84mm 61x uses which head?

bored&stroked

bored&stroked

Urban redneck
Location
AZ
Do I run a 701 head or 760 head? Can a 701 head be re-chambered to work with 84mm? Going to shave it either way to run 180ish psi
 
X

X2Kid

Location
Canberra, Australia.
I think use of a 701 head is good up to about 83mm bore and then you have to go big ('U' prefix head, from memory). I'll let the experts expand on my post as this is all off the top of my head.
 
john zigler

john zigler

Vendor Account
Location
wisconsin
You can run a stock head, but you really should have the domes / squish cut to the proper bore. Failure to do so leaves a "Shelf" at the top of the bore, and possible detonation.

Same with the head gasket. 701 and 760 are totally different gaskets, both in thickness, and water flow.

We have a special OE type 701 gasket for big bore good for up to 85mm;

https://www.watcon.com/engine/gaskets/head-gasket

I can also cut your head for you, if you do not know anyone local, and want to send it to me.
 
JetManiac

JetManiac

Stoked
Site Supporter
Vendor Account
Location
orlando
bored&stroked said:
Yes stock heads. I'm not shelling out $300+ just to be shiney.
Click to expand...

While decking a stock head will increase compression, the stock head gasket still is very thick so squish is large, and performance is still not as good.
A 'shiney' head has a much tighter squish band and better dome design which together makes more power that a stock decked head.

That said, you can run a thinner 760 head gasket with your stock 701 head and it will work fine at 84mm bore. Stock 760 heads have unequal sized domes so stick with the 701 head.
 
Pro-pulsion

Pro-pulsion

Location
Ontario, Canada
I just did this very thing this past Spring. Put a 760 stock head and stock 760 head gasket on a 701 61x 84mil bored. The Blaster ran exceptionally well but as the Maniac man stated, the domes are different cc sizes. The Mag side dome was showing 150 compression, the PTO side showed 135. At first, not knowing this I panicked and went straight to the service manual to find that these numbers are proper. They make the rear dome larger to help with cooling that side of the engine since the PTO typically runs hotter. This ski runs really well though so no need to worry if you do go the full stock route like that.
 
bored&stroked

bored&stroked

Urban redneck
Location
AZ
JetManiac said:
While decking a stock head will increase compression, the stock head gasket still is very thick so squish is large, and performance is still not as good.
A 'shiney' head has a much tighter squish band and better dome design which together makes more power that a stock decked head.
Click to expand...
When cutting new domes into a head, can't the head gasket thickness be taken into account and the domes adjusted accordingly?
 
john zigler

john zigler

Vendor Account
Location
wisconsin
Just an FYI for all reading this thread. If you run a stock 760 head, you are not able to run the stock 701 exhaust pipe, as the pipe mount bosses are different.

We have set many up this way. 701 cly at 84mm, stock head with domes cut out to 85mm and re-shaped for 175 lbs pump gas. Able to run a stock pipe, works well, and sleeperish.
 
Freakrider

Freakrider

X247
Location
Tampa Bay area
Riva machine shop years ago would deck the 701 head for 185 PSI and then reshaped domes to adjust the squish accordingly for safe high compression. I still have one that I ran successfully on a blaster, it ripped nice. Definitely would run a girdled head on a ported cylinder that's worth money to prevent potential cracks on intake side.
 
bored&stroked

bored&stroked

Urban redneck
Location
AZ
I already have a 701 head that was modded by group K including cutting off the oem exhaust mount bosses and giving 175psi. Also have a protec girdle that I had cut into a half girdle to work with the head. I didn't know if I could re-cut it to work with the 84mm or if a 760 head was required. I'm stretching my jetski budget this year to put the new top end on, spending the big bucks for an aftermarket head just isn't an option at this point.
 
#ZERO

#ZERO

Beach Bum
Location
Florida - U.S.A.
I would recommend using an OEM Yamaha 760 64X head gasket part number: 64X-11181-00-00 that uses a three-piece stainless steel riveted design that is rubber coated with a .025-inch thickness.

The 701 61X heads have a single cooling hose exit and the 760 64X heads use a dual cooling hose exit; either head will work once its milled down to the desired compression wanted along modifying the squish band angle & depth to the appropriate engine spec.
 

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dillmu967

dillmu967

Location
Meadow Lake, Saskatchewan
Can I run a 61x or 62t head on a 760 or do I need to run a 64u head? I have the 64x 760 head with the different compression per cylinder is this a huge loss in power? Building a stock class ski so want to get the most I can out of it.
 
J

jpswift1

Location
Buffalo, NY
#ZERO said:
I would recommend using an OEM Yamaha 760 64X head gasket part number: 64X-11181-00-00 that uses a three-piece stainless steel riveted design that is rubber coated with a .025-inch thickness.

The 701 61X heads have a single cooling hose exit and the 760 64X heads use a dual cooling hose exit; either head will work once its milled down to the desired compression wanted along modifying the squish band angle & depth to the appropriate engine spec.
Click to expand...

I know this is an old thread, but I just added a second cooling elbow on my stock milled 61X head and figured I'd get your input. It sounds like the 760 head gasket, since it is not as thick as the 701 head gasket, would give slightly more compression and it would have the correct holes in it so the water would flow better for my 61x head with the newly added dual cooling, correct?
 
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