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'74 Mk II, Still Chasing Significant Cyl Head Oil Leak

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'74 Mk II, Still Chasing Significant Cyl Head Oil Leak

Posted by Ron Wellman at June 28. 2017

My '74 Mk II continues to be a problem child with a significant oil leak from the 3rd fin up from the bottom. Have tried soft copper, and OEM fiber gasket, did use additional sealant contrary to many recommendations. Have head resurfaced so it's flat.

Appears that oil is coming from one or more of the 3 front bolt/studs.  I know the gasket should contain this but it hasn't so far.  I do have a new OEM gasket and will reassemble without extra sealant.

Have scrupulously cleaned head and inspected for cracks with uv dye -- found none.

Has anyone ever considered putting very thin cross section oil resistant o-rings just under the bolt and studs to block oil running around the bolt and studs ? Thin enough that they would squeeze into the head and not interfere with properly torquing the head.

Ron Wellman

Midland, MI USA

Re: '74 Mk II, Still Chasing Significant Cyl Head Oil Leak

Posted by john_holmes at June 28. 2017

Best leave your email address off the post, there are spambots trawling forums looking for email addresses to add to spam lists.

On BSA A65's there are head studs they add O rings to, so it works on a similar engine, vitron is the best material for oil and heat resistance. Have you considered removed the studs and reinstalling with a sealant such as Loctite 515 or 518, this will stop oil migrating along the threads.

Also read this thread.

http://www.accessnorton.com/high-temp-head-gasket-sealer-comparison-t27001.html

Re: '74 Mk II, Still Chasing Significant Cyl Head Oil Leak

Posted by Ron Wellman at June 28. 2017

Previously john_holmes wrote:

Best leave your email address off the post, there are spambots trawling forums looking for email addresses to add to spam lists.

On BSA A65's there are head studs they add O rings to, so it works on a similar engine, vitron is the best material for oil and heat resistance. Have you considered removed the studs and reinstalling with a sealant such as Loctite 515 or 518, this will stop oil migrating along the threads.

Also read this thread.

http://www.accessnorton.com/high-temp-head-gasket-sealer-comparison-t27001.html

Re: '74 Mk II, Still Chasing Significant Cyl Head Oil Leak

Posted by Ron Wellman at June 28. 2017

Thank you John for your useful suggestion all around.  Will edit my post and remove my email.  Have thread sealant and will use.  Also will pick up correct sized viton o-rings and put them in place.

I WILL stop the oil leak !

Ron

Re: '74 Mk II, Still Chasing Significant Cyl Head Oil Leak

Posted by christopher_winsby at June 28. 2017

I use standard eyelet gaskets with Wellseal sparingly around holes and fit new washers to bolts.

Re: '74 Mk II, Still Chasing Significant Cyl Head Oil Leak

Posted by alan_blackhurst at June 28. 2017

I had this problem last year. My fault hadn't emptied the breather bottle and the breather pipe was in the emulsified oil. I think that this caused the engine to pressurise. Which showed by leaking badly from the 3rd fin down. I have since fitted a non return valve in the breather pipe from the engine and make sure the breather bottle is emptied regularly. It hasn't leaked since.

Your problem maybe down to poor breathing.

Regards Alan

Re: '74 Mk II, Still Chasing Significant Cyl Head Oil Leak

Posted by richard_payne at June 28. 2017

Third fin up at the front is a favourite spot for oil to appear and the usual causes are either the inlet rocker cover gasket or the rocker spindle cover plates.

It seems odd that oil should run forwards on a moving vehicle but it does on the Commando and the third fin is where the hollow gallery between the rockers converges. Strangely, even on a clean engine it can be nigh-on impossible to see the oil migrating downwards but once it puddles up and runs forwards, it can seem like a lot.

There are after-market alternatives to the odd rocker spindle retainers but it is certainly worth dismantling, checking for flatness and refitting with new gaskets.

Re: '74 Mk II, Still Chasing Significant Cyl Head Oil Leak

Posted by Ron Wellman at June 29. 2017

Previously alan_blackhurst wrote:

I had this problem last year. My fault hadn't emptied the breather bottle and the breather pipe was in the emulsified oil. I think that this caused the engine to pressurise. Which showed by leaking badly from the 3rd fin down. I have since fitted a non return valve in the breather pipe from the engine and make sure the breather bottle is emptied regularly. It hasn't leaked since.

Your problem maybe down to poor breathing.

Regards Alan

Re: '74 Mk II, Still Chasing Significant Cyl Head Oil Leak

Posted by Ron Wellman at June 29. 2017

Good suggestion Alan, thank you.

I have a PCV valve (works as a one way check valve)  on the line that comes from the transmission, right, side.  I'll remove the PCV valve to assure minimal crankcase pressure.

 

Now the big "Duh" on my part. The oil tank breather near the fill cap is blocked off and always has been for the two years I owned the bike.  That may be a huge part of why I have been unsuccessful in stopping the oil leak.  I'll run a hose off the breather and hopefully solve my problem.

Thanks again for bring up the poor breathing possibility.

Ron

Re: '74 Mk II, Still Chasing Significant Cyl Head Oil Leak

Posted by Ron Wellman at June 29. 2017

Previously richard_payne wrote:

Third fin up at the front is a favourite spot for oil to appear and the usual causes are either the inlet rocker cover gasket or the rocker spindle cover plates.

It seems odd that oil should run forwards on a moving vehicle but it does on the Commando and the third fin is where the hollow gallery between the rockers converges. Strangely, even on a clean engine it can be nigh-on impossible to see the oil migrating downwards but once it puddles up and runs forwards, it can seem like a lot.

There are after-market alternatives to the odd rocker spindle retainers but it is certainly worth dismantling, checking for flatness and refitting with new gaskets.

Re: '74 Mk II, Still Chasing Significant Cyl Head Oil Leak

Posted by alan_blackhurst at June 29. 2017

There have been previous post about the 3rd fin oil leaks. Just search the site for 3rd fin down

 

Regards Alan

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