Jake Brake Circuit Breaker Size?

[chessie4905]

You could put the piston on tdc and manually depress each valve in that cylinder to see how far down they will go till they contact piston. Then you"d get an idea how much margin you have after subtracting minimum allowable piston to valve clearance. Same thing is done when building race engines, albeit in a slightly different way with spring removed and after final cam timing is set.

[bevans6]

You could do that, the info I found is that the injection event starts a 19.5 degrees BTDC and ends 5 degrees BTDC.  That is variable based on what the profile of the cam lobe is and what injector height you set your injectors to - 1.460 is more advanced than 1.484.  Jake timing isn't dependent on injector heights, of course, just on the cam lobe timing.  Advanced timing on the cam would advance the Jake brake event, probably reducing it's effectiveness just slightly.

[Geoff]

You could do that, the info I found is that the injection event starts a 19.5 degrees BTDC and ends 5 degrees BTDC.  That is variable based on what the profile of the cam lobe is and what injector height you set your injectors to - 1.460 is more advanced than 1.484.  Jake timing isn't dependent on injector heights, of course, just on the cam lobe timing.  Advanced timing on the cam would advance the Jake brake event, probably reducing it's effectiveness just slightly.

If you reduce the Jake clearances the 2 exhaust valves they control would open sooner and be held open longer.  Personal experience is they work better as an engine brake with tighter clearances.  Having worked for Detroit Diesel in the heyday of the 71-92 series, I worked on many trucks and a lot of them had the Jake clearaces tight.  If I worked on one with the Jakes tight, you could really tell the difference on how they shuddered the engine down to an idle. I would just leave the Jake adjustment like it was to keep the driver happy.

I never saw an engine failure from tight Jakes.  I have mine set at .035 and they work great. .040 might be "safer", but I don't know from what.  The piston isn't going to hit the valves from my experience.  But don't blame me if you are DIY and make a mistake.  I have certificates from DD to work on the old 2-strokes, before DDEC and smogged engines.

Geoff

[richard5933]

This thread is getting mighty technical. Lots of good information, for sure, but I'm am glad that I've got a tech with 40+ years experience working on DD 2-strokes set to do the work. Since things inside the engine are not my strength, I'm going to let him do what needs to be done.

I'm just glad that i was able to get the prep work done and save at least a few hours shop time.

[luvrbus]

Let us know what your guy sets the Jakes on Richard,I have seen the valves hit the pistons,depending on the cams and pistons clearance will change,you change the valves springs and seals on a 2 stroke by just rolling the piston up to TDC so they are close on clearance .Geoff built his engine and knows what cams and pistons he has,the average person has no idea what he or she has inside the engine   

[richard5933]

Let us know what your guy sets the Jakes on Richard,I have seen the valves hit the pistons,depending on the cams and pistons clearance will change,you change the valves springs and seals on a 2 stroke by just rolling the piston up to TDC so they are close on clearance .Geoff built his engine and knows what cams and pistons he has,the average person has no idea what he or she has inside the engine

Since my engine has less than 50,000 miles, I'm going to assume that the valves are original and still have the factory settings. I'll talk to the guy before he does the work to see what he says.

Is there a way for him to verify current setup and proper settings from inside he valve covers?

[luvrbus]

I doubt your guy is going to want to go to that much trouble,he is going to be a little on the cranky side anyways installing the Jakes on the upper head  the old 71's didn't have all the options the 92 series did 

[Geoff]

The mechanic installing the Jakes can check the settings and they are right he doesn't have to change them, saving time.

I have a 6V92 I'm going to be working on that will give me time to check the piston to valve clearances and Jake brake clearances.

[luvrbus]

The mechanic installing the Jakes can check the settings and they are right he doesn't have to change them, saving time.

I have a 6V92 I'm going to be working on that will give me time to check the piston to valve clearances and Jake brake clearances.

I have a head sitting on two pistons I am going to check the clearance at TDC just for my own piece of mind.I am going to measure it with 17:1 and 19:1 pistons I know there is 0.40 difference in the dome on a N/A piston vs a turbo piston.  I did check a DDEC cam and it has a higher lift than a US cam from a 8v92,now i need to dig around and find me a CA cam and measure the lift on it
   

[chessie4905]

  thanks guys!