big fin head mod

I recall a company that made a modification to the XR 600 head that consisted of welding on fin extensions to aid cooling. Does anyone remember who did this mod? Was it effective?

I think that XR's Only still does the big fin heads if you are interested. Before I did that however I would add an oil cooler off of a XR250 or 400 first. I think for the vast majority of riding conditions an oiler cooler would provide the greatest cooling efficiency.

I thought Hunda testing revealed the big fin head worked better than the oil cooler.

well if you think about it, most of the heat generated goes right into the cylinder head where the fins are, from there it is transmitted to the rest of the engine and also the oil. the oil cooler is a good idea but they put fins on the head for a reason, making those fins to a greater surface area will allow more heat to dissipate faster. Cooling just the oil doesnt cool the head much IMO.

heat isnt generated from anywhere else except the combustion chamber and so i would start there if you can.

XRs Only developed the XR race bikes for Honda in the 70s and 80s. They are the ones that started this mod and the only one I know of adding big fins still.

Call up Rob Barnum at Barnumspro.

I weld my own big fin heads.

big-fins5.jpg

big-fins2.jpg

Talk about dredging up an old one. At five and a half years this one has got to be one of the oldest. What do you think the chances are that Deano still owns an aircooled XR?

Captain Midnight,

What type of welding do you use? Would you mind sharing the aluminum alloy, too? Finally, do you have any problems with distortion of the head due to heat?

^^^^What he said - speak on oh wise one!^^^. I'd love to do my own big fin head if its feasible.

Nothing special. Regular aluminum, regular rod. TIG welded. The head has a lot of silcone in the alloy, so get things really clean before welding. I made cardboard templates to get the fins shaped right. Bevel the fins where they join the head, so you can get 100 percent penatration, when welding on the top side only. Give a little extra clearance around the petcock.

Bevel the fins where they join the head, so you can get 100 percent penatration, when welding on the top side only.

For the DIYers out there, that means starting at the bottom(cylinder side) of the head and working upward... :moon:

Damage in $$$ :moon:

Talk about dredging up an old one. At five and a half years this one has got to be one of the oldest. What do you think the chances are that Deano still owns an aircooled XR?

it wud seem the guys from downunder start at the last thread and work their way towards the first :moon:

:cheers:

About 150

I have 2 mates that want to do it on XR400/XR630 but the people in Oz that use to do it, dont anymore...

Thats not bad at all, old thread or not.

Hmm, now do I do the 600R or 650L

Does anyone know if the added fins cool enough to bump up compression slightly without predetination?

I've had it done and it does work well. It does NOT stop the dreaded pinging with a hi-comp piston though.

The pinging comes from lack of quench or squish area.

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