Skip to main content
000000 000001 000002 000003 000004 000005 000006 000007 000008 000009 000010 000011 000012 000013 000014 000015 000016 000017 000018 000019 000020 000021 000022 000023 000024 000025 000026 000027 000028 000029 000030 000031 000032 000033 000034 000035 000036 000037 000038 000039 000040 000041 000042 000043 000044 000045 000046 000047 000048 000049 000050 000051 000052 000053 000054 000055 000056 000057 000058 000059 000060 000061 000062 000063 000064 000065 000066 000067 000068 000069 000070 000071 000072 000075 000078 000081 000084 000087 000090 000093 000096 000099 000102 000105 000108 000111 000114 000117 000120 000123 000126 000129 000132 000135 000138 000141 000144 000147 000150 000153 000156 000159 000162 000165 000168 000171 000174 000177 000180 000183 000186 000189 000192 000195 000198 000201 000204 000207 000210 000213 000216 000219 000222 000225 000228 000231 000234 000237 000240 000243 000246 000249 000252 000255 000258 000261 000264 000267 000270 000273 000276 000279 000282 000285 000288 000291 000294 000297 000300 000303 000306 000309 000312 000318 000321 000324 000327 000330 000333 000336 000339 000342 000345 000348 000351 000354 000357 000360 000363 000366 000369 000372 000375 000378 000381 000384 000387 000390 000393 000396 000399 000402 000405 000408 000411 000414 000417 000420 000423 000426 000429 000432 000435 000438 000441 000444 000447 000450 000453 000456 000459 000462 000465 000468 000471 000474 000477 000480 000483 000486 000489 000492 000495 000498 000501 000504 000507 000510 000513 000516 000519 000522 000525 000528 000531 000534 000537 000540 000543 000546 000549 000552 000555 000558 000561 000564 000567 000570 000573 000576 000579 000582 000585 000588 000591 000594 000597 000600 000603 000606 000609 000612 000615 000618 000621 000624 000627 000630 000633 000636 000639 000642 000645 000648 000651 000654 000657 000660 000663 000666 000669 000672 000675 000678 000681 000684 000687 000690 000693 000696 000699 000702 000705 000708 000711 000714 000717 000720 000723 000726 000729 000732 000735 000738 000741 000744 000747 000750 000753 000756 000759 000762 000765 000768 000771 000774 000777 000780 000783 000786 000789 000792 000795 000798 000801 000804 000807 000810 000813 000816 000819 000822 000825 000828 000831 000834 000837 000840 000843 000846 000849 000852 000855 000858 000861 000864 000867 000870 000873 000876 000879 000882 000883 1.slide1 2.slide2 3.slide3 4.slide4 5.slide5
English French German Italian Spanish

Cylinder heads and exhaust ports

Forums

Hi. I have three Dommie 99 cylinder heads. They are all marked 22707. One of them is 22707H, one is 22707Y and the third has no letter after the number, it’s just plain old ‘22707’ (there’s no sign of a letter having been removed). All three heads have the same carb manifold fixings -  vertically spaced screws in two pairs.

I decided to use the ‘plain’ 22707 head as it’s in the best condition.  The underside of the head is stamped ‘S.S’ - does that mean it’s a 99SS head? If so, what’s the difference between that and a standard 99 head - it looks identical to the other heads. Or perhaps it’s from an early pre-downdraft 650SS, if such a thing existed?

The ports for the exhaust pipe fixing rings have the same thread pitch but different pitch angles (60 vs 55?) - the ‘Y’ and ‘H’ heads have a more steeply angled thread form than the ‘plain’ head. It’s odd that Norton would change such a basic thing for what seems like no good reason.

The threaded exhaust ports themselves are also a different bore diameter on  the ‘Y’ head which means that the exhaust pipes for that head can’t be used on the ‘plain’ head or the ‘H’ head as the flange that fits into the bore is wider. The difference is only 0.7mm but it’s enough to stop the pipes going in on the ‘plain’ and ‘H’ heads.

It seems odd that Norton would go to such a large amount of trouble to cast  different cylinder heads with only slightly different sizes in some areas for no apparent purpose or gain.

Can anyone shed some information as to what my ‘SS’ head is and why all the heads are different?

I imagine I’ll need to get some ‘one size fits all’ exhaust pipes and carefully grind a bit off the flange diameter where it fits into the head.

Thanks

Regards

Tony

Permalink

22707 is actually the skull casting mold for the picket fence side heads. The suffix does not change the basic head or even when they eventually stopped using the # on the molds.

It is used on both 88SS/136 heads and S650/136 heads.

See them here:   http://atlanticgreen.com/nhth.htm

The factory exhaust port threads never changed. So one of your heads is a bodge to accomodate big flange pipes. Someone may have chased the port threads with a 60 degree UNS tap as they are much easier to find and possibly much cheaper. My UNS tap was only $160. The exhaust nuts may be aftermarket.

SS heads mainly had different springs to be compatible with the "SS cam.

Permalink

Thanks David. That link to the Atlantic Green head info was very helpful. It looks like I can use my  ‘plain’ 22707 head without any worries. I was worried that the ‘SS’ stamping might cause problems but if the only difference is  stronger springs to cope with the SS cam, I can just use the standard springs with my QR cam. I’ve got the exhaust roses fitting nicely now so I just need to get some pipes. Thanks again for your help.

Regards

Tony

 

Norton Owners Club Website by White-Hot Design

Privacy Policy