Anyone tigged a VW aircooled head?

[cardiffrob]

I have an aeroengine that has a habit of overheating and am after finding out what might work to weld on extra strips of alloy to the cooling fins.
Any thoughts?

 

[hotrodder]

Welded lots of aircooled VW heads. In the crawling/walking/running analogy of the cowling thread welding cylinder heads (or castings in general) would be sprinting...

Would welding not effect the engines certification i.e. not allowed full stop or needs to be performed to certain procedures by a suitably qualified welder? Not up to speed on what's 'free' or restricted with regards to LAA but have a customer that flies similar things that's asked me about exhausts and the like before- he reckoned exhausts could be welded by anyone as long as they passed inspection whereas an engine mount (fairly obviously) would require a welder with suitable 'codings' (relevant material group and positions of CAA BCAR A8-10 or AWS D17.1?)

Are we talking 'factory' cylinder head castings (044's etc) or aftermarket (scat or the like) which are generally much more basic/crude in the exhaust port fin area? Are they just running a bit hot or are bits being cooked?

 

[brightspark]

I have an aeroengine that has a habit of overheating and am after finding out what might work to weld on extra strips of alloy to the cooling fins.
Any thoughts?

what does everyone else do .is it a common fault ?if so how have they ovecome it

 

[cardiffrob]

The aeroplane in question has no 'firewall forwards' in the plans so anything goes, so long as it meets 'suitable standards' of manufacture. Being a VW, you can fit a factory head or one that has been rebuilt and there is no requirement for traceability.
Generally people buy new ones from the US but none come with bigger cooling fins. They only ever crack round the exhaust ports due to low speed climbing reducing the cooling airflow.
I'd ideally want to tack some 1 inch squares onto the fins round the exhaust ports on standard factory 1970s era small valve, twin port heads.

So far I have kept it alive with huge cowling intakes (very unaerodynamic!)

 

[CKJDJK]

Why is it overheating? Is the mixture to weak or the timing incorrect? Is the air flow restiricted? Looking at the photo your cowling has volume but could you change the shape so that the cooling air is forced over the fins and not just held around the head? More air flow equals mor cooling.
Chris

 

[cardiffrob]

Those heads are baffled, flowed and have all of the flashing removed from the fins. It is all about the lack of airflow at low speed compared to the car engine at similar revs (2900 rpm, 65hp, 40mph) when the aero engine is constantly pulling hard against the drag. You can't get more revs without the prop tips going supersonic so it is always going to be like trying to go uphill in 5th gear with a small engine....hard work.
The mixture is spot on (wideband lambda sensor) and the timing is correct, using modified Ford Mondeo ignition coils (2 sparkplugs per cylinder) and a series of hall-effect transducers to run the timing.
It simply produces too much heat at low speed for the aircooled heads to disperse. The 'plenum chamber' area above the heads is cowled such that all of the air captured by the cowling is forced through the gills of the heads and barrels before being dumped overboard at the bottom of the heads.

 

[intergrale4x4]

Air Flow

Looks like you have plenty air going in the front but can the hot air flow out the rear ?? Just a thought !! "Loads a huge engine kit car fits" in the past

Craig

 

[Uniqueusername]

Two things spring to mind immediately......

Airflow; before thinking about getting air in you should always think about getting it out.
I've even had overheating problems on flatfront escorts simply because air couldn't escape, ideally it should be pulled out and not pushed through, even in the aero world.

Mixture; Spot on what ? Stoic was way to hot for autograss engines (sprint race) and we had to run excessively rich or they'd sieze before having chance to dump heat into the water. we got rid of the thermostat and replaced it with a pressure plate for similar reasons.

Thirdly; I've been inside three of these engines lately and all had cracked heads.....

 

[intergrale4x4]

Two things spring to mind immediately......

Airflow; before thinking about getting air in you should always think about getting it out.
I've even had overheating problems on flatfront escorts simply because air couldn't escape, ideally it should be pulled out and not pushed through, even in the aero world.

Could a swore I just said that
Cs

 

[brightspark]

Could a swore I just said that
Cs

its an echo in the room

 

[Uniqueusername]

Could a swore I just said that
Cs

You did, and look at the time it was written.
Using two fingers to type i probably started before you and still finished 5 minutes later.
I'm a better welder than typist.......

