Skip to main content
000000 000003 000006 000009 000012 000015 000018 000021 000024 000027 000030 000033 000036 000039 000042 000045 000048 000051 000054 000057 000060 000063 000066 000069 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
English French German Italian Spanish

Refitting a Commando cylinder head

Forums

Head gasket blowing so going to take the head off make sure surface is flat and refit with a copper  gasket (annealed) any tips please?

Permalink

Chris

Lots of people should be able to help with their views, but you need to give a little bit of history, if you have any: i.e. have you had the head off, how many miles?

If it is blowing it is either: head face distorted, damaged, badly fitted and not re-torqued, or stainless studs might be implicated.

Most advice says to use a composite gasket and check the head is flat by testing it on a blued glass plate.

Norm

Permalink

Check that the area around the studs in the head are relieved where the threads start and aren't raised above the surface. This can prevent the head sitting fully down.

Don't forget to check that the barrels are flat too!

 Remember that a  surface finish that is too smooth is worse than one that is too rough.

My tip? If you are checking flatness with 'wet and dry' on plate glass, don't go finer than 120 grit.

Regards,  George. 

Permalink

Before taking everything apart, why not try replacing just the four large head bolts [the ones either side of the spark plugs] and tightening them to 30ftlbs?  Original, high-tensile bolts will seal much better than stainless items.  You should buy new bolts anyway so why not start there and see if your gasket is still blowing.  Another tip would be to buy and fit a PCV in the return feed to the oil tank; this can make a considerable difference to the ability of the head to breathe.  It is, after all, pressure that is forcing the oil out of any small clearances.  

Either way, Good Luck! 

Thanks, not sure of the history but I’m going to take the head and barrels off ....I’m fitting a decompression plate under the barrels .....will flatten head on plate glass then use a composite gasket?

Currently all the bolts and nuts are Stainless....should I replace with standard HT ones?

ATB Chris

Permalink

= 'positive crankcase ventilation' - uses a one-way valve that lets air/gas out of the crankcase and stops air getting in thus creating a mild vacuum and helping to prevent oil leaks. They do help ... .

Permalink

Chris

Stainless studs and bolts to secure the head and barrel are not a good idea and should be replaced with genuine HT steel items. Using them to hold on mudguards is fine. It is very probable that they have stretched in use and caused the gasket to fail. Stainless nuts on the engine shouldn't be a problem IF they are strong enough.

Permalink

Colin has raised a point which catches a good number of people out. ie.......they fit a cylinder head that has been skimmed and then refit it with a dubious head gasket and dodgy headbolts. Often the latter being cheap Stainless items. 

The skimming of the cylinder head makes it thinner and massively increases the chances of the dodgy length headbolts bottoming out. Throw in the mix an iffy head gasket and you are going to get possible problems with a head leaking oil plus valve adjusters that run out of thread. 

Fitting a compression plate can also cause issues with pushrod lengths and may lead to adjusters trying poke holes in the roof of the head.Lower compression pistons are a safer route here.

 

Norton Owners Club Website by White-Hot Design

Privacy Policy