Author Topic: Should I be worried (cracks in head)? (Read 6582 times)

Noddy78 · « **on:** April 16, 2015, 09:25:33 PM »

Thoughts?

scottly · « **Reply #1 on:** April 16, 2015, 09:31:25 PM »

Yes, those cracks are a problem. Time to look for a new head or a good welder/machinist. New head would probably be cheaper than repairing....

Don R · « **Reply #2 on:** April 16, 2015, 09:31:34 PM »

Yes it's time to worry, the crack can loosen the seat and cause it to drop not to mention the obvious compression loss / broken part falling into the engine.

Stev-o · « **Reply #3 on:** April 16, 2015, 09:41:47 PM »

I wouldn't be worried, I'd be lookin for a new head.

SOHC4 Cafe Racer Fan · « **Reply #4 on:** April 16, 2015, 10:03:04 PM »

Time for a new head.

Noddy78 · « **Reply #5 on:** April 16, 2015, 10:13:52 PM »

#$%*, that's what I was afraid of. Surely the machinist should have picked those up when he was lapping the valves and installing the new guides? Looks like I've got some yelling to do...

brandEn · « **Reply #6 on:** April 16, 2015, 10:19:38 PM »

Time to find a new machinist.
seriously...

Retro Rocket · « **Reply #7 on:** April 16, 2015, 11:19:46 PM »

Quote from: brandEn on April 16, 2015, 10:19:38 PM

Time to find a new machinist.
seriously...

And a refund, what an arse...

lrutt · « **Reply #8 on:** April 17, 2015, 04:21:11 AM »

never seen cracks that big in a head before. wow.

evanphi · « **Reply #9 on:** April 17, 2015, 05:50:37 AM »

Quote from: Retro Rocket on April 16, 2015, 11:19:46 PM

Quote from: brandEn on April 16, 2015, 10:19:38 PM
Time to find a new machinist.
seriously...

And a refund, what an arse...

If they didn't see it, stop work, and tell you about it... they probably caused it!

Stev-o · « **Reply #10 on:** April 17, 2015, 07:25:15 AM »

Quote from: evanphi on April 17, 2015, 05:50:37 AM

Quote from: Retro Rocket on April 16, 2015, 11:19:46 PM
Quote from: brandEn on April 16, 2015, 10:19:38 PM
Time to find a new machinist.
seriously...

And a refund, what an arse...

If they didn't see it, stop work, and tell you about it... they probably caused it!

That brings up a good question: what would cause cracks such as those?

flybox1 · « **Reply #11 on:** April 17, 2015, 07:34:45 AM »

heavy handed with the valve seat cutter maybe?

your only hope might be that you've got a few good 'before it went to the machinist' shots of this area $:-\$

754 · « **Reply #12 on:** April 17, 2015, 07:51:02 AM »

I was going to ask if it had compression, as I recall an old dragbike single that had cracks like that but ran fine. I think though on my Ducati single , it was blowing back thru the intake when it cracked.

I got a 750 72 750 head that has two seats that look like the sealing surface. Of the seat sunk down about 1/8 inch..not sure what happened there.

I am not not thinking of any scenario where working on it could have caused that.

madmtnmotors · « **Reply #13 on:** April 17, 2015, 07:58:45 AM »

Almost looks like the piston struck the spark plug.

calj737 · « **Reply #14 on:** April 17, 2015, 08:01:44 AM »

I was going to say it looks to me as though the seats are the source. Widest crack begins on both seats, then travels to plug hole. Also upper seat looks chipped where it approaches the lower- Be interesting to hear from Mike R on his opinion to cause and recommendation.

iron_worker · « **Reply #15 on:** April 17, 2015, 08:19:14 AM »

What bike is this off of that has valve seat inserts?

I would definitely be looking for a new head. You could have it welded but I think with the time that it would take to do it properly in prep, welding, and machining you would $ ahead to just get a new one.

IW

PeWe · « **Reply #16 on:** April 17, 2015, 12:05:52 PM »

I have no experience at all regarding head damages. But I can find others with help of Google.
I found one other case where the reason was said to be overheating. Lean carbs, not closing valves or late ignition?
http://georgiajag.com/Documents/HeadArticleJCNA07/XKHead.htm

I'm happy that my cb750 head did not crack when I melted a hole in a piston back in the days, rods bluish in the upper end. Also close to crack my head 4 times when I was much younger, a few stitches each time

LesterPiglet · « **Reply #17 on:** April 17, 2015, 12:33:40 PM »

That seat is definately farked and there is another small crack between the seats as well.

Noddy78 · « **Reply #18 on:** April 17, 2015, 02:57:54 PM »

Great, thanks for the replies guys. Follow up question, they installed new valve guides in this head, if they remove them again are they useable in another head, or are they a once-only type deal? This is the best 'before' shot I've got - looks to be cracks there already, but I asked them to see if they coud fix the rusting on the valve seat, so that's the same cylinder:

Also, if we're trying to figure out what happened, bear in mind these also came out of the same engine:

calj737 · « **Reply #19 on:** April 17, 2015, 05:42:43 PM »

Yeah, I would not jump to the conclusion that the machinist is responsible for the damage of that head. I think we all agree a new head is in your future. Just make sure it fits your cylinders and not your hat size!

BPellerine · « **Reply #20 on:** April 17, 2015, 05:43:26 PM »

cam towers must have gotten loose at one time,maybe due to stripped threads and the whole thing was floating around rubbing on cover.bill

Retro Rocket · « **Reply #21 on:** April 17, 2015, 06:09:11 PM »

Quote from: calj737 on April 17, 2015, 05:42:43 PM

Yeah, I would not jump to the conclusion that the machinist is responsible for the damage of that head. I think we all agree a new head is in your future. Just make sure it fits your cylinders and not your hat size!

I think the damage was originally there, the machinist needs his head read for doing the seats on that head....

PeWe · « **Reply #22 on:** April 18, 2015, 03:15:08 AM »

Is the cam ear really welded? This indicate a series of severe events, or is it one only that cracked head and broke cam?
I remember that kind of cam damage and found the thread.
http://forums.sohc4.net/index.php/topic,125377.msg1424921.html#msg1424921

LesterPiglet · « **Reply #23 on:** April 18, 2015, 05:33:31 AM »

Ive also had a cam like this. The owner broke it peening the bolt. $:-\$

Lostboy Steve · « **Reply #24 on:** April 18, 2015, 06:39:51 AM »

Wow. That's a good one....

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Author Topic: Should I be worried (cracks in head)? (Read 6582 times)