advice on cht

having problems with cylinder temp on rv-6a #4 copilot rear was running hot
and we closed off sides of air dams in inlets on top cowling and now #2 pilot front cylinder is running hot ive read search on this site and im looking for idears we have stock cowling and baffles and louvers in bottom of cowling about 3x6 on each side stock opening thanks in advance
bob

First, let's make sure I'm on the same pages as you with regard to cylinder number. Sitting in the pilots seat, the right front cylinder is #1, the left front is #2, the right rear is #3, and the left rear is #4.

Typically, #3 is the hottest cylinder and #1 is the coolest. This imbalance is usually fixed by applying a short air dam that runs an inch or inch and a half up the front of #1. That's what I did and it balanced things for me.

Is your engine fuel injected, or is there anything else we need to know? How many hours are on the engine? What are the oil temperatures? What are typical cruise and climb CHT readings for each of your cylinders?

CHT

were on the same page
#1 is the coolest in cruise at 290
#2 at 420
#3 at 340
#4 at 390
on take off clime out at 150mph #2 up to 450 so i pull back to 2200
fixed picht sen rv metal 85 picht carb 0-360 aerosport
after climbing and level off and cruise speed bring ing power up to 2500 temps aboverunning rich of lean

Do you have any "air dams" in front of #2? If so remove them and try again. Also it is possible, and quite helpful, to put a spacer between the baffle and the cylinder at the very forward outboard end of the cylinder. Two washers under the bolt at that location should help. This is ususally done on the #3 at the same time but based on your temperatures I would hold off.

carb?

What Carb are you using?
10-3878 or the richer 10-4164
aerosport normally ships the richer carb or modifies the leaner one.
There should be an 'M' stamped after the model # like 10-3878-M
if it has been modified.

Tom Martin said:

Also it is possible, and quite helpful, to put a spacer between the baffle and the cylinder at the very forward outboard end of the cylinder. Two washers under the bolt at that location should help. This is ususally done on the #3 at the same time but based on your temperatures I would hold off.

Click to expand...

ok I have heard this described a dozen times but I still dont get where these washers go.

So Im sitting in my plane. Washers on cyl 4 would go?
1. Aft side of cylinder, near engine iso mount bolt, between baffle and cylinder?
2. Baffle on left side of the cyl surrounding the valve cover?

The washer or spacer needs to go aft of #3 (right rear). Same issue front side of #2 (front left). The fins have zero depth right where the baffles normally touch them, so the fins below the baffle at that location do not get cooling air. This zero depth situation does not go all the way across (left - right) the cylinders, so one needs to examine the fins to understand this. Shimming the baffles a fair bit, maybe 1/8", but finding a way to seal the gap where the fins do have depth would seem to be ideal.

Hard to imagine why the cylinders are designed this way.