In looking at the sites for exhaust brakes, I see that heavier exhaust valve springs are recommended. I presume that the backpressure will open the valves when braking.

Will running without the heavier springs cause damage or will it simply reduce the braking force? Can a valve hit a piston?

Edwin

 

You will hit the pistons if you float the valves. You are correct on why the heavy valve springs are needed. If you want the exhaust brake to work to maximum effect, I would suggest getting springs for the intake as well. That way you can comfortably allow the RPM to rise above 3500. Remember that exhaust brakes are more effective the faster you spin the engine.

The BD brake and the PacBrake PXRB brake are more effective at low RPM than the others because they use a spring loaded flapper instead of a fixed orifice.

 

I assume by float the valves you are referring to overspeeding the engine where inertia causes the valves not to close fast enough. Wouldn't the backpressure tend to open the valve on the downstroke of the piston? Since the valves are straight on rather than angled would an actual collision be less harmful than otherwise?

How hard is it to install the heavier springs? Does the nead need to be removed or can you put compressed air in the injector hole to keep the valve closed?

Thanks

Edwin

 

The backpressure can float the valves at any point (OK, except on the compression stroke). It has more to do with the pressure inside the manifold than with RPM.

You don't want the valves hitting the pistons even if they hit straight. If you don't bend the valves (remember that there's a big bowl in the top of the piston) you'll nick the piston which is a good place to start a crack.

The springs are changed by allowing the valves to sit on the pistons at TDC. Not hard at all, no special tools other than a spring compressor.

 

Yeah, I just did the valvelash today, took a total of 1 hour but I didn't completely reassemble everything since I'm waiting on parts to install the WH1C turbo. I was pleasently surprised that the valve covers had such nice gaskets that didn't require changing. Looks like Cummins anticipated having to adjust the valves many times.

They weren't off much mostly were OK except a couple of exhaust valves were excessive play. The air-ratchet sure helps in disassembly.

 

Actually if you have the proper tool, doing the springs is fairly easy....
You might also want to consider putting in a new set of stem seals too ( I think they're available for 12V's)...they make a good high quality set that will not come dislodged....
The tool we use at the shop to do the springs is fairly basic...I don't know if it's a snap-on or not but it takes about 10 minutes per spring when you get into a good rythmn....(sp)

pb.....

 

OH,,,,,here's an FYI/heads up.....

Today we had a fellow come into the shop from a neighbouring province. Before he left home he checked his FP on his 24V....thought it was kinda low and didn't want to loose a VP44 so....he bought a pusher to help out.
It was an MSD (gasser??) pusher pump.....
(I'm guessing it was a gasser/race application pump) but....I'm thinking he was pushing some REAL SERIOUS PRESSURES cause shortly after he left on the trip to come into BC, he saw his 250 litre tidy tank needle bouncing all over.....
A few minutes later he looked again and he had lost some 50 litres of fuel....

Seems the pump pushed so hard it blew the oring seal on the fuel filter canister top AND cracked the high impact (abs?) plastic top too.
He got a new top and seal and installed it and was once again on his way....
Yup...you guessed it,....he manage to drift into the shop with fuel just screaming out from under the hood....did it again.

We pulled the pump and put in a Carter pusher for him since he was on his holidays with the Mrs.....
We finally got him all hooked up and on the road about 5:30 PM today, our mechanic stayed well past closing to make it all happen...


The moral of the story..... CHECK THE SPEC ON THE PUSHER PUMP YOU INSTALL CAUSE IT JUST MAY PUSH 100PSI +++ AND BLOW THINGS ALL TO RAT SCAT...!!!

pb.....

 

I read somewhere (here?) that there was no need for valve stem seals since there was usually positive pressure so it wouldn't suck oil. Guess that was wrong.

Anyway, thanks for the info. I like how everything is so out in the open and easy to get at. When I get ready to put on an exhaust brake I'll get the heavier springs. BTW, does, or how much does the heavier springs cause extra wear on the valve train, especially the cam. I remember on the old Chevy V-8's the cam was case hardened and once the it wore through the hard part the lobes went flat.

Funny story about the fuel pump.

Edwin

 

The seals aren't for preventing oil being "sucked" past the guides but rather to serve the function of preventing oil from running down the valve stem and into the guide. These seals will not become dislodged as can happen with stocker....at least that's my understanding and I'm willing to be corrected if I've characterized this incorrectly.

pb...

 

Once again bushy. It goes to show what service you provide at your company. GREAT SERVICE and that the mech that stayed late to help out a fellow CTD.