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TR2/3/3A Installing PCV system on TR3

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martx-5

martx-5

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Getting ready to do the engine on the TR3 resto project. I want to put on a PCV system. I know, why complicate things. Well, I feel that a PCV system can only benefit the long term running of the engine and will lessen the oil seepage.

Anyway, I've gotten a hold of a valve cover with the snoot for the hose coming out the side as used on the later TR4's, and also acquired an intake manifold that has the bosses on the center log so I can drill and tap.

Has anyone out there done this modification? What do I have to do with the road draft tube?? What generic PCV valve will work?? And does anyone have a hose routing diagram or can link me to one??

Edit: BTW, I love the way the "preview post" works in this new forum. It just pops right below what you're doing. It makes editing a breeze. Thanks Basil. This is great.
 
Hi Art,

I'm putting a closed engine breathing system on my TR4, too. However, probably with some different challenges from you (because I'm running Weber carbs).

What Triumph did on the later engines is simply plug up the tube down on the LH side of the block. You can get the correct plug as used on TR4A from all the various vendors. It just taps into place. The venting from the top (valve cover) only should normally be adequate. However I wanted to maintain a crankcase vent as well... so modified the plug with a pipe coming out of it and will route a hose to a tee, or directly to a catch tank.

Triumph also changed the oil filler cap on those later cars with PCV. It needs to have a very small vent hole in it, not the large vent of the earlier cars. Depending upon what later valve cover you got, this might or might not be the type cap you got.

Later TR4 did not have a PCV per se. Instead they used a "flame trap" and had two hoses connected to the air cleaners near the throat of the carbs.

I think during TR4A era this became more of a true PCV arrangement, and tied to a vacuum on the manifold balance tube (something that can't be done with Weber sidedraft carbs, which is one of the reasons I need to take another approach).

The most important consideration for crankcase ventilation is to create a little bit of a vacuum inside the engine. This helps the piston rings seal better and helps prevent oil leaks at various places around the engine. It doesn't need to be a lot of vacuum, but needs to avoid any pressure buildup. A fully sealed up engine would build pressure due to the pistons moving up and down, and that would lead to leaks at the sump pan, rear main seal, front engine cover seal and would likely push oil up past the rings or down through the valve guides into the combustion chamber. In other words, a poorly vented engine will consume oil and drip.

At the same time, the source of vacuum can't be too strong, or it might suck up too much oil mist out of the crankaces and route that into the combusition chamber. The amount of vacuum is somewhat controlled by the small vent in the filler cap.

In a nutshell, if you were to install the crankcase ventilation from a late TR4A, that would probably be the easiest and best way to set up your car, assuming you are running SU carbs. You might want to consider keeping a tube coming off the crankcase, as well, and using a hose up to a tee, then up to the PCV valve. That will insure both the top and bottom of the engine see slight vacuum.

(Note: An alternative if you happen to be running an electric fuel pump with the original fuel pump blocked off, is to install a breather pipe in the blanking plate used there. Then, just plug the draft tube hole entirely.)

Cheers!
 
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