New top end, bad ground-run RPM

[bucaronco]

Guys,

I've invested in four new ECI Titan cylinders for my RV6 (O-320-B3B), due to exhaust port cracks.

The A&P tells me that the initial post-maintenance ground-run was good, except that at full throttle, the engine only reached 2200-2250 RPM, instead of the 2700RPM as called for in the Type Certificate Data sheet.

He was careful to keep oil temps and CHT's below levels specified in the manufacturer's info booklet.

My suspicion is TACH troble of some sort, but my question is this:
Does anyone know of another problem which might cause this after a new top-end job?

THX....Ron

[Mark Burns]

If you have a fixed pitch prop the static RPM is good.

If you have a constant speed prop you might need a new mechanic.

Mark

[LifeofReiley]

Originally Posted by bucaronco

Guys,

I've invested in four new ECI Titan cylinders for my RV6 (O-320-B3B), due to exhaust port cracks.

The A&P tells me that the initial post-maintenance ground-run was good, except that at full throttle, the engine only reached 2200-2250 RPM, instead of the 2700RPM as called for in the Type Certificate Data sheet.

He was careful to keep oil temps and CHT's below levels specified in the manufacturer's info booklet.

My suspicion is TACH troble of some sort, but my question is this:
Does anyone know of another problem which might cause this after a new top-end job?

THX....Ron

Full throttle on the ground static RPM you're in the ball park at 2250. You're not going to make 2700 static. What did you see before on the tach static?

[LifeofReiley]

Originally Posted by Mark Burns

If you have a fixed pitch prop the static RPM is good.

If you have a constant speed prop you might need a new mechanic.

Mark

I would think either way it would appear he may need a new mechanic...

[brenegan]

Were you getting 2700 RPM with your enging/prop combo anytime prior to
just replacing the cylinders?

Something else to check, besides 'get a new mechanic'...
If C/S prop you my check the prop governor. First make sure you have the right one for the prop combo, make sure you are getting full motion stop-to-stop, and make sure it's going high-RPM when it should be and cable is not retreating. It's possible the governor also may need overhaul. Its happened to me but I was only losing about about 75RPM.

The tach can be pinched and not show the right RPM, the cable end can be
worn either on the engine or TACH ends; Another possibility is the cable
is incorrect for the TACH.

If you are not getting what's specified in the TCDS your aircraft is not
airworthy, but you probably already know this.

[Yukon]

Do not do full power static runups with new cylinders. You will cook them. Run it to check for leaks, , cool it down, cowl it up and get airborne. Airflow is insufficient to break in new cylinders on the ground.

[Stephen Lindberg]

Nothing is gained by running on the ground except glazed cylinders. You can check static rpm on your initial takeoff roll. Since the engine is tight it might not make full static rpm with a fixed pitch prop but close is good enough. Run on the ground only enough to make sure nothing is leaking or falling off. Three minutes is enough, including a mag check. Shut down, pull the cowling and look for problems, put it back together, and go have a Coke. Then, taxi promptly to the runway and push the throttle to the stop and leave it there for the next hour while you circle the airport at 3000 feet, then land and pull the cowling again. I ran my 0-290 WOT for the first ten or so hours after OH just like that. About then the oil temp came down and I figured it was mostly broken in, and it was. 500+ hours later it has good, no, great compression and uses about a quart every ten hours or maybe less. To break in an engine you need high pressures on the rings, plenty of airflow over the cylinders, and a rich mixture for additional cooling. In the absence of a test cell this is best accomplished with WOT in flight and at low enough altitude to develop as much power as possible. Minimize ground running as much as possible on a newly overhauled engine. You can find out all you need to know before flight in just a very few minutes. Anymore ground running is counter-productive. (You can tell I am in high dudgeon, it has been a long, irksome day!)

[brenegan]

I disagree. Yes, it's insufficient to break in the cylinders; About an hour or so
of flight and you'll probaby start seeing the CHT rise and then drop to 'normal' levels; but if you are not getting what's specified in the TCDS you shouldn't fly. A full power runup to check RPM is not going to cook the cylinders.

[bucaronco]

Thanks guys, for the replies.

To be honest, I couldn't remember what the static runup value was, since I don't normally do that. Before the new cylinders, I did a mag check and took to the sky (after eng instruments in the green).

My first usual check of RPM has always been after making sure that the centerline is tracking between my legs!... at which time, airspeed was higher, and the RPM that I saw was in the 2500-2700 range. However, the prospect of a "test flight" has me paying closer attention to what's normal and what's not. The A&P did not "squawk" the low RPM, he merely reported the number and left it up to me as to whether or not that was good.

In the mech's defense... he's a young guy, freshly retired from the Airforce, and has grown up on jets. Both he I are on a learning curve with these lil airplanes and recip engines. The difference is that MY learning curve is costing $$$ !

[brenegan]

ECI provides a good booklet on engine break-in instructions. It's on the web now: http://www.eci2fly.com/pages/tech.aspx#breakin