MGB: Dyno Runs

Well, we took another baby step toward getting the car sorted out.

Hap scheduled a dyno run for me at Top Dead Center Auto in Spartanburg, SC

As you followed, we had a less than stellar test day at CMP in July, though we solved those issues that only the track can reveal - tire rub.

So this time, we decided to take the less costly and lower involved dyno route to finish out the tuning process.

So, Kevin Hart and I met Hap this morning for the runs.

It was another mixed bag. We got the timing dialed in and the fuel to air mix is good. But the computer never captured any data from the runs, so no hp numbers, no torque numbers, etc.

But we discovered that there was a hidden issue with the rocker arm assembly that first revealed itself in Daytona. So, there is some work to do. We also saw some dangerously high water temps with no real explaination as to why.

I have some work and investigation to do. Here are two links to short videos of the runs.

http://vids.myspace.com/index.cfm?fuseaction=vids.individual&VideoID=40912549

http://vids.myspace.com/index.cfm?fuseaction=vids.individual&VideoID=40916394

And two pictures of the car on the rack and out front of TDC Auto.

I throw the rocker arm issue out there to the crowd for feedback. First a little history on Fred engine. Fred first bought his car as a street racer if you will, a cammed up street engine someone had built, when we converted fred to mare racier set up, still a bit tmaed by full ut race engine, but a good basis for fred to start racing we used the rocker arm assmeble as it came off the Street engine, someone had rebuilt it, new shaft everyhting fitting good. At Daytona fred got some backfiring on track and we discovered #5 rocker arm adjuster all the way up and and the nut lying there on the top of the head, we pulled the carbs check that pushrod for straightness, pulled that lifter, all looked good. I simply wrote this off as fred being kinda new to machinics not getting the nut tight, I also found another adjuster nut finger tight, Fred after firing the engine had to do a retorque and valve adjustment, so I just thought it was not completely tighten by him. The valve have since been adjusted by me twice, and I know I got it them tight, and sure enough #5 backed all the way off again, the threads on both the nut and adjuster look ok, so I'm thinking the threads in the rocker them self are a bit shallow, now mind you all this stuff turns just fine , nothing to lead you to believe that any of this stuff is stripped. At his point I'm a bit parnoid, and would like to go through the rocker arm assmebly miyself, but we don't have alot of time before the Barber race, I may just see if I can prepare a back up to take with me to Barber, and get Fred to switch out the rocker arm in question with a spare he has. The future pans for this engine will include carrillo ords, more compression ratio, and roller rockers, but for now we're just looking to get Fred's feet wet.

Any other stock rocker arm expereinces simular to this haunted you guys? I've neer had a roacker arm adjuster back off on me, stock or roller, and now it happen twice, so that tell em it wasn't fred but rather the art itself.

Aout all we accomlished on the dyno run was getting a A/F/R reading the young kid running the dyno, never even got a reading to do a HP/torque reading, and still wanted to charge Fred full price, needless to say I had to call his bluff on that, typical tuner type kid, a baby without a clue. I used a couple of dyno shop in Anderson, with great success, and had bveen to this dyno shop only time with a local Midget racer, we chose to go here because it saved Fred a extra 60 miles of driving, which with our rocker arm issues, didn't mean much anyway, but i doubt i will use these guys again. Like always whether it a good day at the the chassis dyno or not, you always learn something, and we did today as well, really if you think about a big rather something with the rocker arm, so we may didged a bullit by going to the dyno in tha regard.

The car ran a little funny on the ast couple of runs, and I'm sure now that was the loosening rocker arm, after we fixed that temporarly in the parking lot the engine rev without a load just fine. Also if tuner boy was correct, which I highly doubt he said the roller were set at 6000 pounds on the chassis dyno, the Mustang dynos I used are able to calibrate the roller/s for lesser weight cars. THis unit is a dynojet, and i was less than impresssed by the operator.

Hap,

I have had this happen with stock rockers, a couple of things come to mind to check. Threads stretching obviously, also ckeck the contact patch of the nut on the top of the rocker, make sure there isn't a high spot on that rocker in particular. I have also seen a stock rocker bend, can't remember if the nut backed off when that happened but I can see how it could.

Barry

Fred & Hap,

There should be enough thread that you could double nut the offending adjuster to keep the base nut from backing off.

Steve

I just spent an entire day rebuilding my rocker shaft due to #5 rocker. I had been chasing fuel problems, carb issues and finally became frustrated when the car would not fire again. Back firing a lot and sounded more out of time than fuel problems. Even though it is a difficult job under the blower, I went through a complete re-set of the distributor, static timing and nothing had changed. Finally looked at the rockers, and there was #5 way out of whack. Nut and adjuster were still tight, but when I went to adjust again noted a crack on the bottom of the rocker. Closer look and it was bent too.
Checked push rods and all straight ... checked compression and leak down ... everything still fine. No idea why or how this rocker failed, but didn't find any other problems. Re-built entire rocker assembly, fired right up, ran up to temp, and no other problems discovered. (except a blower seal and return line still dribbles)
Now I would love to find a dyno to get some tuning issues done, but the nearest is about 3 hours away. I also would need an intelligent operator that could actually recommend changes too. That is where I would fall short, as my method is still by the seat of my pants and old school observation. Check plug colour for lean or rich. I have lots of jets, plugs, and c14 fuel. So I could spend a day of travel for a couple hours of dyno time and not be sure of what I would learn ... or I can go one day early to the race track for the test day and tune as I always have. Plus I get track time, for a lessor cost, that a dyno can't provide.

