pro design cool head failure

[stroberts22]

I noticed I was losing coolant and the water jacket was getting pressure from the combustion chamber so I thought I had a bad head gasket but when I tore it down the head had a huge crack in the dome. Is this common for these heads? It's a 22cc so compression wasn't to crazy. I put a stock head back on for the time being but if this is a problem with these heads I might just keep the stock one on the machine.

[C-Leigh Racing]

I would have to say, in all my years of dealing with 2 strokes & 250R engines, a cracked dome in a Pro Design head, that would be a first one I've ever heard of.

Now if you were asking about a high compression 250R build, with a tight fitted to the bore cast piston & it cracked right across the top from one side to the other, now I would say I've seen that before & believe it or not the engine was running good, won the main the Saturday night before it was found.
Cracked Pro Design dome, you have the first man I know of.

I wouldnt be surprised, if you was to send it to Pro Design, they probably would replace it free if you had a nice sounding letter along with it.
Just like an Apple for the teacher, guess whos the teacher pet afterwards.
Neil

[stroberts22]

Here's a picture of the crack. I try to contact them but with my luck I'll just buy another dome myself.

[Jerry Hall]

Here's a picture of the crack. I try to contact them but with my luck I'll just buy another dome myself.

This is not uncommon on the low compression domes.  The dimensions of the "wet" side of the dome is the same as the high compression domes making the dome thickness to thin in key areas.  The fins are not necessary for cooling.  The fins trap steam bubbles, add unnecessary weight and cause a stress risers to occur  between the fins when the engine fires.


We see a similar problem on the piston crown of many of the aftermarket low-compression forged four-stroke pistons.  The piston companies usually use the same forging blank and machine the top of the piston to lower the compression.  Guys buy the low compression pistons to make their engine more reliable but the pistons are not as strong as the high compression pistons due to the thin piston crown.

[C-Leigh Racing]

Good point there Mr Hall.
With that being as it is, sounds like another good reason to stay away from low compression & pump gas to keep the thickness of the dome thicker.

Man, you cant win with those 4 pokers, either pay me now or pay me later, but in some cases, it pay now & pay later as well.
Neil

[rsss396]

I did that on a pro design cr500 dome and I know of another guy a prodesign coolhead that did the same.
I would be best if pro design would just quit making the head insert with the fins since it is of no advantage.

[stroberts22]

I'm going to reuse this head and was wondering what cc of insert in need for around 190 psi with 69.5 piston? Plus with this big of piston does the head need to be modified any?

[traxman]

I have had 2 or 3 Coolhead domes fail in the same place but these were 295 domes set up @ 17:1 and 15:1 ratio's and they failed very quick.. I agree with rsss that fin design needs to go, everyone broke in the same spot the trade off for what little extra cooling there might be is not worth the additional strength. For you info, that motor made it 4 years with a stock head with a recut dome set-up @ 15:1 before a failure.

[Jerry Hall]

I have had 2 or 3 Coolhead domes fail in the same place but these were 295 domes set up @ 17:1 and 15:1 ratio's and they failed very quick.. I agree with rsss that fin design needs to go, everyone broke in the same spot the trade off for what little extra cooling there might be is not worth the additional strength. For you info, that motor made it 4 years with a stock head with a recut dome set-up @ 15:1 before a failure.

The horizontal fins on domes do not help when liquid cooled.  The fins trap steam bubbles and keep the water from making full contact with the hot surfaces.  This is just another example of what happens when layman's logic/common sense is used to design parts that should have be done by those that have training and understanding in convective heat transfer when liquid is used as the cooling medium.  

Design errors are becoming more common in the aftermarket performance parts industry as aerospace machine shops are losing machining contracts with cuts in the defense budget. Aerospace machine shops have made a living biding on making high tech parts from blueprints of parts that have already been designed and tested.  The majority of the design errors like the fins on the dome inserts occur when the machine shops step outside their field of expertise which is machine work and start designing and making their own parts.  Poorly designed parts are created when designed by those that obviously did not have the necessary experience or training in the areas of science required.

[poli250]

first you talk flow bench and dyno as tools. now you rip on poor design cool heads. you sound like carlos bud. sure you are not carlos imaginary friend- jerry? just ribbing you man. sitting here bored wifes shopping. lol

[Jerry Hall]

first you talk flow bench and dyno as tools. now you rip on poor design cool heads. you sound like carlos bud. sure you are not carlos imaginary friend- jerry? just ribbing you man. sitting here bored wifes shopping. lol

I am on the phone most of my work day taking calls from guys that have spent their hard earned money on parts that do not perform as advertised.  For some reason, guys in the off road industry are real suckers for anything that has the words CNC,  Billet,  6061 T6,  Titanium,  CAD/CAM designed, 304 stainless, 316 stainless, carbon fiber etc. in the advertisement for the part.  

I do not like to see someone spend the same amount of money two or three times to finally get the results they were expecting had they done their home work.  Reading all of the stuff on all of the forums and watching Utube videos is only a small portion of "doing your research" or "doing your homework".

Because someone has a website or a big add in a magazine, does not guarantee the business is reputable or has the experience needed to help you with your project.  There are a lot of "impostors" on many of the forums that are not real people but persons employed to pump certain companies products and services.  Before you spend your money, talk to a lot guys in person or on the phone about their personal experiences, satisfaction or dissatisfaction with products and services from parts manufactures and engine builders.


Sorry or the rant, just venting a little.   .............I listen to too many grown men cry on a daily basis.  I am a engine builder and not a grief counselor for guys experiencing buyers remorse.

[traxman]

I am on the phone most of my work day taking calls from guys that have spent their hard earned money on parts that do not perform as advertised.  For some reason, guys in the off road industry are real suckers for anything that has the words CNC,  Billet,  6061T6,  Titanium,  CAD/CAM designed, 304 stainless, 316 stainless, carbon fiber etc. in the advertisement for the part.  

Oh &$^*!!! You just described my drag bike... :frown-new:

[poli250]

so pro deign who makes cool heads is a cnc aircraft shop makes billet parts, advertises, web site, mags, has been around for ever, makes a poor design head? not crying, trying to learn.

[udontknowme]

if the dome cracks that would suggest a crap design.  or so it seems

[poli250]

if the dome cracks that would suggest a crap design.  or so it seems

hear you. i wont be buying a cool head.