Best B20 engine valve choice?

1971_144GL

One for the B20 brains trust. @bigal is sending the crusher around for my collection on the 27th if I don't fix something. It would be a sad day to see the collection go. I spent two hours and have discovered that the lost compression on my 74 144 dual carb is due to a burnt valve (on left). For replacement I have the option of the same lighter thinner valve that sits recessed in the head, or the thicker heavier valve that sits proud in the seat. Possibly this type is sodium filled for cooling? Does anybody have any folklore on the best valve to choose. Does the large heavy, proud sitting valve get permanently hot and contribute to the pre-ignition problems these engines have? I am only tending to use the later larger valve heads on my B20's. Advice welcome, otherwise a good percentage of the early Volvo's in Tassie will have to visit China.

Vee_Que

It may be for the heads with valve seats, it won't make a huge difference honestly with a stock cam

Major Ledfoot

What type of head is it (B20A/B/E)? What is the valve diameter of the intakes and exhausts that you have?

I have a 73 164E head which has some good bigger (i.e. B20E) sized valves which you're welcome to.

30 years ago, I got excellent results with B20E valves in a B20B head which had some porting, reshaped and cc'ed chambers, plus a 3 angle valve job.

No B20 or B30 engine had sodium filled valves AFAIK - sodium filled valves on Volvo petrol engines didn't appear until the B21ET and FT in 1981.

1971_144GL

Thankyou both. The current head is a b20b from 1974 which is an injection head without the injector ports machined out. Pretty uncommon, but big valve, so theoretically desirable.

Just trying to get the car mobile again at present, so no performance consideration. I will do a full build down the track.

I have both types of valves handy, thankyou anyway.

The other reason for the question is that I am currently assembling parts for an engine build to get a 74 145 mobile. In this case I want to have a long term engine, so valve choice may be more important if the thin ones tend to burn? I have a choice of heads available, a couple of each type.

Spac

Very rare to hear of any OHV Volvo motor burning valves. I simply would not rate it as anything to worry about.

Massey165

The valves you use will have little impact on the engine performance, by far the most significant factor on getting the exhaust gas out of the cylinder is the large lump of cast iron that supports and protects the exhaust valve guide. machining out the roof of the exhaust port and installing a shortened valve guide with std valves will make a significant difference, 37 or bigger exhaust valve will go even

better. See attached

Vee_Que

That, but do not touch the bottom wall.

Major Ledfoot

I'd go for the thicker heavier valve that sits proud in the seat.

There were 42mm and 44mm valves as standard, and I wonder if the the thin one that sits way down as you describe is a 42mm valve.

Bought a car many years ago that had a cooked exhaust valve, which may have been due to a failure to set the lash properly, so I've seen it happen before.

1971_144GL

Finally some 142 time I hope. Thank you for the advice.

I am going to use the thicker 44 valves. Pretty sure I used them the last time I did a b20 head, but can not find the pictures. These are a surprisingly smooth engine (for a push-rod) when given some extra time to finish them.

Vee_Que

Don't tell us you've made the port longer towards the head surface!? They are known to lose power from that.

1971_144GL

Yes I did. Still questioning that decision. I wanted a very smooth, rev to the red line with no drama engine, with no pre ignition. And that is more or less what I got. It takes any punishment, sits on 110 km/hr with ease, reaches 100 mph, and is well suited to the m41. The port and combustion chamber were altered toward this objective, and the result was a success.

But yes, I sometimes question the compression loss and power loss of the build. But not every build is about power. The next build will not include the same reliability priority, as I still have the curiosity of building an engine for power. That said, I would do this again to a head if I wanted long term smooth reliability and at least the same performance as a factory engine (just refined).

Vee_Que

Not asking about the combustion chamber. Just in the exhaust port itself. It's easy to find info online on what works for gaining torque and power on a b20 and most motors by lifting the exhaust port rather than lowering the exhaust extractor side hole.

robv

there is good power gains from un-shrouding the valves, obviously the bigger the bore the more you can re leave