Hi I am currently doing up my 2011 sherco when looking around it i found a hole on the top head. It looks like a small bit of the top head has came off. Is this normal i could post a picture of it, if it would help. Any advice would be appreciated many thanks Dw.

A picture will help

here's  the picture

Looks like you have corrosion happening from the inside out. 

You might be able to patch it with some JB Weld or simalar epoxy, but first you should find out what is causing it

The head is aluminum and the bolts are steel. Looking at your picture their appears that rust is forming on the bolts. Their is probably electrolysis happening between the dissimilar metals (steel, aluminum) Usually antifreeze contains inhibitors to help control this but if water or weak antifreeze solution has been in the motor this could be what is aiding the reaction.

You should remove the head and find out the what the damages are.

Also, you should take a look at your water pump impeller/housing. If you are getting this type of problem corrosion it is likely that their may be problems with that too.

Note

 

You should apply penetrating oil to the bolts before trying to remove them as they may be difficult to remove and could snap or damage the threads in the head

The bike was also low on antifreeze

Edited June 18, 20179 yr by dwb5151

Are those the stock head bolts?

Ok I just looked at the Sherco manual. Definately not the stock bolts. Here's the problem, by not using stock bolts which may be stainless steel or at least a better grade of corrosion resistant steel you may have caused corrosion in your water jacket. Using tap water or non-premixed coolant will accelerate corrosion. Sorry to say this but you might want to pull the engine out of the frame for a proper tear down. Radiator flush is probably in order too.  

Good call Beta_Blocker

Edited June 18, 20179 yr by dan williams

The one thing which i don't understand is that the bolts on the other side aren't rusted and there the same type of bolt Could it be there  stainless steel?

I also checked the parts book your right there completely different type of screws. I just want to note that they are the screws which where in the top head when i bought the bike and i have had the bike for a couple of years. 

 

2011sparebook_trial_4T.pdf

Edited June 18, 20179 yr by dwb5151

Hmmm, usually not a good sign when somebody replaces critical bolts with non-standard items and they aren't stainless or titanium.

Just looks like a small casting flaw/ void from manufacturer that the paint or thin bit of aluminum may have chipped off of by looking at your pic. As long as there is not coolant leaking out of it, I would not get bent out of shape worrying about it, same with the head bolt material, its not a big deal ...just use oem recommended coolant and get out and ride  

Do not use stainless steel into aluminium thread (where galvanic corrosion have conditions to happen). It will corrode aluminium much more than zinc plated steel (like OEM are)

There are more galvanic potential between stailess steel to aluminium than zinc or steel to aluminium.

tip: If you put a multimeter tip into radiator water and another into you frame and see a reading of few mV. It's it. Change water and put antifreeze. 

Edited June 19, 20179 yr by cascao
foregin language issues

Thanks CASCAO. Learn something new every day.

http://www.ssina.com/corrosion/galvanic.html

Old bolts lost their zinc plated and become prone to galvanic "welding". So, inspect and discart these bolts if you feel that the are becoming stick sometimes. This happen on cars spark plug when people used to clean it with sand blast or wire brush.

On enduro motorcycĺes brake calliper bolts (yellow plated) is where I see it most. All of them seems like lost their beautiful yellow cover