How much boost on stock rods

[LOYTOY]

Should try running the JE pistons, I think they work better.

haha yeah JE

 

[zebiraross]

It's not the rod bolts that get loose, it's the rod bearing that gets smashed, then the rod starts slapping, then it stretches the rod bolt, which loosens the nut, then failure... catastrophic failure.

I've caught the motor just as the motor started to tick, pulled it down to find this.

That is what I was saying. Just not going into the detail.

 

[zebiraross]

on first build on band new apex motor 30 km in. 17 lbs boost, strait vp c-111 fuel, stock rods & pistons with head shim- #3 rod let go from bottom end at 10500 rpm and fired itself right into the CR tunnel & cooler! Put band new motor in with carrilo rods & 10:1 GE pistons ran same fuel; didnt know any better; ran 20 lbs boost on pulls. 400km later heard a ticking sound while cruising at about 30kph, stopped shut it off. Pulled engine and the same #3 rod bearing had failed. Looked like it was getting no oil but I guess that is detination. Rebuilt again and run strait c-16 fuel 20 lbs boost with no problems. I'll never cheap out on fuel again!!

When you pulled the motor out the 2nd time did the pistons show signs of detonation?

 

[LOYTOY]

When you pulled the motor out the 2nd time did the pistons show signs of detonation?

I'm not sure... I dont know a lot about fourstrokes; I was told that detonation takes the rod bearing out first on a fourstroke. I just asumed that is what happened.

 

[zebiraross]

Your right about that. The other thing I was wondering is if your motor builder put in the right rod bearings with the Carillos and if he didn't match them up right and plastigauge each rod and main bearing with the right bearing that could of been your problem as well. These sleds have 3 different possabilities of rod bearings and sometimes engine builders don't know how to match them up right. Because with a stock rod you take it's number match it with the crank number subtract them and subtract another 2 to find the right bearing. So if the rod was a 4 and the cank was 1 you would 4-1=3 then subtract 2 = 1 and that is your number of rod bearing. Problem with Carillos is they are not marked with numbers so you have to make sure to plastigauge them and not just throw in a random bearing.

 

[Sapling-Thrasher]

Your right about that. The other thing I was wondering is if your motor builder put in the right rod bearings with the Carillos and if he didn't match them up right and plastigauge each rod and main bearing with the right bearing that could of been your problem as well. These sleds have 3 different possabilities of rod bearings and sometimes engine builders don't know how to match them up right. Because with a stock rod you take it's number match it with the crank number subtract them and subtract another 2 to find the right bearing. So if the rod was a 4 and the cank was 1 you would 4-1=3 then subtract 2 = 1 and that is your number of rod bearing. Problem with Carillos is they are not marked with numbers so you have to make sure to plastigauge them and not just throw in a random bearing.

Very good info!!

 

[LOYTOY]

Your right about that. The other thing I was wondering is if your motor builder put in the right rod bearings with the Carillos and if he didn't match them up right and plastigauge each rod and main bearing with the right bearing that could of been your problem as well. These sleds have 3 different possabilities of rod bearings and sometimes engine builders don't know how to match them up right. Because with a stock rod you take it's number match it with the crank number subtract them and subtract another 2 to find the right bearing. So if the rod was a 4 and the cank was 1 you would 4-1=3 then subtract 2 = 1 and that is your number of rod bearing. Problem with Carillos is they are not marked with numbers so you have to make sure to plastigauge them and not just throw in a random bearing.

HMMmm Wow I'm going to phone my engine guy right now! Thanks for that Info!!!

 

[BOOSTBONER]

stock rods are fine with arp bolts. Scott at diamond-smfg runs 27lbs on stock rods with arp bolts. I would recommend pistons though. Personal preference is the wiseco 10:1 with the oem rings from Mountain Performance. As long as you run good race fuel, like c16 or sumthin with a 110+ motor octane rating you should be good. It all depends on your fuel quality and compression.

 

[zebiraross]

stock rods are fine with arp bolts. Scott at diamond-smfg runs 27lbs on stock rods with arp bolts. I would recommend pistons though. Personal preference is the wiseco 10:1 with the oem rings from Mountain Performance. As long as you run good race fuel, like c16 or sumthin with a 110+ motor octane rating you should be good. It all depends on your fuel quality and compression.

Wiseco's are known to have crappy wrist pins that break. Ask Freak

 

[BOOSTBONER]

Wiseco's are known to have crappy wrist pins that break. Ask Freak

I have heard that, but like I said personal opinion. I have never had a problem with 'em. I like wiseco pistons.

 

[Remmy]

Unless Weisco has figured out the past issues I would stick with JEs. 10:1 compression will get you pretty good snap off the line while still letting you run 110 up to 20 lbs, depending on your elevation.

 

[IRONMAN]

HP will break rods, trust me but with a stock motor the rods will not be the first thing to fail from hp, the stock rods are very strong. Detonation is definatly the most comon reason for engine failure. Dont go off boost #'s to figure out hp, lots of guy run big #'s but look at the tail light of a sled well setup running alot less boost. Run good fuel and dont worry about your rods!