Terrible failure!

[stargazer7467]

went out and logged 60 miles around indianapolis Sunday. Great time, went riding with a scooter group. Up until the last 1.5 miles tho lol. Looks as if i had a valve fail, the keepers and locks were still in place, but teh valve head on the intake broke off. Junked my ported race head , i was able to salvage most everyhting other than the head casting and piston. I was able to save the chromoly roller rockers, 28lb valve springs, billet keepers, and the valve locks. I saved the cam, and am going to use my spare block just to be safe. I rehoned it too. I have a question on teh billet rod however, it seems functionally intact but its beat up a bit on the top of the small end. Would this still be usable? Should i have it smoothed over a bit? Just not sure.

 

[Studeman68]

Holy cow! That is meltted down.... That thing got way too hot..cylinder temps got out of hand there.... I personally would not reuse that rod, and I would fatten the jetting up!

 

[ole4]

That looks like a hemi correct? You need to figure out why the valve head came off. First thought is what length rod were you using and that looks like a .009 head gasket. Is it possible you had valve to piston contact? Were you racing at the time or just cruising? What cam is in that motor? And if you know what was valve to piston clearance? It looks like it was the intake that broke so I doubt it was caused by valve float. The other causes could be bad valve or non concentric valve seating.

 

[noseoil]

I'm with Ole on this one. It looks like it hit hard enough to snap at the stem when it was open & then tumbled around when it was winding down. Do you know what kind of rpms you were turning when it snapped or what the top speed was?

I'm in the middle of a hemi build now & would like to know about the parts (cam, carb, gearing, speed, etc) & how much clearance you had between the valve & piston, deck height etc. when it was put together. Also, how old was the motor & how many high rpm runs (WOT) had it made?

 

[trinik7597]

First I have never seen 28# springs ... A hemi head with what roller rockers ?? What valves etc... If the hemi head is not worked for heavy springs and higher lift cam or ratio rockers making higher lift this failure kinda doesn't surprise me ..

 

[stargazer7467]

I wasnt racing , but was doing very spirited riding. This happened during an 8700ish RPM pull (I have a small digital tach). This setup had been great for 3 years. And i think they were 26lb springs iirc, not 28lb. I already run a bit rich as it is, i use a Mikuni TM22 with a 100 main jet. I am using the 6254 ARC rod 3.308" long. My deck height was flush. It is a Hemi engine.

The head was a prepared head, i did not build it. This bike is a ride, its seen sever high RPM pulls but averave was between the 5500 and 7500 RPM range. I unfortunately never measures valve to piston clearance, just rotated for contact. Being the locks and everyhting on the spring end was intact, im guessing that it was very close. I learned from this one.

I think i answered everyones questions.

 

[stargazer7467]

 

[stargazer7467]

Noseoil : I run a Black Mamba Cam, .275" LIFT 246 DURATION @ .050" 108° LSA, gearing is 5:1, Top speed recorded was 71MPH, max RPM recorded was 9400rpm

 

[trinik7597]

I didn't know it was 3 yrs old ... It doesn't owe you a dime !! Time for a rebuild

 

[noseoil]

Yep, sounds like you got your money's worth out of that motor. I figure the cam you started with is ok, but the rod, I wouldn't try it again in a new motor since it looks sort of beat up on the top end. Was it a forged piston or the factory one?

9400 rpm is getting a bit spooky, but it's nice to know it held together well enough to run for 3 years. Hope I have that kind of luck with the build I'm working on now. Were the valves stainless steel, or just the factory ones? Were they bigger than the standard ones (27 & 25) with bigger seats etc?

Good luck on the next build, want to see what you come up with for another motor.

 

[Phil1958]

i wonder how the push rod was bent. :confused1:

what kind of failure mechanism would cause that?

 

[FOMOGO]

i wonder how the push rod was bent. :confused1:

what kind of failure mechanism would cause that?

I would imagine that the loose valve head getting between the intact valve and the piston is what bent the pushrod. Just a guess but it makes the most sense to me.

Doug

 

[stargazer7467]

You're right it doesn't owe me a thing that motor was a champ it held up for a long time ,so I suppose we're even now since this is the bike that gave me half a titanium face. Lol

 

[noseoil]

"so I suppose we're even now since this is the bike that gave me half a titanium face. Lol"

I must be too new to the site, didn't know that one. When did that happen, is it OK & mended now?

 

[stargazer7467]

I can't just let her go , I have to rebuild her. You see, we've got history.

 

[stargazer7467]

https://www.oldminibikes.com/forum/mini-bike-discussion/117433-pin-striping.html

Thats a link to my Pinstriping thread, post #7 i talked about the festivities lol.

Everything seems to be ok now, i was discharged from the neurologist in April this year. Only reason i talk normal is because im a lefty, but things seemed to have rewired themselves nicely.

 

[noseoil]

Glad you came through it OK & that things are better now. Helmet & gloves is usually a good idea, but more if you're going faster or riding more aggressively. Summer riding, a toss-up between safety & heat I guess.

 

[ole4]

Wow just read that thread, scary what can happen, here in TX there are a lot of bicycle riders on the roads and when they fall its even worse as it is further from the ground. Glad that you recovered so well.

 

[stargazer7467]

Rebuilding! Picked up a new head, upgraded to 36lb springs. Did some talking to my vendor,Eric @ Studz in Michigan, looks like i wasnt using enough valve spring, fo rthe RPM i was usually running. Milled .050, also switched to a .045 fire ring headgasket. Plus a couple DIY pushrods. I free handed the pushrods within .005 of each other, i pretty happy with myself. lol

 

[tlizard2]

I need to check tomorrow to be sure, but I'm pretty sure you need about a 130 main jet for the 22mm Mikuni. Maybe someone else can chime in....