[GusRV8]

I am becoming a part owner in an RV-4 carrying a normally aspirated O-360-A1A and spinning a Hartzel prop. The combination was dynamically balanced on 7/16/2008. Recently the #4 cylinder was replaced and has reached the break in period. It was running hotter than the #2 cylinder by about 15 degrees, but now that it's broken in both are more or less equal, yet still consistently about 40 degrees hotter than cyls 1/3.

A&P is suggesting a cowl flap but before we go ahead and start cutting I wanted to check here and see if anyone has had a similar problem and what their solution was short of installing a flap.

I haven't personally checked the baffeling yet but the A&P says it's probably not the cause.

Any suggestions as to what to try or where to look would be greatly appreciated!

Am building a -8 but am not this far along yet. Hoping to at least be able to fly some during the build process (yeah, I know it'll take away from the build itself but I can only be earthbound for so long!).

Thanks in advance!
Gus

 

[sailvi767]

What are the actual temps? If your under 380 on the hot cylinders during a normal climb I might just live with it. Does the 40 degree split continue at cruise?

George

 

[GusRV8]

Temps

The guys who are flying it are having to fly rich to keep it below 380-390 on those two cylinders. The other two are at 350-360 in cruise. The hot side isn't allowing much, if any leaning, let alone LOP or ROP operations right now. And yes, the split is there while in cruise as far as I know. We were pondering if whether an ascending/descending blade would have anything to do with one side being hotter than the other? But I've never seen any discussion along those lines in this forum or any other, not that it doesn't exist. Like I said, I haven't checked the inlets or baffeling myself yet, the airplane is buttoned up and on a crosscountry right now so can't take a look at it until after the weekend when it returns.

 

[Doug]

Just wondering .... Do you have a heater muff on the exhaust beneath the 2/4 cylinders?

A long shot but if you do it may be restricting the air exiting from the cowling on this side of the engine.

 

[GusRV8]

Thanks Doug

It does have heat, will have to ask or look at it to see where the muff is. If there is one there, and it is restricting, possible options to correct? Thanks for the idea, will let you know what I find.

UPDATE: 1/3 go to the heat muff, 2/4 go to the oil cooler. Description is that all of the 'top' cylinder air is routed to each respectively. We probably need to check the baffles to ensure adequate air to 1) the bottom portions of cylinders 2/4 or 2) block some of the air going to the oil cooler to allow better flow across the top halves of 2/4 where the baffle currently is to reduce what might be a more than normal restriction on that side. Will have to take a picture or look at the baffles to see exactly what is going on. Was told that the baffle 'cuts' across the half of the cylinder, will have to see where they hit so we're getting maximum flow across the fins from top to bottom. Will look at also measuring inlet vs outlet sizes and ensure we have adequate allowance on the outlet side. Also there was a suggestion to use a 'washer' type spacer to create some distance between the baffle and the fins to again allow better/more airflow; that was tried without measurable difference, but will ensure the created gaps are properly sealed.

Concerned about reducing/changing oil cooler airflow as right now oil temps are not a problem except on hot desert days at slow airspeed so any correction will hopefully not affect that portion of the system...but everything is usually a tradeoff.