Author Topic: Engine Failure at High RPM (Read 4612 times)

camelman · « **on:** February 21, 2010, 10:42:44 PM »

I have a '73 CB350F that I occasionally run up to 12k+ rpm (as indicated on the stock tachometer). I figured my main issue would be accelerated wear, but after talking to another forum member today, I realized a broken con-rod is a very likely scenario. So, I'm curious what kind of catastrophic failures people have seen, with which engine, and where they were in the rpm band when it happened.

I'll start it with a pretty minor failure. I passed 12,000 rpm with my engine during a passing maneuver and lost a cam follower on one of my point sets about ten seconds later.

Camelman

Terry in Australia · « **Reply #1 on:** February 21, 2010, 11:30:41 PM »

I've never destroyed an engine from mis-use, but I did seize my CB750K1 engine in 1981 when a dikkhead Triumph mechanic re-assembled it using silicone gasket sealant rather than nice new gaskets, and the craap blocked an oilway.

Of course, he also reset the valve timing one tooth out, so it was running like schidt anyway, but it put paid to my trip from Sydney to Melbourne, I was so p1ssed I pushed it around to a biuke wrecker and tried to sell it to him, but he was a great guy and calmed me down and said he'd look after it until I could find a truck to collect it.

I sent it back to Melbourne by train the next year and rebuilt the engine myself, under the tuition of a very knowledgeable friend, and rode that bike everywhere for another 4 years. I sold it to buy a Goldwing (POS.....) and still miss my old silver 750, and even occasionally dream of finding it again, sad bastaard that I am.........

Gordon · « **Reply #2 on:** February 21, 2010, 11:55:35 PM »

Quote from: camelman on February 21, 2010, 10:42:44 PM

I have a '73 CB350F that I occasionally run up to 12k+ rpm (as indicated on the stock tachometer).

If it's only occasionally and it's only a little over 12K rpm, I don't think you have anything to worry about. The redline for the 350 is pretty high to begin with, and as long as you're not keeping it over that for extended periods it's not really a problem.

One somewhat common result of a missed shift at high speed is a valve tappet adjusting nut loosening up and coming off, but that's usually only after pegging the tach needle, and doesn't normally result in any real damage.

Whaleman · « **Reply #3 on:** February 22, 2010, 04:24:10 AM »

Here is the #4 rod from a DOHC 750 my friend blew up after 40 minutes of WFO running with the engine low on oil. The DOHC had a problem with sucking air at high rpm. Found a ebay engine and am putting this new rebuilt engine in. He said the noise at over 100mph when it blew was intense. Dan

bryanj · « **Reply #4 on:** February 22, 2010, 09:04:07 AM »

That rod went cos a big end nut fell off (Betcha)

Honda rods dont let go on an unmessed with normally run (up to and even past red line OCAISSIONALY) engine

bistromath · « **Reply #5 on:** February 22, 2010, 10:27:15 AM »

Be interesting to see how accurate the stock tach is at 12K RPM, too. If it's anything like the speedometer, it's probably reading at least 10% high.

camelman · « **Reply #6 on:** February 22, 2010, 11:31:09 AM »

Bistromath,

Good point. Does that fancy grey box in your garage track rpm also? Maybe we could check the rpm accuracy one of these days.

Everyone else, please keep them coming. It is eye opening to see what causes failures in these engines.

Camelman

turboguzzi · « **Reply #7 on:** February 22, 2010, 11:57:46 AM »

Quote from: camelman on February 21, 2010, 10:42:44 PM

lost a cam follower on one of my point sets about ten seconds later.

Camelman

what do you mean by lost?

pics please.

revving the bejesus from your engine every now and then is actually good, it's called "Italian Tuning"

TG

camelman · « **Reply #8 on:** February 22, 2010, 12:53:08 PM »

I'm not italian, but I believe in their tuning techniques. I've always driven my vehicles hard, and have never had issues other than typical wear and tear.

To answer your question, the cam follower is the part of the point set that touches the crankshaft and get pushed up and down by the lobes on the crankshaft. That is what opens the points. It doesn't have anything to do with the camshaft.

Edit: I completely missed the "lost" portion of that response. The cam follower just fell off. I looked inside the cover for it, but it was gone. I have a funny feeling it just disintegrated into fine dust. It took me from a 350F to a 175T, and made my return trip much much slower.

Camelman

Jerry Rxman Griffin aka MuthaF'er · « **Reply #9 on:** February 22, 2010, 12:58:14 PM »

Broken intake valve head during missed power shift 1st to 2nd. Already at top of redline. HIGH rpm resulted. Valve floated. Valves don't like kissing pistons at such rpms. Obliterated the engine with aluminum bits from the exhaust to air cleaner. 75 CB750F.

