affect performance..but for a rider who rides casually ,lugging the engine , lol, it would be unnoticed...

Going oversize on the inlets can (not saying always) play merry Hell with idling and low speed running!

i had MAP put in 3/32-inch OS valves in my morgo T120 around 30 years ago. they've worked very well with mild porting and 32 or 34mm VM carbs. idling and low speed are fine.

i don't know what the effect would be if you put in bigger valves and didn't change anything else.

Yes, I was just being sarcastic.....As you know.. LOL.....I had a 650 T120 Triumph in the past with .060 oversize intakes...I bike never seemed to run as well as it should... When I sent the race bike 650 head to Rob Hall for port work he seemed to be a bit concerned about the oversize intakes, a step in the wrong direction...Stock Triumph valve sizes are large compared to some more modern two valve bike engines of larger displacement making a lot more power...Left over from 1930's technology thinking...

They made the 650 valves bigger in 1964. Possibly (and perversely) because BSA was advertising their 650 as “Big Valve.”

thanks for the good info guys-- I'm going to see if the seller can give me some measurements on this TR7 head-- i.e.- seat depths-- gaskets surface flatness-- and guide condition--

Seldom do you buy a used Triumph head with guides not ready to be replaced.

rob hall is experimenting with us.

i have a late 72 9-1/2-bolt head, and he put oversize intake AND oversize exhausts in mine, plus filling and raising the ports. he wanted a late head, because he could go bigger in it, 33mm i think he said.

Back on track, I've had a look at the cylinder head in question and the exhaust valve seat in question is beyond repair, judging from the photo.
The combustion chamber looks bombed too, something bad has happened here and someone has tried to fix it by going mad with a cutter.
There isn't enough metal left to hold a new seat either. Making up a completely new seat would take a lot of work, including welding. It would easily become more expensive than a new head, available from around £600,- in England.

I've advised Bob to stay away.

I also saw the head and and agree with Stein Roger....

Very good advice guys-- stay away from the TR7 head on EBAY--I have a real good 79 T 140D head and have pretty much decided to run with that.

Notice the chamfer around the left chamber has been completely removed on the sides between the valve seats indicating the chamber has been ground out.
Must be new definition of "good" that I was not previously aware of.

Hi, Out of curiosity, is a conversion manifold made for a T140E straight port head to convert to single carb? Web search didn't readily show one. Lots to make TR6/TR7 heads to dual carbs, but not the other way.

Don

What are you all looking at? I've just looked back through all the posts in this thread and I can't see any photos or links to Ebay listings - how do people know what this head looks like?

Quite. Is this a private conversation on a public forum?

Using the information in Bob's first post, and a bit of imagination, it's not hard to find this:

https://www.ebay.co.uk/itm/Triumph-750-TR7-71-3779-Cylinder-Head-No-Broken-Fins-Nice/143099111404?hash=item21515f27ec:g:EZUAAOSw2~NcRgS6:rk:5:pf:0

Link to E Bay item.

Looks like scrap to me.