Look what happened here

[jmanz6]

I was trying to fix a stripped thread on one of my vlave cover bolts. I ran the drill into the hole and thought it went in awful easy but since the threads were pretty stripped out I didn't think much of it. Then, I ran the tap into the hole and after about 3 turns I noticed there was very little resistance. When I tried to back the tap out I heard a crack and then the tap just came out. Well, to my suprise, I found the boss on top of the cam bearing cap had cracked in half. Not good since I just spent $50 for a Helicoil kit to fix the damaged thread... Well, after taking the valve cover off, this is what I found...





Notice how much porosity is in the broken part. I know die castings are full of gas holes but HOLY CRAP that's bad. I am going to x-ray the cap at work this week and see what the rest of it looks like.

[Dave8338]

Not good. I agree, that is a rather bad casting.

[SqDancerLynn1]

When doing the cam cap you need to use a bottoming tap. Their is not enough depth for a reg tap
A drill press work great when worked BY hand. No electricity

[Billy Ricks]

I'll see if I have that cap on a head I have sitting around. Looks like the C cap. Lots of people will tell you you can't use one from another head but I have and never had a problem in thousands of miles.

[Billy Ricks]

I do have the C cap. If you want it PM me this evening. I'll be leaving town in the morning for a week so you would have to wait until I get back unless I pack it up tonight.

[jmanz6]

This cap was pre-cracked. I had noticed a snall chip at the top of the boss but figured it was from the PO stripping the threads for me. When I heard the crack I knew what it was and where it came from. Then it all clicked in my head that the thing was busted before I even tried to fix it. The drill bit never really took out the old threads because the hole just opened up when I put in the bit. The tap was a bottom tap that came with the Helicoil kit and it never really cut new threads because the boss was cracked and opening up. When I looked at the broken part I could see there had been a crak there previously and the boss had just fatigued to a point where it broke. Oh well, I found a head on Ebay to use for parts. Hopefully it will get here soon so I cna be back on the road. The riding season is short here in MI and I don't want to miss any more of it than I have (today).

[jmanz6]

Here are a couple x-ray images I took at work today with a micro-focus x-ray system and a CR plate. Notice the broken steel piece in the bottom of the hole, wonder if that is an old broken drill bit from during manufacturing? There are no threads on it so I'm not sure how it go there. Also, notice the porosity throughout the casting. I will be shooting the caps on the new head and choosing the ones I want to use as replacements. Hopefully none of them are pre-damaged too.

[Dreef1999]

I'll see if I have that cap on a head I have sitting around. Looks like the C cap. Lots of people will tell you you can't use one from another head but I have and never had a problem in thousands of miles.

I have seen mention of this a few times now. Is the reason to not mix parts from another head because of GD&T or is there another reason?

You could potentially install an out of tolerance part in your engine if you are not careful.

[Nessism]

No loss in trying the different cap but make sure you use plastigauge to judge clearance.

[gs1197]

"I have seen mention of this a few times now. Is the reason to not mix parts from another head because of GD&T or is there another reason?

You could potentially install an out of tolerance part in your engine if you are not careful."


The possibility of an out of tolerance part is there, but the main reason not to mix and match is because the head and cam caps were machined as a matched set.
Which means you COULD install a cam cap that was machined on the high side of tolerance on a head that was machined on the low side (or vice versa) and then have a tight/loose/misaligned fit.
Always check fit if you have to use a non-original cap.

[jmanz6]

I will definately plasti-gage it when installing it to make sure it's in spec. If it's not, then I will just install the entire head (UGH, that means pulling the engine out of teh frame and that means more down time). That 2009 V-Strom I rode yesterday is looking better and better...

[Steve]

... then I will just install the entire head (UGH, that means pulling the engine out of teh frame and that means more down time). ...

You don't have to pull the engine to remove the head.
You can remove the head and the cylinders with the engine still in the frame.

Is the reason to not mix parts from another head because of GD&T or is there another reason?

Please pardon my ignorance, but I have to ask ... what's "GD&T"?

.

[Kaiser Sosei]

GD+T = Geometric Dimensioning and Tolerancing

[Dreef1999]

GD+T = Geometric Dimensioning and Tolerancing

Yup. Just curious because factory work and fabrication is quite the mystery to me. The potential tolerance issues make sense but I wouldn't want to assume that there wasn't another issue at hand.

[duaneage]

Traditionally cam bearings should be Line Bored so they are precisely the same. In my opinion if reasonable results can be obtained within the range of torque specified, and verified with plastigauge, you should be OK.

This is acceptable because the cam has some wear and will allow tolerances to form.

Ask the racers in the Performance Tips thread area if better caps are made for this engine, maybe there are superior castings. You may have other parts that are marginal as well. It could be a bad batch of caps were installed. Or maybe not.