LO206 spring pressure

Freezeman

Freezeman

Site Supporter
I have been seeing a few cam failures with our group of LO206's. I also have directed my attention towards the spring pressures as a possibility of the problem.
My collection of old heads and springs include springs from 8# to 18#s @ .810 installed ht.
I don't have any newer untouched heads to check.
What spring pressure and at what height are you seeing new motors that don't fail come with?
Or what do you use as the least amount of pressure with the 6100 rev limiter?
 
All of the cam failures I've seen so far could be traced directly to oil or oil related problems. No proper break in, mixing brands or types of oil or, lack of timely changes. I've heard about some "soft" cams but haven't seen any. This is from engines where I have opened them up,sent oil out for analysis and done a physical inspection of the parts in question.If there is an oil related problem, fiddling with spring pressures isn't going to help.
 
Thanks Steve, I do agree with your statement of illuminating oil related problems. Even with a good oil regiment Briggs does have a warning statement about the use of too much spring pressure in their instructions. I am just trying to establish what exactly is too much or too little spring pressure.
 
With all the talk of cam failures I've had one that was on a new engine 2 years ago after replacing the short block and a proper brake in procedures ( 2 -30 min sessions with a good 30 weight oil ( Pennzoil ) we have raced this engine over 40 races with out failure . Today I decided to touch up the valves in the process I profiled the cam and checked the lift. .255 on the intake and .256 on the exhaust. Everything was with in 1 to 2 degrees and .001 lift based on my builder sheet. I've used the Amsoil Briggs 4 t from day one . With a new oil change be for the Main every race day. 17 wins and 22podiums with this engine . As you can see it has been worked hard .
 
I too see that most all the LO206 motors don't have any cam failure problems. That makes it a little harder to figure out what the problem was with the ones that do fail. The things that I see in common with most failures is that it happens fast. Generally with a new motor or new head and often coupled with questionable oil usage.
 
I have a number of 206s out on the track I've had only one failure as mentioned above I think it's lack of proper brake in and not running the proper quality oil as specified .
 
Most flat tappet cam failures can be traced to lifters not rotating and that said if one uses the wrong oil and runs a new engine at idle too long it is quite possible to have a cam failure right out of the box. The lifter to bore clearance is quite tight and if that lifter does not see rpm right away then the load on one point of the cam is substantial. Never seen one go flat later in life--- always right when in the break in process seen about five or six at our track. We have a huge field of 206's though so that # would likely be half or less at most tracks as we had 40 at our last club race. My break in procedure for all Briggs motors has been run it hard from first flash up never had a problem and i have built some fast motors over the years with no issues during break in doing it this way.

Greg
 
Thanks Elmer and Greg, Good points made. I do remember back when the animal first came out and I had three cams go flat in a row. That got me and others to polishing and clearance the lifters and bores. Of coarse we don't have that option with the LO206. Also I think a couple of failures may have been from the use of a break in machine that spins them at a steady state. I used to do that with my flatheads then changed to using more of Gregs method. I don't like the idea of using a different oil during break in.
Our group of LO206 racers is at about 50 which includes kids and adult classes. I don't service all the racers as I am not a Briggs dealer, yet I do seem to hear and sometimes help with all of their problems. LOL I probably have 6-7 wiped out cams and short blocks. Recently I purchased 2 new old stock 2012 short blocks to put into service and had a poor looking 2nd oil change on the first one. I measured the lift it was still fine with good leak down. I guess I'll just have to run it some more to see what happens. That block did show a little bit of an angled pop up so maybe it has a cylinder,rod, crank alignment issue? I set it up with 13 pound seat pressure. Should I go lower on the seat pressure? I used to put 8 pound springs in the 4100 rpm limited motors, that IMO is too low for the 6100 limiter.
 
If I were diagnosing an engine with a wiped out cam, the first thing I would look for is aftermarket valve springs. These engines are not designed for high spring pressure. If you put high rate springs in the engine, the cam is going to fail. If you leave it stock, you can beat the hell out of it and it'll keep running. As long as you have the correct oil, you'll be fine. I would recommend changing oil at the end of every race day but I know of a driver who hasn't changed his oil in over a year(4T OIL) and his engine is still as strong as any LO206 out there. I know every so often there will be an engine that will have issues. In my case I have seen a hell of a lot of laps put on LO206's and I haven't yet seen one cam failure. When I come on this sight it seems as if there is an epidemic of cam failures.
 
You must log in or register to reply here.
Back
Top