New Head

[RubenMichelis]

Hello everyone I am starting to modify my engines , I just made a new head for my rossi and after three flights (I practice pylon racing but I did not find any group with as much information as this) the engine towards a different noise I suppose were detonations but I never until now have heard a glow engine detonating and when I removed the head I found these combustion marks. And my question is whether I should adjust squish clearence or compression ratio in case to adjust squish what squish clearence recommended me for 22.000 rpm for a rossi .40 or if I must to adjust compresion ratio what relation I must to use . I use this engine whit original rossi mini pipe .Thanks in advance


Ruben Michelis
Buenos Aires
Argentina

 

[Mario Johnston]

What clearance are were you running?

 

[Al Hobbs]

What is your fuel nitro content?

 

[David Ashcroft]

Looks like a even burn to me ,,although looks like you run plenty of oil..

 

[RubenMichelis]

I am using 0,2mm clearance ,fuel with 5% nitro (we have made a rules for our country with low demand for engines to keep costs limited due to the economic situation we live in) and I have glow plugs rossi turbo from medium to extra cold to test

 

[Terry Keeley]

We don't usually see a burn pattern under the squish band area like that.

0.2mm (0.008") squish is tight enough, is the squish band tapered? What volume is in the head? How much oil? All castor?

 

[ALLAN YUEN]

Look brass button head?

 

[bermudadude]

thought the pylons where in the 40,000 range for that size(?)
if it sounds /runs rough then its def more torque but u dont need any in a plane so raise ex timing. may have too much trapped compression as rpm rises ,that would also limit top rpm.
or slowly decrease comp ratio till it screams .
without any measurements just visual it looks like a big bubble already.
maybe plug is too cold (?) causing really bad ignition timing . if it fires after tdc 2t engines sound really ugly

 

[Al Hobbs]

I also think that your glow plug might be too cold for the fuel's nitro content.

 

[RubenMichelis]

Terry:
when measuring to check the volume of the head I realized that I did not have the head gasketl that because it was aluminum I thought it was placed, by this mistake use the engine without squish clearence since without gasket there is no clearence between the piston and the head , maybe this explains the detonations and piston marks. Head volume is 0.32 cm3 and the squish band is flat not tapered my fuel has 18% oil all castor

Bermudadude and Al:
I was using rossi very cold turbo plugs tending to use the compresion ratio as high as posible I will make tests with warmer plugs

Best regards to all by now

 

[Terry Keeley]

It actually looks better than most of our heads, I usually get some frosting but I run 60% nitro generally on 12% oil (8% synthetic/4% castor).

Might be that the mixture is still burning in the squish area as the cold plug will have a fairly late ignition point. Your 0.32cc head volume if good.

 

[RubenMichelis]

Thanks I will test again follow Your advises . best regards