Jdeac Posted October 19, 2022 Posted October 19, 2022 Curious as to what can cause a head to crack around the plug holes and between valves. Pulled the head off pyro to do oil drain o rings and found this. Quote
Jdeac Posted October 19, 2022 Author Posted October 19, 2022 Also small cracks between inlet valves. Just under the green pencil marks Quote
Gixer1460 Posted October 19, 2022 Posted October 19, 2022 Its fairly standard on most multi valve heads - I'd hazard a guess that over 50% of any heads in use today will have some form of cracking. With the section of the metal present its inevitable! Quote
Jdeac Posted October 19, 2022 Author Posted October 19, 2022 2 have cracked all the way through the plug hole. That can't be right Quote
Fazz711 Posted October 19, 2022 Posted October 19, 2022 Seen this a lot and never seems to be a problem. Most have pulled head off for some other reason and found to be cracked. Quote
Swiss Toni Posted October 19, 2022 Posted October 19, 2022 Common fault on pre-unit Triumphs. Ran just fine all the same. Quote
Jdeac Posted October 19, 2022 Author Posted October 19, 2022 So is this OK In a turbo engine. Running 20psi approx 320bhp and 120 octain race fuel?? Is my next question Quote
Gixer1460 Posted October 20, 2022 Posted October 20, 2022 std. disclaimer - insert here - Yes! Alternative question 'how are you going to fix them - if you want them fixed? . . . . . . . Swap the head to another 'less cracked' or one that will crack? Quote
Jdeac Posted October 20, 2022 Author Posted October 20, 2022 Got you. Just something I've not seen/heard about before. Quote
clivegto Posted October 20, 2022 Posted October 20, 2022 Seen it on dot heads and was surprised that they still run alright. Weren't cracked as bad as that though. Quote
gsxwill Posted October 20, 2022 Posted October 20, 2022 If she was running fine before she will still run fine!! Difference is you now know the head is cracked, only question is can you live with it or will it nag at you from the back of your mind Quote
Jdeac Posted October 20, 2022 Author Posted October 20, 2022 I personally think its worse than in the pics. And yes it was running alright I guess. Never had a turbo bike before. Let alone a drag bike so..... who knows Quote
Jdeac Posted October 20, 2022 Author Posted October 20, 2022 @gsxwilleverything bothers me. Just a case of if I can sort it or not. Life head bikes work etc etc Quote
gsxwill Posted October 20, 2022 Posted October 20, 2022 @Jdeacfunny how life changes, riding and messing with bikes used to be the one thing I never worried about,but like others have said lots of heads have small cracks, obviously photos don't always show how bad they are! Maybe pressure testing the head?? Quote
Jdeac Posted October 20, 2022 Author Posted October 20, 2022 Been to local shop. The said scrap. But also met someone and a family member Who is mad into the building are favorite oss machines. Quote
Duckndive Posted October 22, 2022 Posted October 22, 2022 I was chatting with someone at the weekend who chucks an obscene amount of Nos into GSX motors when i said how do the cracks in the head take that his response was when they get really bad we have to put even more in and then find a head with smaller cracks "there cheep" The fix on a drag bike is a skulled head ...but not a cheep exercise ... i stuck 20 psi in my drawthru without any dramas Quote
imago Posted October 22, 2022 Posted October 22, 2022 39 minutes ago, Duckndive said: IThe fix on a drag bike is a skulled head ...but not a cheep exercise ... I imagine the cost of the bronze would be eye watering these days let alone the machining. Quote
Duckndive Posted October 22, 2022 Posted October 22, 2022 1 hour ago, Jdeac said: What is a skulled head??? https://www.dragbike.com/race-machine-hayabusa-combustion-chamber-skull-installations/ ignore the bus reference its applicable to all 2 Quote
Gixer1460 Posted October 22, 2022 Posted October 22, 2022 There used to be a video on Youtube (I think) or maybe it was hosted on Ian Kings Dragbike site showing the full process done by Brian Johnson in his shed - that guy had skills beyond his facilities - Respect! As skulls go, that's quite a slim one and pretty high compression as there is virtually no chamber to speak of! Quote
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