Racing engines...what breaks most often?
 

Just curious for those with racing engines or who race...is there a component of the engine that breaks more often than others? From what I have seen and read, it seems the bottom end of these engines is usually pretty robust, rarely failing? If so, then would that mean valves/springs/cams would be the leader?

i would say its the wallet that takes the biggest hit

...sometimes catastrophically.

relationships, marriages,girlfriends etc.

The parts that break are the ones which you don’t have several spares sitting around for.:evilb:

Or not available until 6 months out.

Racing breaks:
Balls
Hulls
Outdrives
Valvetrain
Pistons
Rigged components

and everything others mentioned :)

Usually, it's the Loose Nut behind the throttles that causes the most problems.

You guys are too funny…but you are all correct… bajaman having raced supercat for a few years and being
directly involved in engine development, the valvetrain / camshaft are the biggest hurdles in racing that class. Things we’ve done included 55 mm roller cam bearings , truing up lifter bores. Bigger diameter lifters, various ramp designs on camshafts, using tool steel
camshafts, valvespring pressures , made own in-house rockers, used various retainers/ locks . The biggest helpful change was when we lowered the RPM to 7000 it helped stabilized it Speeds went down aiding in the safety of it. At the time I felt canopy construction was still lacking. Still loved the sound of the big block screaming at 7600 rpm kinda missed that.

when we had the spec motors in Stylin spinning 7400 valve train was the hadrest just as byrider said. Pleasure boat parts wont live in the race environment.
hope you're well btw!

I remember you guys You guys have a Marina.? Father and son team? And you are right valvetrains have certain harmonics at certain rpms best to to not stay at that rpm… been good keep watching the class do great 10-11 in kw pretty cool still have the boat like to run again soon


take care

you guys will love this vid how about .750 pushrods? i amazed at how much the valve stem moves we run jesel and big chiefs so i know that they break but never could figure out why!

Lol. That’s great. How true. Always wanted to go to a spintron to play with it. Cool stuff

Ego is a close 2nd.

High speed cams on valvetrain is wild. Never thought a spring would twist at the base to spring as the spring was compressed.

...and the moving of the stem. Wow.
​​​​
Mr. Murphy is always a co-pilot.

Valve springs

Guys,

The layman in me really want to believe that anything that helps a valve train in a drag engine survive at 10-11K RPM would be beneficial for a marine engine at 7500. Right?

Also... What's the theory on putting the clamp screw through the rocker shaft, rather than one on either side of it, with a saddle clamp? The machine designer/builder in me is cringing over that. A slightly longer shaft, with a near full-compliment saddle clamp would surely be more rigid than a hole through the ends of the shaft....? Been done? Curious...

Thanks. Brad.

those high speed videos are wild i never would have thought possible how much the spring is moving around i,m also shocked by how much the valve stem moves around and thats a very hard stiff piece of high quality metal

Boost,

I don’t know if it would cause more problems than it solved, but I could see upper valve stem guides incorporated into that rocker arm plate.

Thanks. Brad.

Awesome Videos
 

Thanks Brad for posting. From my vantage point as an ME from Dayton some great insight on Mechanical Engineering at the highest level. He even touches on the metallurgical side of the demonstration, which is where my career path lies. Very very cool.

Without going down a rabbit hole to nowhere.
10,000rpm for a 4sec pass
7500rpm for 2 hours.
You tell me what's harder on equipment. Its not so much the stability of the rocker arms (everybody basically runs TnD or some variant of them). As JD said above, its the harmonics of the whole package. Surfaced cleavers coming in and out the water, solid everything, so on and so forth create vibrations and harmonics that tear valve trains apart- especially at 7500. I had Richard Iskedarian tell me once that a bad harmonic in an engine can wipe a set of springs out in one dyno pull. Real Pro Stock guys have 3 or 4 different sets of springs for every engine. They run the ones that are "happy". Real race boat stuff is so far from pleasure boat stuff its insane. And then? You run the poor thing just as hard as you can for 1-2 hours. Our sport is one of the toughest there is on equipment. Period. Back when we ran 160 miles, you sandbagged as much as you could to save the equipment. These days its WOT flag to flag. Husker knows first hand how a 2.5EFI could tear its self apart at 8000 but live all summer long on a pleasure boat. And they dont even have valve springs lol.
Plus, people never realize (particularly car guys) boats are in 4th gear going up hill all day. No coasting. No shifting. Your car shifts way before 3500. 3500 is an easy cruise for most of us.

I was told by one of the 3 QC4V in the US that BBC wasn`t designed for marine use..the QC4V engines were designed for marine use from the ground up.
400 hrs on a 1100 is no problem.
Makes sense

5o years of racing
 

I know its an old thread and I'm a Newbie to the site but not to racing and its 2 things. Inferior parts and fatigue. That reaching to the smaller parts which is valve vtrain. Billy God old has spent. Any many hours when he was at ComP as researching this. Longer length rods apply more theust to the sides of the block and pistons tend to rock more because the shorter the rod the faster the piston travels within the same stroke. You can almost build a bulletproof engine, but it must be torn down often to refresh and replace parts.

A pro Mod in 20 runs is 100 seconds. Replace 1/4 of engine parts to prevent ent catastrophic failure.