 

[intergrale4x4]

no Offence ment !! I'm new here but been building cars and bikes way longer than I'd like to admit and looking for a new Mig "Which brought me here" Portamig looks like the very fellow I'm after. Get the wind going past it for Cooling I recon as well mate !!
Cs

 

[hotrodder]

Rob said

The 'plenum chamber' area above the heads is cowled such that all of the air captured by the cowling is forced through the gills of the heads and barrels before being dumped overboard at the bottom of the heads.

one hour before the echoing about airflow and ducting started

What are the cylinder head temps in a low speed climb? During cruise? Does cracking only effect the rear most cylinders or any/all of 'em? Obviously ducting and airflow are going to differ a lot from the factory set up in a back of beetle but i was expecting to see something fairly similar around the cylinder heads albeit fed differently.

I'd ideally want to tack some 1 inch squares onto the fins round the exhaust ports on standard factory 1970s era small valve, twin port heads.

I can't see this making much of a difference personally. Exhaust ports are pretty heavily finned on stock heads, albeit in a way designed to work with the factory cooling system. Room to add some fins on the rocker box side of the ports i suppose but depends where the ports crack as to whether it'd have a chance of lowering/stabilising temps

 

[cardiffrob]

The mixture is variable inflight, hence the use of a throttle, mixture lever and lamnda sensor. The CHT gauges and EGT gauges run close to the max permitted but the heads always crack in the same place around the fins where there is insufficient cooling, hence the request for a rod recommendation on this welding forum.
The air outflow is in excess of the 1.5x inflow required and is designed to run at any feasable angle of attack so it isn't a problem.
The aero engine runs at WOT for up to 20 minutes in the climb, producing 65hp approx through heads designed to run 40hp whilst "slow best-climb speed" drops the differential air pressure across the barrels and head, so the heat dissipation properties are marginal at best. This has been discussed at length over the last 40 years by aeroVW peeps and they've always said similar things.
A high drag airframe also requires near WOT in the cruise which is also punishing.

The FAT FIN mod to the VW head is done in the US along with ceramic port coating, both of which work well. Sadly, the cost of the TIG welder precludes much more spending on coating of heads!


So, which rod?

The original FUGLY cowl, baffle and exhaust system cooked the heads enought for the left head to pull out of the block due to overheating/stretchingat about 500 feet after take-off from Spence field a few years ago, hence the attempt to improve the cooling. Zero cooling through the vertical fins of the head!!!

 

[hotrodder]

4043 filler wire, don't make the new fins from a 5xxx series alloy. Castings generally require preheating, min 80C but you may need more with a 160A machine- depends on wall thickness where the extra fins are to be added from amperage POV but complex castings (lots of webs or in this case fins) are more prone to cracking from the localised expansion/contraction forces. Higher preheats will help and lower amperage requirements which will also make welding small bits of Al to a big chunk a tad easier*. Max preheat of 200C.

Don't do too much work in one spot, particularly with higher preheats as the heads will be heat treated and are annealed by heating in the 300 - 400C range (temp and soak time dependant on alloy) i.e. switch between ports on one head to keep the temp gradient sensible and prevent one area getting too hot. Maybe switch between heads too but that's probably only practical with an oven (send the missus away ) or oxy fuel for preheating as it's very boring preheating something like a VW cylinder head with a little MAPP torch or the like

* a relative term, welding small pieces of Al to a big heat hungry chunk is not easy. When the big chunk is a casting and likely to be full of all sorts nasties regardless of how well it's been cleaned it's more difficult.

 

[cardiffrob]

Thanks. I've had a few suggestions from aero sites about the method but not the materials. Mostly they've advised to use fins cut from another head or to make a slightly wavy long fin and to weld it and leave a gap, a bit like a castle ramparts. This would suggest that it might allow some flexing and dissimilar stretching without cracking.
I'm off to Gatwick for a week in the Sim but will have a crack at welding some old bits of fin upon my return.

Cheers!

 

[squazy84]

you need a bigger engine. but you are clearly a brave man so your probably going to stick with the vw,im not clued up on the specific rods to use or the actual welding process,im going to just throw you a few ideas,maybe you can weld an alloy tube onto the hot spot and fill this with water coolant mix and use the natural convectional currents for circulation with the high point of the tube in the airflow stream and a regular radiator ventable pressure cap fitted to the pipe,in older performance petrol engines the valves used to be hollow and filled with salts which at operating temp became liquid and carried the heat up the stem more efficently,run the engine a little richer, i just use shiney rods for cast alloy and dull rods for sheet lol oh and maybe remove the silencer and let the gases out quicker, i thougt you wernt running one

 

[slimjim]

it needs to be Beemer powered

http://spang-air.de/e/html/bmw_-_engine.html





sorry i have failed in answering your question

 

[Uniqueusername]

Exactly where is the low pressure area on those heads ?
You can pressure duct until the cows come home and still not get airflow.
(ask Gartrac)
Adding fins never made any difference on bikes, hence all the water cooled conversions.
But good luck anyway