0300 Rockers - Fresh Overhaul

[9976AJds]

Gentlemen, my IA says we must replace the drilled Exhaust type rockers (I have all 12 drilled, since 1984, 900 hrs. no trouble) with 6 ea. of the undrilled on Intake valves. I have reviewed the Association's June 2014 postings and TB on this situation and found no definitive proper blend of rockers.

I have the undrilled units enroute, just another expense on a very expensive overhaul. We are using plus +30 pushrods on 6 cylinders, I wonder if the rocker ratio is the same on both styles?

I have a spare short block, and am waiting for an STC for higher compression pistons for a more HP (175) Certified Engine (2024) maybe.

Respectfully, JD Smith 9976A 1950 170A

[Bruce Fenstermacher]

JD,

Drilled rockers must be used on the exhaust. I swear they could be used on the intake as well but can not for the moment find supporting documentation. So I called Continental tech support.

Talked to Neil in tech support. He was familiar with the drilled and undrilled rockers. He said they are the same other than the hole. So you could physically put them on either side. He then stated that if it is done you could expect low oil pressure from the excessive (twice as many) squirt holes.

He said he knows it's been done. He asked why I'd want to squirt cooling oil on a valve that does not want to be cooled. I said I don't but that I have 12 drilled rockers that have been installed and operation flawlessly for the last 40 years and at $500 a pop I don't want to replace them unnecessarily. He said he understood.

He said I wouldn't be the first to use drilled rockers on the intake but Continental has no instructions to sanction it.

Ouch. This could hurt.

[n2582d]

Sure would be tempting to press in a brass (copper?) rivet into the oil orifice, or replace the rivet above the squirt hole with a longer one. 10 cents vs. $500. Tempting, but no doubt illegal without some basis of approval.

[9976AJds]

Thanks men, you have clarified to issue. My IA says that in the 1980's many shops just replaced the undrilled units thinking the extra oil would work better. Also the drilled units were cheap and an available replacement (New-Teck). Anyway, I am now scrounging up 6 of the old type units, but cannot afford a $500.00 price tag.

The Engine shop owner is the last of a breed of knowledgeable craftsmen, he also thought of "pinning" the extra oil hole, but he had no authorization document.

It will all work out somehow, and I'll use the drilled rockers for my "Super 0300" in the future. I have learned several valuable lesions with my 1950 C170A, never buy any plane who looks great but spent 40 years hangar bound due to not flying. Mine had only 200 hours in the past 30 years and 10 in the past fifteen. The long distance pre-buy never caught the years of cylinder rust that ground off my piston pins as I flew home from California, and around SE until the dreaded 2016 Annual. The engine had several accessory AD's overdue (Mags, and Carburetor) but ran great. The overhaul was necessary for safety of flight, and I am hopeful to fly into my eighty's with 9976A. Respectfully, JD Smith

[lowNslow]

I know they have higher compression cylinders for the O-200/O-300 but I did not know there was an STC in the works to use them on a certified engine. Who is doing this??

[9976AJds]

Karl, the STC research and certification is being done buy an unknown company, but the Engine Shop in California area is where I hope to get my Certified top overhaul kit. Most likely require all new Cylinder Assemblies, and other hopeful minor engine mods (re-jet Carb, etc.). We estimate the cost around 10K+ with new cylinders, we'll see.

It could be years away, in the meantime I am just trying to get 145HP going again. Thanks JD

[GAHorn]

Using drilled rockers on intakes is unlikely to make any noticeable difference in oil pressure because the oil which reaches the rocker is provided by the natural pumping action of the lifter-body pushing oil up the hollow pushrod. The oil which travels up the pushrod is dumped into the rocker-box on both valves.... with a drilled rocker merely providing another place to exit (splashed onto the valve-stem.) In other words, the lifter, operated by the cam, rotating at half crankshaft speed, will pump the same amount of oil with each stroke regardless of the number of holes for that oil to exit.

While no basis for installing drilled rockers on intakes exists from Continental....there are a lot of engines out there in that condition which suffer no problems as the result. Equally, there's no evidence they benefit from it either. The TCM Ovhl Manual instructs to install non drilled rockers on intakes and drilled rockers on exhausts. SB M77-19 only confirms to install drilled rockers on exhausts. No approval basis is mentioned for drilled rockers on intakes.

If memory serves, an O300 pumps two gallons of oil thru the system every minute at cruise RPM. (In other words, every minute your O300 pushes it's entire sump quantity of 8 qts thru the engine.) Lycomings much less than that, (again if memory serves, less than 1 gal/min) and is often quoted as why Lycs suffer more valve problems and need sodium-filled valves.

For a detailed read on the differences between Lyc and Cont and their valve lifters and oil distribution (and to simply feel good about your Continental engine lifter design compared to the other brand) read: http://occonline.occ.cccd.edu/online/rf ... appets.PDF

[hilltop170]

Yeah, like when Continental did not Locktite the 3/8" pipe plug in the front of my brand new IO-360 crankshaft and it worked loose after less than 10 hours and started blowing oil on the windshield and only had 1-1/2 threads left before it fell out completely and Continental just shrugged it off, yeah, like that.

[rupertjl]

If memory serves, an O300 pumps two gallons of oil thru the system every minute at cruise RPM. (In other words, every minute your O300 pushes it's entire sump quantity of 8 qts thru the engine.) Lycomings much less than that, (again if memory serves, less than 1 gal/min) and is often quoted as why Lycs suffer more valve problems and need sodium-filled valves.

George,

Just wanted to clarify-Lycoming oil pumps are in the 7-9 gallon per minute range depending on size of the impellers in the oil pump.

-Jud

[GAHorn]

Jud, my comment was in regards to oil pumped thru the valve train, not the capability of oil pump output. Lycoming spills a large amount of pump output back to the sump via the left-side galleries (which also helps explain why most Lyc valve failures occur on the right side of the engine.)
Bill Marvel and Bill Scott are writers/engine-overhaulers who did extensive studies on Lycoming valve failures due to tappet and oil system design differences of the engines. I'll attempt to locate that research article (it's in several hard-drives past somewhere), but the difference between Continental and Lycoming was stark and shocking.
Although not the article I'm remembering, here is one of their studies (six page article, click on the link at the bottom of page to read subsequent pages):
http://precisionengine.home.mindspring.com/engine1.htm

[9976AJds]

Gentlemen thanks for the advice and lubrication education. We test ran the engine on a test cell last week, installing this week and next. I am proud of the detailed and extensive overhaul for sure, and will send a photo when I get completed.

We have the required blend of rockers now, thanks to Mr. Kennet Dejesus of Ohio, and John Jewell Engines, Holley Springs, MS. Mike Schlender of Wisconsin provided an almost new muffler and header pipes. With no-blow exhaust gaskets we are now set for years of hopeful - non-major repair flying. We are also hopeful the Real Gasket push rod tubes provide a no oil loss flight regime, and clean undercarriage.

The cost was very high due to most internal parts worn/rusted beyond safe limits. I now have "The most expensive 1950 C-170A in the world". I computed my monetary recovery to be about 25 years thus allowing my nephew; also a pilot to sell at break even in 2042, well after I am long gone. Regards, JD Smith