TR4/4A Valves and Guides

[KVH]

I thought my cylinder head was good, but the shop called to say the valves are sloppy in the guides, and are ground excessively from prior working.

The shop boss is about 70 and has been doing this kind of work since a teenager. I love meeting old timers who know their stuff.

Anyway, should I just get cast iron stock guides or do I go for manganese bronze? The shop says cast iron should be good enough.

As for the valves, should I go for stellite exhaust valves and standard on the intakes, all stainless steel? All 5/16 it appears.

The Moss catalogue is confusing me with all the reference to oversizing. The shop doubts anything I had was oversized.

 

[JerryVV]

Cast Iron, many shops don't allow enough clearance for bronze guides and end up sticking valves in the guide. It then can get expensive if the piston happens to hit the stuck valve. I know of several instances where this happened to street cars as well as race cars.

 

[TomMull]

Cast Iron, many shops don't allow enough clearance for bronze guides and end up sticking valves in the guide. It then can get expensive if the piston happens to hit the stuck valve. I know of several instances where this happened to street cars as well as race cars.

Got the same advice from my machinist, although without the rationale for not using the bronze guides. He used stellite exhaust too and hardened seats.
Tom

 

[Geo Hahn]

In my case too (2X) the choice was cast iron for the reason noted. I do not recall what valves I selected, probably stock. I went with hardened seats and, of course, new springs.

 

[sp53]

same as Geo

 

[Rut]

On my last rebuild I used bronze liners inside the original iron guides...no clearance issues, but all the benefits of bronze. Some shops charge less for liners than guides, but not much.
Rut

 

[CJD]

If you are replacing the guides, then you do not want oversized valves. In the Triumph world, oversize refers to the stem size...I.e for a quick rebuild you can ream the guides oversize and then use valves with oversize stems. I know this can be confusing, as I came from the Chevy/Ford world, where oversize valves referred to the head size. The TR4 head is too tight for oversize heads...but not oversize stems. You will want std guides and std valve stems.

Stellite is much harder, so it eliminates the chance of the tip mushrooming from contact with the rocker arm. Unfortunately, they want more for one stellite valve than for an entire set of std stainless. On my build it was not warranted...stock springs and street use. For heavy springs and high RPM, I'd recommend stellite...as the factory did in later cars for reliability.

Bronze guides are better if you plan to go to some springs with crazy seat pressures. I don't think it is warranted for any reasonable springs near stock. If you spin these motors fast enough to need crazy springs, then your crank will be the weak link.

Finally, these motors are not in danger of The valves contacting the pistons when using stock cams and rockers. If you increase lift or rocker ratio, then it could become a factor. The good thing is that the valves move parallel to the piston, so much less chance of damage if the valves did float from over-revving. It's a pretty bullet proof little motor.

 

[TR3driver]

If you are replacing the guides, then you do not want oversized valves. In the Triumph world, oversize refers to the stem size...

Sorry, John, but that is simply incorrect. The "oversize" valves sold by Moss and others have oversize heads, not oversize stems. For example, Moss 821-045 is an exhaust valve with a 1.42" head rather than the stock 1.3" head. Moss 821-035 is an intake valve with a 1.605" head rather than the stock 1.56" head.

They are useful primarily when you are trying to save valve seats that have been ground too many times without losing performance. The larger heads will sit higher, for better flow. Of course racers are apt to fit the larger valves anyway, but from what I've heard the performance gain is practically nil if the seats aren't "pocketed" into the head.

Much of the confusion arises because two different exhaust valves were used, with different stem diameters. TR2-early TR4 had 3/8" exhaust valve stems; while later engines had 5/16" exhaust stems. The earlier cylinder head was actually machined with larger holes to accommodate the larger exhaust guides.

But, as the Moss catalog notes, cylinder heads are frequently swapped around, so it's not unusual to find early engines with small stems and/or late engines with large stems.

In addition to that, the factory offered "conversion" guides, to allow fitting the later 5/16 exhaust valves to the earlier cylinder heads with the larger holes. These guides were originally in cast iron, but when I ordered them from TRF recently, I got bronze guides instead. Moss lists the cast iron conversion guides, but when I called, I was told there were out of stock with no estimated arrival date.

Since IMO the smaller stems do offer some performance advantage, as well as making the valves last longer, this is the one case where I would recommend bronze guides (and will be using them on my own rebuild). But I'll still use cast iron for the intakes.

As noted above, the bronze exhaust guides need to be reamed larger after installation, as the clearance will close up more in operation than with cast iron guides. Having a valve stick on a TR motor is not necessarily a total disaster, but certainly can be. The valve doesn't hit the piston, but the pushrod can jump off the ball of the adjuster pin and jam the edge of the pushrod cup against the ball. The resulting damage can ruin your whole day

 

[CJD]

OK, there are oversize heads available. IMHO, they are still not worth considering, and here is why...



This is a typical head with worn out seats. Normally the exhaust valve, on the left, would be sitting even higher than the intake is sitting. It has eroded a pocket down into the seat, with a space around the head about the same as the worn out valve guide clearance...or several thousandths larger than the actual head.

For a Chevy, the exhaust valve is 1.6", with oversize of 1.88". That leaves .28" to carve a new valve seat around the worn pocket, and the resulting seat looks like new. There is also a noticeable difference in area to increase flow. This is a machining procedure that makes sense...like new seat with more flow.

The Triumph oversize head takes you from 1.3" to 1.42". That only leaves .12" to work with when cutting a larger seat. In the head above, the width of the seat will be marginal, and there will be a ridge left under the seat that does not help flow. So, you get very little extra area for flow and a narrow seat with a ridge that will wear faster.

The intake situation is even worse...1.56" to 1.605" oversize...or .045" to work with.

The question is then, why not use even larger heads than 1.42 and 1.605"? You start to run into clearance and flow shrouding problems with the side of the chambers, and the room available between the valves themselves. In short, your running out of room...

 

[TR3driver]

Agreed, the oversize valves will not save a head with significant seat erosion (aka recession). With unleaded fuel, no doubt such damage is more common. But "back when", the initial problem would usually be only slight pocketing, caused by grinding the seats. That's the problem that the oversize valves were intended to solve; not valve seat recession.

 

[Simon TR4a]

On my TR4a I have bronze guides, I thought they were silica bronze but possibly are manganese bronze, with hardened valve seats and oversize valves.
It is quite correct that the valve stems come in two different diameters, I think the older heads had thicker valve stems, mine are the thinner stems but larger valve heads, from Triumphtune. I have a Kent cam with 290 degree duration and .310 lift, and the head has had a lot of material removed to unshroud the valves (removing the ridge John mentioned) and plenty of skimming done to increase compression ratio. I had to use .100 thou shorter pushrods to restore the correct valve geometry as so much was skimmed of the head.

The previous cylinder head I built used standard size valves, also from Triumphtune, again with hardened seats and bronze guides, and the dyno did not show any improvement with the bigger valves, which was disappointing, so I would not bother with that.