OHC gasket leakage

[TheLegend]

Hi guys,


I have an 2002 CB 750-Sevenfifty, RC 42, 15.000Km(~9000 miles) and since last autumn I've had a small leakage at the over-head cylinder lid gasket. Now the moto stays in the garage(winter here) and I've found an 10' oil spot on the floor. Do you have an explanation or happens to someone? I've buy a gasket and I will fit it, but I need an advise why. Some help please.

[sgtslag]

Try searching the Internet for factory recalls for your bike, first.  If you find some, make sure your bike has been repaired; if it has not, then check with your local mechanic shop to see how to go about getting the recall work done -- should be free to you, they would be paid by Honda.

Not familiar with newer 750's, but the older one's suffered from excessive heat.  Heat causes rubber, and cork, gaskets and seals to harden, become brittle, and break.  The older, air-cooled engines, like my '79 CB750K, run at the limit of the oil's thermal breakdown point, around 250 F, under heavy loads.  That kind of heat, over time, will cause the seals, and gaskets (cork and rubber) to harden, etc.  Back in the 70's, many owners installed oil coolers to alleviate some of the thermal stress (mine dropped the oil temperature from 250 F, to ~210 F, with almost identical engine load conditions).  There are a few adapters still available to allow an oil cooler installation on the older 750's, but I have no idea about options available for your bike.

Without installing an oil cooler, your options are limited (replacing the gasket is assumed).  Over time, you may notice that the gasket on the header wears out after the same number of miles, and you will have to plan to replace it at that time, every time...

Try changing the oil every 1,500 miles/~2,500 km.  This won't prevent damage to the gaskets and seals, but it will reduce engine bearing damage by replacing broken down oil with fresh, before the thinned oil can damage your engine (assumes standard dino oil, not synthetic, which will last longer before breaking down).

There is a non-petroleum based additive which softens rubber gaskets and seals, without damaging them over time.  I have used it successfully in multiple cars, and motorcycles.  It is not a miracle, but it can soften rubber elements in your engines.  It is called AT-205 Re-Seal.  It is available from Amazon.com:

http://www.amazon.com/ATP-Re-Seal-8-oz-AT205/dp/B000NVW1LM/ref=sr_1_1?s=automotive&ie=UTF8&qid=1297460723&sr=1-1

The AT-205 Re-Seal will not help with cork gaskets, but it will help with any rubber O-rings, or seals.  Just follow directions, and add it to your crankcase oil when you change it.  Leave it in until you change the oil again.  One treatment should work for a year, or more.  Stay away from petroleum-based rubber conditioners, as they will soften rubber for a while, then possibly dissolve them over time.  This product won't harm rubber, period.  Used it in all of my vehicles, a couple of years ago, without any detrimental effects -- only positive results from it.

Try locating Internet forums specific to your bike model and year.  There likely are forums dedicated to your bike model, where this forum is dedicated to older 750's.  Such a forum should be able to offer you much better information, as they will be familiar with your newer bike.  Cheers!