Well a chassis dyno is a good thing if all goes right,and a bargain if you have one close to you, fiquire Fred and this weekend is only time I exceeded 1 hour getting things right, and normally it's $100-125, which is way cheaper than you can go to the track.

Steve, maybe a jam nut, but there's not alot of threads left, my concern is it's not just the adjuster bolt or the the nut, that it could be the threads in the rocker arm itself, which a double nut wouldn't fix, I thought about using a nylock, which would work fine in the engine, 1275 from the factory uses a nylock ar a rod nut, so nylon holds up fine in any temps you would ever get inside a engine.

The double nut was a "quick fix keep it running" idea, but there's an underlying problem that needs to be solved... a fractured adjuster or the pushrod side of the rocker.

Speedracer Wrote:

The thread count on the rocker hardware is 5/16-24, all the the hardware is original, pretty unique hardware,so kinda hard to use someth9ing from another application, I'm just guessing that all the use that the rocker adjustment hardware has seen over the years is worn the threads thinner. I'm kinda parnoid about even going hog wild with taps, on block, components and head when building a engine to chase threads, I clean and blow out everything, use oiled threads and test fit stuff, and if i run into a problem, then and only then would I run a tap in a threaded hole. Everytime you you thread a fastner in a threaded hole, you lssesning the thread thickness alittle, with a tap, you're lessensing it alot. When it comes to taps, I would also recommned avoiding the el cheapo, third world made sets, get something good like a Hanson set, just because quality control and actual sizing will alot better.

We're going to replace the offending rocker arm entirely, and play it safe.

I pulled the rocker arm assembly and the #5 rocker bushing was worn so bad, the oiling groove has dissappeared. So, with one week to go until the Barber SARRC, the drama continues :)

Whoever built that engine as a street unit, had built that rocker assembly or at minumum a new sahft, and went through everything, I check the assembly and it looked good, check all the rocker arm on the shaft and they were nice and tight, my guess is someone used a bushing that is inferior.

Now it's entirely possible the bushing never had any oil grooves in it to begin, it by means is absolutely warranted, good idea, yes, absoleutely needed, no. Was the rocker sloppy loose onthe shaft? If it was, then has became so in a very short period of time, meaning is there another one of those hiding in the woodpile? I've got a couple of used assemblies, I'll check them, maybe looking at the used assemblies you have is the answer for now, and using one in it as a whole assembly.

Bushings can be made out of different types of bronze, I have to make custom rod bushing for the 1275 rod to convert them to floating, and I use alloy 954 because of laod strength and tempature range, lord only know what these off the shlf bushing are made of.

Here's the punch line to all this, whether the bushing has worn out or not has nothing to do with the hardware loosening up.

Pushrods?

Rockers?

What are they?

Real MGs don't have those, do they?

:-)

The Twin Cam has it's own set of challenges, but it almost makes me feel good reading these rocker problem threads that this is one thing I don't have to deal with!

I think what we got, I know more in a few days is oddball hack rebuilding on the rocker assembly, another used rocker arm wouldn't slide ove the shaft, so I'm guessing that Fred has a ssembly that someone used some sort of oversized shaft on, pictures of the rocker arm themselve seem to indicate the orginal bushing have been reamed/honed to fit the larger OD shaft. MGB rocker arms are pretty dead solid relaible, so this is out of the norm. Fred getting a rebuilt set form Bob White tonight, and I got a couple of good used assemblies, so we should be fine.

There's a .005" oversized shaft available to put the worn out rockers on without having to rebush them. Sounds like that's what you had. That sucks! For all you know, someone could have knackered up a couple busihgns to make them feel tighter too. I've seen that in enough distributors - that and grease packing to make them feel tight until they're run and its all washed out. Good stuff!

I think the material they use for bushings is called toffee.

I hate the .005" shaft, its OK until you want to re-bush one rocker the day before a race meeting(when doing a head job)..... and then find the rocker shaft is OS.

Yeah, I got a refurbished unit and it too has the oversized shaft. Luckily I now have two oversized shaft "sets."

I got it all on and started up. I'll time the car again tomorrow so I can run it through a heat cycle and check the rockers for tightness etc.

I did not even know that there were oversize rocker shafts! Now i know how they can build them and sell them for the price they do. 15-20 years ago when i had my first shaft assembly rebuilt at a machine shop the price was more than i paid for the one Fred has now. I would wonder if a small piece of something plugged the oil hole and that wore the bushing. Still a mystery as to the nut backing off. I hope everything works out with that shaft assembly. It will be nice to get feedback on it. Bob

I've never seen a OS shaft for sale..... I guess they are avaliable on the trade market for specialists who will sell you a re-con rocker set... It saves them re-bushing, reaming and drilling 8 rocker arms.

Fred, Did you just remove the rocker ass, or un-torque the whole head???

I removed the entire rocker assembly. I loosened all 11 of the head bolts in sequence and then removed the assembly.

After picking up the unit from Bob, I got home and disassembled it, inspected it, sprayed it down with carb cleaner to make sure the oiling holes were not clogged, oiled it back up and assembled it.

Put it back on, tightened in sequence, torqued and adjusted the valves. She started right up and after a few start ups, everything seems to be in good shape.