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jojo1224

Should I be worried?

18 posts in this topic

I blew the head gasket on my yz444f during my last ride well today I started to pull the engine apart and here is what I found. Sorry for the crappy pictures they are from my blackberry.

Here is the problem:

l6xKVh.jpg

Here is just after removing the head:

x0Tseh.jpg

Started to clean the piston and found this:

dYWtCh.jpg

Closer:

6j5Wlh.jpg

And closer:

ugX6Hh.jpg

Here is the head after a light cleaning:

TdmoWh.jpg

Nice shiny intake valve:

C85aSh.jpg

What do you think? Should I just put a new head gasket in and ride or should I start replacing parts? I also checked my valves and my intake valves are at .10mm and my exhaust valves are at .15mm.

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Personally, I wouldnt tear down an engine that far without installing a new piston and ring kit. I wouldnt see a problem reusing that one in a pinch though assuming it was within spec or low hours.

However, me being a detail nut I would also install new stainless valves and valve seals as well. Thats just me being me. My friends say I take things too far when repairing stuff though.

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The piston appears to have been in contact with the head, which probably means the fit to the cylinder is too loose, and that could be from wear or the fact that it was fit wrong to begin with. The other possibility is that your rod bearing is loose. Either way, you need to check into the matter.

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I may be wrong but by any chance did the blown part of the head gasket coincide with that spot on your piston? I have seen many head gaskets blown on cars and in the cases where the gasket was blown leaking into the combustion chamber the piston showed similar patterns.

Like Grayracer said I still would measure the cylinder/piston/ and check the lower rod bearing for excessive side play indicating possible lower bearing issues just for your peace of mind. Couldnt hurt to clay test the piston to head clearance either. If all checks out well and the you believe the piston and head are contacting you could probably get a thicker head gasket or base gasket to increase that clearance.

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Ill take off the cylinder and check the big end bearing, and maybe order a new piston and hone the cylinder. I am not going to do the valves because they are new with less then 25 hours on them, I will re-shim the exhaust valves though.

@Bobbed06 I can't tell where the head gasket started to leak because there isn't much left of it.

piston looks like its dirty from dust if you wanna replace it go ahead but it should work

Its not dust, I just took the head off last night and you can feel it.

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Damn it, I just pulled off the cylinder and the plating is worn through in one spot, it looks like it got something between the cylinder and piston. But my bottom end checks out, there is not up, down play and a very small amount of side to side. So time to get my cylinder replated and to buy a new 97mm high comp piston. There goes my pay check tomorrow.

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Damn it, I just pulled off the cylinder and the plating is worn through in one spot, it looks like it got something between the cylinder and piston. But my bottom end checks out, there is not up, down play and a very small amount of side to side. So time to get my cylinder replated and to buy a new 97mm high comp piston. There goes my pay check tomorrow.

The coolant that gets inside the cylinder can really hurt the oils ability to lubricate which may have caused the plating damage. Regardless it is good that you pulled it down farther for inspection. It would have been a waste of time and money if you wouldnt have.

Grayracer said that the piston/cylinder had issues a few posts back. Grayracers on point :ride:

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use loctite superglue on the gasket and glue it to the cylinder to stop pieces flying out just a tip for those old engines keeps them holding well

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So time to get my cylinder replated and to buy a new 97mm high comp piston. There goes my pay check tomorrow.

Before you go out and get your cylinder replated, consider a new cylinder. Here's one on E-bay for $262 shipped from ncyyam :

http://cgi.ebay.com/ebaymotors/YZ450F-06-09-OEM-Yamaha-Cylinder-NIB-2S2-11311-10-00-_W0QQcmdZViewItemQQhashZitem45faea10a3QQitemZ300562387107QQptZMotorcyclesQ5fPartsQ5fAccessories

There's someone else selling them cheaper, but a quick look at their feedback gives you a good idea as to the type of seller the other guy is.

A new sleeve will more than likely cost you around $80 - $100, plus labour. For an extra few bucks I'd be inclined to go new. Just my $0.02 :ride:

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use loctite superglue on the gasket and glue it to the cylinder to stop pieces flying out just a tip for those old engines keeps them holding well
"Super glue", or any other cyanoacrylate adhesive is completely unsuitable for use on any head gasket.

In the first place, YZF's don't lose pieces of their head gaskets (note that there is nothing missing from the one shown). Secondly, the YZF head gaskets are coated with their own bonding sealer, and are supposed to be assembled dry and clean. If using an aftermarket gasket that lacks this coating, or if the surface is suspect in some way, use K&W Copper Coat, an actual head gasket sealer.

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Before you go out and get your cylinder replated, consider a new cylinder. Here's one on E-bay for $262 shipped from ncyyam :

http://cgi.ebay.com/ebaymotors/YZ450F-06-09-OEM-Yamaha-Cylinder-NIB-2S2-11311-10-00-_W0QQcmdZViewItemQQhashZitem45faea10a3QQitemZ300562387107QQptZMotorcyclesQ5fPartsQ5fAccessories

There's someone else selling them cheaper, but a quick look at their feedback gives you a good idea as to the type of seller the other guy is.

A new sleeve will more than likely cost you around $80 - $100, plus labour. For an extra few bucks I'd be inclined to go new. Just my $0.02 :ride:

This is for a YZ426F not a 450. I haven't called but there is a company in my province who is an affiliate for US Chrome. So I will see if I can drop off both of my cylinders (my old 95mm from old motor and this 97mm) there to get one bored and replated and the other they can buy off me or work something out.

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