NooB Alert: At what point in engine mods should you weld the block for strength?

[unixphreak]

New to the modded thumper lawn engine scene,but have been in the motocross and RC nitro buggy scenes forever. I just was wondering at what point in the mod process should you start welding the block and cylinder areas of these engines to keep them from becoming hand grenades?

I have basically a stage 4 212 sitting on my bench that I am sure would benefit from a balanced crankshaft but would like to know when it would be worth my while to get it welded.

Thank you for everyones assistance in advance!!!!

 

[JTSpeedDemon]

I don't think it's as much of a concern for a Predator 212.
Briggs flatheads need it once things get crazy with cams and high RPM.
I wouldn't do it unless someone knowledgable tells you to.
Carsandcameras built a Stage 4 P212, and I don't think their lifter area was welded.

 

[Dingocat]

John and Ike aren't the perfect example here though, as in "it'll be fine"

 

[BigWes]

John and Ike aren't the perfect example here though, as in "it'll be fine"

Exactly what he said above.

Those two clowns are constantly scrapping engines all the time...one wonders why...NOT...

If you are into stage 4 you are at the point of time and money to consider block braces at least. You're making enough power and torque to twist the small crankcase under load depending on how you push it. I wouldn't hesitate at all to consider investing some time into beefing up the bottom around the crankshaft. All you may need is just a good billet side cover...I don't know what you got going or even what would be best suitable for your application. Some of the racers around here are well versed in keeping the high power Mills together.

 

[unixphreak]

Sorry I forgot to mention that I do have the ARC billet side cover on this engine. Since I have invested a bit of money, I really wanted to ask this question to keep this running as long as it can.
this is going into a Trailmaster MB200 right now, but would possibly get transferred to a kart when I find a suitable chassis.

Thank you for the information mentioned above.

 

[Randy H]

A couple things to consider are RPM and piston to head clearance.

What's your intended max RPM, cam profile is a big factor here. What's your piston to head clearance?

In other words what you can run at 7000RPM might result in a two piece block at 8500RPM. Parts stretch.

.030" is a number I'm comfortable with. Many aren't happy if the piston isn't kissing the head.

 

[Flyinhillbilly]

I run a hemi predator block 9000+ every other weekend with no bracing and a billet sidecover. I’ve broken blocks before, but this one has been hanging tough all year. I think the side cover has a lot to do with that. I have .027 piston to head clearance. I also think tune has a lot to do with keeping them together. Preignition, more commonly know as spark knock, will create some crazy cylinder pressures and break almost anything.
That said, I’m working on my motor for next year which will be based on the tillotson reinforced block for peace of mind.

 

[unixphreak]

I think this one is approx .020 and a .010 head gasket. No milling has been done just the addition of a flat top piston. the cam I have is good to 7500 and I have 22# springs so it should be good to that RPM or float just short of that. Stock valves for now though upgrade to higher grade in the future but not any oversize ones also stock rockers for now with more durable billet in the future. Would staying with 1:1 suffice or would 1.2:1 or 1.3:1 be worth the price?

@flyinhillbilly: I was looking at the Tillotson, the block looked super clean and the casting iw way better than the predators

 

[Flyinhillbilly]

I’m very happy with my tillotson block, I can’t wait to torture it

 

[KartFab]

If you are going to spend enough money to need a welded block, you would get more bang for your buck from this https://www.jrracecar.com/jr-billet-animal-block-1-tall-deck/

Unless you are a machinist, or know one that knows how to machine things, you shouldnt' even attempt to weld a block yourself (even if you can). Too much can go wrong (warping). If you do weld it, you need to get it welded 1st, then de-stress in an oven, then get machine work done. It will be all sorts of warped no matter what.

 

[unixphreak]

thank you, I have not heard of those before, very very cool.

 

[unixphreak]

Looks to be now I am having issues with my carb setup. I have the newest 212 with 27mm intake and 25mm exhaust. My carb is a 24mm flatslide genuine Mikuni with 130 main, 15 pilot, 5N13 needle and the 454 stock emulsion tube. I can get it to idle and have a nice brown color, but when i chop the throttle it wants to stall out. I don't have any resistance on it except the TC since I am waiting for new shocks to set the chain length. Would anyone have an idea where I am failing? Also I forgot to mention earlier that I have a .265 cam, cr-mo pushrods, billet lifters and heavy duty cylinder studs.
I have read the rule of thumb is two or so sizes lower than you r intake valve is about right for the carb size or will i still need to hog out the head?

The only things i have not done is SS valves/valve job, brass guides, ratio rockers, porting and crank balancing besides any crazy stuff like longer stroke or bore. Generally bolt on solutions.

 

[KartFab]

try the 140 main and 20 pilot Thats what I use, everything else stock. If it is stalling when cracking throttle, you might just need to adjust needle height. Also, i like to get my idle a bit rich, so it doesnt lean up when i crack throttle.

 

[unixphreak]

I dropped the needle all the way, so I will try the 140 main. Thank you for the advice.