What Gives.3 Motors Locked Down

[nastynotchback1]

well 3 weeks ago we had one motor go bad.Changed it out for the spare motor that was pretty much stock and ran the race with that.couple of days later he was ridden it with that motor and it locked up.I blamed it on the gas and mixed a new batch.I pulled the stock motor and installed new crank and bearings along with a billy holt ported top end.he rode it all last week and all seemed fine.today we got to the track and he was going out for some prerace practice and dogoneit the motor locked up tight.Couple of guys there told me it was probably because i am running 110 octane gas and i am not doubting them but it ran 50 laps last weekend on the same gas with no problems.this is an air cooled motor.anybody gotany other ideas why i keep locking the motors up? i got a stage 6 w/c motor being built and i don't want to screw that motor up too if its something i am doing.thanks

[THARNESS]

What type of oil and what ratio? Have you checked your jetting? Mabye you're too lean. Were these motors fresh or did they have alot of time on them.
We run Bel-Ray H1R and 32-1 ratio. Many poeple run a leaner mixture but I like the extra oil.

[nastynotchback1]

Originally posted by THARNESS
What type of oil and what ratio? Have you checked your jetting? Mabye you're too lean. Were these motors fresh or did they have alot of time on them.
We run Bel-Ray H1R and 32-1 ratio. Many poeple run a leaner mixture but I like the extra oil.

first and third motor were fresh and the second was just a stock motor we use as a back-up.i run maxima synthetic smokeless oil at 40:1.i checked the jetting last night and it was perfect.nice tan plug and installed a new plug.this was at about 65 degrees and it was pretty much same temp out side today.already decided to change the brand oil i use but i am wondering if it is not a timing issue.we put about 50 laps on this motor last weekend with no problems in practice and today made 1 lap.

[MAXRPM]

If jetting oil ratio etc. is all correct you may look at replacing the carburetor. OKO carburetors were famous for doing that, ran great for a short or long period of time then all the sudden it would lean out and seize the engine. If it is timing it would generally melt a hole in the top of the piston versus seizing cylinder wall or crank etc. The top of the piston would also be dished on top where it was melting before it actually blew a hole in the piston. If there is no issue with the top of the piston you could rule out timing. The higher octane fuel will run cooler not hotter than pump gas.

[nastynotchback1]

Originally posted by MAXRPM
If jetting oil ratio etc. is all correct you may look at replacing the carburetor. OKO carburetors were famous for doing that, ran great for a short or long period of time then all the sudden it would lean out and seize the engine. If it is timing it would generally melt a hole in the top of the piston versus seizing cylinder wall or crank etc. The top of the piston would also be dished on top where it was melting before it actually blew a hole in the piston. If there is no issue with the top of the piston you could rule out timing. The higher octane fuel will run cooler not hotter than pump gas.

i sent you a pm.thanks

[Ryko racing]

wE RAN STEEL CYL AIR COOLED CVTS FOR YEARS.

AMSOIL 2 CYCLE 32 TO 1, SUNOCO 94 PREM MIXED WITH VP C 12 50 / 50

OKO 24 MM CARB NEEDLE MIDDLE, STK PILOT, 128 MAIN

32 RACES NEVER AN ENGINE FAILURE.

SOUNDS LIKE YOU ARE LEANING OUT .( IF THE CARB IS WORKING CORRECTLY AND THE MAIN IS CORRECT CHK THE NEEDLE.LEAN IN THE MID RANGE WILL COOK EM FAST.

200 PSI COMPRESSION, PVL IGN,

[nastynotchback1]

pulled the plug this morning and its nice and tan but it has a piece of metal lodged in it under the strap.gonna tear into the motor late today or in the morning.if i move the clip down that will richen it up?its in the middle now on a d-slide 28mm with 130 main.

[Logan #34's Dad]

Originally posted by nastynotchback1
if i move the clip down that will richen it up?
Right!

[nastynotchback1]

well it lost the wrist pin bearing and bent the rod,tore up the cyl,and broke the piston.

[travis rimmer]

we run vp 114 high octane 40 to 1 and have had no problem

[Ryko racing]

im not an engine builder but i think the lower rod bearing went thus the piston hit the head and destroyed the wrist pin brg.

On our cobras when we burn rod bearings we are lean in the midrange( clip).

if you burnt the rod bearings in both motors it is probably the lean condition.

richen the needle and fatten the main for your test runs and do frequent plug checks.( its easier to start them rich and go backwards) AND CHEAPER TOO.

GOOD LUCK. IF YOU ARE NOT SURE AND HAVE ACCESS TO A DYNO I WOULD RECOMMEND TRYING IT AS IT WILL SHOW THE LEAN CONDITION BEFORE YOU DO DAMAGE.

[lilman]

i"m not a builder either but have you checked for bad case seals or anything like that it sure sounds like something is leaning them out i agree with ryko its way easier and cheaper to start fat and slowly go back as plugs a cheap in comparison i have seen carb boots and reed cages become delaminated even slightly and leak air in as well ,lost two sled motors this winter as a result. went directly to damons quad and redid all gaskets around the carb and reeds.

[nastynotchback1]

this motor was practically new.it had new crank bearing and seals,crank,piston rings all gaskets everywhere and new head/cyl.Justin from max rpm and i have come to the conclusion that i was turning it was past the ability of a 10pin crank.it was seized up because a roller from the wrist pin bearing was lodged between the cyl wall and piston.This motor was not lean.the plug looked good and always has.

[lilman]

well i really feel for ya! it sure can be a struggle somtimes with these little mods ,but is very gratifiying when it all comes together after all the hours we put in them to watch them pull holeshots,good luck and have a safe year.

[nastynotchback1]

Originally posted by lilman
well i really feel for ya! it sure can be a struggle somtimes with these little mods ,but is very gratifiying when it all comes together after all the hours we put in them to watch them pull holeshots,good luck and have a safe year.


Thanks and same to you

[zach R 7x]

not trying to start anything here,but what did your engine builder say about the motors?

seems like you got a major problem here, whether it was inferior parts or something else , the same problem with 3 motors would bother me.

[nastynotchback1]

I am the engine builder on 2 of these(that could be the problem lol) one was a stock bottom end i put a cyl and head on.Justin @ max rpm has become my engine builder from this week forward.After 3 conversations about these motors we came to the conclusion that i was spinning the 10pin cranks past what they should have been and they are just flying apart.I am relatively new to this sport and didn't know that there was a 10 and 12 pin bearing. this last motor had a malossi full circle crank with a billy holt ported arisal cyl and head combo.it had pretty good a/c parts in it but owell.

[Full Throttle00]

I would change the carb out like Justin recomended, OKO= no good.
Even though the plug looks nice and tan, we had went through everything with similar problem, changed carb (28m D slide Koso).

BTW what compression are you running?

Some fuels & mixtures can cause build up (carbon, unburned fuel, oil) on piston head and create additional compression which I was told could lead to failure. But can also break loose some of this hardeded crust and possibly create a problem .:eek2:

We ended up running Amsoil Dominator 75:1 with 107 Trick fuel (220 compression head) for 1-1/2 years with NO catastrophic failure, tons of holeshots, & wins on a 70cc air cooled motor.
Hope this helps