Hole blown through crankcase

Bike is a 1980 KZ750-4. I am pretty sure overfilling the engine with oil was the cause. I just put CR Special 29mm carbs on and got the bike running mint, air/fuel ratio was good checked plugs heavily throughout tuning process so i the bike was running like a beast real nice. I topped off my oil when it was getting low i checked the glass, i overfilled it so that there was a TINY bubble of air in the sight glass with the engine 100% cold. After rides i would notice the engine really really abnormally hot at the same time i noticed the sight glass was full without any space. I know im an idiot but we all have to learn somehow right? I commute with the bike so i was too lazy to drain the oil out. On my way home with the bike fully warmed up today i was merging onto a highway and 8k rpms is when she popped and the oil light went on, thankfully an exit was near by. and upon inspection there is literally 2 holes punched out in front of the crankcase on the front side of the motor. heres why i believe it was not air/fuel ratio related and also why i believe it was too much oil (built up too much pressure especially with high performance carbs) : The bike fires right up with no abnormal clunking or anything, infact it sounds exactly the same, firing on all 4 and sounds real strong and good actually, If the bike was running too lean and popped the engine i dont think it would still be able run like it is able to now, and the plugs would have looked atleast a little bit whitish, infact they were all dark brown. What do you guys think? Do you agree with me that the overfilling of oil created so much pressure with the combination of the new CR Carbs that at 8k rpms the crankcase had no where to put the pressure except through a hole in the front of the crankcase? The bike still runs and fires right up so there is no piston problem i know for sure, and im currently in search for a new engine btw.... Does anyone know of any other engine that will slip right in? Any comments? I Know guys i deserve to be shot :sick:

Pictures do speak volumes...

KZ 650 or KZ 750 engine will bolt right in. I put a '82 GPz 750 engine in a '77 KZ650 frame. No mods to engine case or frame.

It seems that the pressure would blow off through the crankcase vent. There's one sure way to find out. The motor will have to come out, unless you want to get really creative with JB Weld.

Kapahulu wrote: It seems that the pressure would blow off through the crankcase vent. There's one sure way to find out. The motor will have to come out, unless you want to get really creative with JB Weld.

+1
Dont claim to be an "Expert"....but it would seem to me that unless your crankcase vent is stopped up, excess oil would "Vent"???? I guess that would depend on how ...."Overfull" it is, I know on my '75 Z1-B 900..have occassionally overfilled it to top of glass and never had a problem, Mine seems to "Vent" the excess.
Ed

It certainly sounds like a weird problem, but I doubt that it was caused by a bit too much oil because the breather vents crankcase pressure. I have filled mine to the top of the glass many times and have never had a problem even when running it up to the 9000 rpm redline. Folks who have put an excessive amount of oil in their bikes generally report oil pumped through the breather into the airbox. I have never seen any report of excess oil damaging an engine case. I would suspect before that happened it would blow oil out through engine seals, breather, etc. It seems to me it would take an awful lot of pressure to blow out a chunk of an engine case. Ed

Pic?

Maybe just hit something in the road?

Good Fortune!

Start by pulling the oil pan and get back to us. Im really doubting the oil level caused the failure.

Taking pics if I can get the darn bike home its about 15 miles away from home. I will definitely pull the pan and see if there's something there. Maybe someone left a bolt in there or something . The crazy thing is that there are 2 holes. I'm honestly gonna attempt to brake clean and roughen the entire surface and layer some jb weld after everything is addressed who knows I might need new cases...
p.s.
Anything timing related would have blown a piston too right? What narrows a lot of this down is that the bike starts and still runs strong. However I'll 100% get back to you guys when I take pics of the bike when it's home I'm not sure if it rides which i know is different from running. Thanks for all responses thus far oh and i noticed the bike did sputter a little before popping, but this wasn't the first time it sputtered

If you figure out what caused it and correct that you should be able to have someone weld the holes up as long as they don't impact a boss inside the case. Ed

depending on where the hole is and the size I.
on smaller holes that don't have to carry much load or have a sealing surface I would drill it out and thread it and plug it whit an bolt + some hardcore Loctite thread lock.
some rivet the bolt (I don't since I don't like beating on aluminium)
anyway drill, tap and bolt.
it way safer method than welding since aluminium easily warps when welded.

If you want to make it look nice you could grind the bolt flush whit the case after the Loctite have hardened.

Regarning riverting the bolt. (I don't recommend it for aluminium)
Same method as above but you thread the bolt in some more (about 1-2mm will do)
cut it of leaving about the same on the other side.
then a big sledgehammer as an anvil on one side of the bolt and a big pen hammer on the other (round end)
tapping the bolt so it mushrooms, flipping the case over and mushroom the other end as well.
The risk is.
1, you miss and strike the aluminium and probably take of a good chunk.
2,overexpanding the "rivet" causing the case to crack (I have never experienced this)
3. losing your anvil so the force goes through the aluminium instead, most likely cracking the case.

Next method (soldering) (will be almost as good as welding if done right but still a chance of warping)
take a pice of metal and make file it so it will fit the hole.
clean up the hole (no sharp corners) and do everything you can to give the solder as much surface area as possible, then use silver solder.
(youtube it since it is hard to explain)

But regarding the hole in the case we need some pics.
And I hope you don't even think about turning the motor over without oil.

Best regards H

I doubt it was excess pressure. If you had enough pressure to rupture the engine case the engine would have been leaking oil all over the place, the crank seals, output shaft, valve cover, cam plugs etc Plus it would be forcing oil past the rings and it would have smoked terribly.

Either something inside let loose and broke the case or your front tire kicked up something on the road and smacked the engine case.