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Cure for oil leaks from head?
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Post new topic   Reply to topic    Honda305.com Forum -> Motors - 247cc | 305cc | 337cc | 350cc
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bfd402
honda305.com Member


Joined: 16 Sep 2003
Posts: 48

PostPosted: Thu Feb 18, 2010 8:13 am    Post subject: Cure for oil leaks from head? Reply with quote

Is there any solution for what I believe is dreaded leaky cylinder heads as described in the Bill Silver books?
THis particular head is from my vintage race bike and has only about 4 weekends on it. It is the head only as the rest of the motor is freshly assembled and very clean. As it heated up I was getting oil around the spark plugs(both sides) and it seemed to also be leaking around the exhaust ports as the headers were constantly covered. I'm swapping heads currently but would like to save this one if possible since it's in good shape. Good spares are getting tough to come by.
Could this be ill fitting valve guides allowing oil around them and seeping out below?
thanks
Bill
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LOUD MOUSE
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Joined: 15 Aug 2005
Posts: 5455
Location: KERRVILLE, TEXAS

PostPosted: Thu Feb 18, 2010 8:59 am    Post subject: Re: Cure for oil leaks from head? Reply with quote

I had a bad one years back and tried the HONDA cure to no avail. ........................lm


bfd402 wrote:
Is there any solution for what I believe is dreaded leaky cylinder heads as described in the Bill Silver books?
THis particular head is from my vintage race bike and has only about 4 weekends on it. It is the head only as the rest of the motor is freshly assembled and very clean. As it heated up I was getting oil around the spark plugs(both sides) and it seemed to also be leaking around the exhaust ports as the headers were constantly covered. I'm swapping heads currently but would like to save this one if possible since it's in good shape. Good spares are getting tough to come by.
Could this be ill fitting valve guides allowing oil around them and seeping out below?
thanks
Bill
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teazer
honda305.com Member


Joined: 08 Feb 2010
Posts: 769
Location: Midwest US

PostPosted: Thu Feb 18, 2010 9:37 am    Post subject: Reply with quote

Bill,
As you know, the CB 72/77 have a cats in iron skull. Sometimes there is a slight gap between the skull and the head and oil seeps out.

Any 350 conversion will tend to leak - I have built several and they all weep to some degree or other and usually around the plug.

If you have more than a slight mist, it sounds like a weep through the gasket or maybe one of the front stud dowels is missing or loose.
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bfd402
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Joined: 16 Sep 2003
Posts: 48

PostPosted: Thu Feb 18, 2010 12:17 pm    Post subject: Reply with quote

Teazer
Currently this is still on original size bore, I haven't made the jump to 350.
The oil is coming out from the upper part of the head, I think migrating past the skull. Who knows, perhaps those little galley plugs? The cylinder barrel is dry and both of those dowels are in place.
Its enough oil that the entire head looked like it was spritzed with a spray bottle after a practice or race. It could be cleaned but wouldn't pass a visual inspection at pit-in.

I was hopeing there was a trick that never made it to the Silver manuals, in LM's bag of tricks for example, but I guess not. THis head would probably be fine for a street bike, it's first couple of outings were fine too. Just started the middle of last season.
Thanks for the input
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teazer
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Joined: 08 Feb 2010
Posts: 769
Location: Midwest US

PostPosted: Thu Feb 18, 2010 2:54 pm    Post subject: Reply with quote

There are a couple of things your could try. One is to try to peen the alloy around the plug to mechanically fill the gap.

You could also take the head off and clean it first and then try to get a high temperature loctite to wick in through capilliary action.

You could also try a smear of JB weld around the plug insert and see if that holds the tide at bay for a while.

Most race motors sweat a little, but that sounds like it's more than that. A light spatter won't be an issue though at pit in.
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LOUD MOUSE
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Joined: 15 Aug 2005
Posts: 5455
Location: KERRVILLE, TEXAS

PostPosted: Thu Feb 18, 2010 10:54 pm    Post subject: Reply with quote

Or ya could get a different head and trash this one and chances are your problems will be gone. .......lm



teazer wrote:
There are a couple of things your could try. One is to try to peen the alloy around the plug to mechanically fill the gap.

You could also take the head off and clean it first and then try to get a high temperature loctite to wick in through capilliary action.

You could also try a smear of JB weld around the plug insert and see if that holds the tide at bay for a while.

Most race motors sweat a little, but that sounds like it's more than that. A light spatter won't be an issue though at pit in.
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mike horvath
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Joined: 25 Apr 2009
Posts: 208
Location: chino hills, ca.

PostPosted: Fri Feb 19, 2010 12:00 am    Post subject: oil leak Reply with quote

This may sound elementary, but might the oil be seeping out around the cylinder head side covers? Oil will tend to collect on the plug base as well as weep onto and drip from the header studs.
Just my thought.
Mike
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