Amphibious · « **Reply #10 on:** February 22, 2010, 02:17:55 PM »

Quote from: turboguzzi on February 22, 2010, 11:57:46 AM

revving the bejesus from your engine every now and then is actually good, it's called "Italian Tuning"

TG

Italian women should be treated the same way, or so they tell me

Terry in Australia · « **Reply #11 on:** February 22, 2010, 05:08:37 PM »

I bought my Laverda 750 SF1 from a guy who was such a fan of the marque, he married an Italian girl just so she'd translate his factory parts manual! She is truly gorgeous, (I met her when i came to collect the bike) but way too hot tempered for him, so he's divorcing her, and he sold me the bike because she's put him off all things Italian, forever.......... $:-\$

BLUE71TURBO · « **Reply #12 on:** February 22, 2010, 05:19:39 PM »

Quote from: Amphibious on February 22, 2010, 02:17:55 PM

Quote from: turboguzzi on February 22, 2010, 11:57:46 AM

revving the bejesus from your engine every now and then is actually good, it's called "Italian Tuning"

TG

Italian women should be treated the same way, or so they tell me

That's if you can get past the hairy arm pits and the bad body oder !!

BobbyR · « **Reply #13 on:** February 22, 2010, 05:30:52 PM »

Quote from: BLUE71TURBO on February 22, 2010, 05:19:39 PM

Quote from: Amphibious on February 22, 2010, 02:17:55 PM
Quote from: turboguzzi on February 22, 2010, 11:57:46 AM

revving the bejesus from your engine every now and then is actually good, it's called "Italian Tuning"

TG

Italian women should be treated the same way, or so they tell me

That's if you can get past the hairy arm pits and the bad body oder !!

Stay in So Cal. That comment here in NY could get you seriously injured. Hardcore Wops in these parts.

scottly · « **Reply #14 on:** February 22, 2010, 05:55:05 PM »

For what it's worth, I recall reading in a cycle mag years ago that the beginning of the red on a Honda tach is the max continuous RPM, and the end of the red is the actual max RPM, or redline. I had a friend with a 350-4 in the late '70s, and it was a revver. Camelman, what are the marks on your tach?

scooter1 · « **Reply #15 on:** February 22, 2010, 06:26:19 PM »

I had an 04 cbr600rr that I bought new....changed the sprockets for stunting...-1 in the front +10 in the rear...cruising to the stunt spot at 120km and BANG!!!!! Hot oil all over my leg and lots of smoke, my friends behind me thought my rear tire locked up!!!
The connecting rod came out the front above the oil filter and out the top side of the crank case!!! Only 12000km on the engine

scottly · « **Reply #16 on:** February 22, 2010, 08:30:31 PM »

Turboguzzi, I'm embarrassed for some of the anti-Italian statements here...
I've said it before, and I'll say it again, Webers are the finest carburetors ever made!
Scott

Gordon · « **Reply #17 on:** February 22, 2010, 08:39:47 PM »

Quote from: scottly on February 22, 2010, 08:30:31 PM

Turboguzzi, I'm embarrassed for some of the anti-Italian statements here...

I must be reading a different thread than you are... $:-\$

scottly · « **Reply #18 on:** February 22, 2010, 08:48:22 PM »

Then you missed the part about arm-pit hair and body odor, and WOP, a derogatory term for Italian that dates to Ellis Island, for With Out Papers. Sorry, just rubbed me the wrong way....

Gordon · « **Reply #19 on:** February 22, 2010, 08:57:41 PM »

Quote from: scottly on February 22, 2010, 08:48:22 PM

Then you missed the part about arm-pit hair and body odor, and WOP, a derogatory term for Italian that dates to Ellis Island, for With Out Papers. Sorry, just rubbed me the wrong way....

Apparently I did. That's what I get for skimming.

scottly · « **Reply #20 on:** February 22, 2010, 09:01:31 PM »

Hey, you're an honest prick, after all! Uh, let's just leave it at honest, ok?

turboguzzi · « **Reply #21 on:** February 22, 2010, 11:04:12 PM »

Quote from: scottly on February 22, 2010, 08:30:31 PM

Turboguzzi, I'm embarrassed for some of the anti-Italian statements here...
I've said it before, and I'll say it again, Webers are the finest carburetors ever made!
Scott

not even italian by birth, am a bit citizen of the world (have lived in four different continents so far, US included) and yet, yes, some not-so-smart comments up there. But it's OK at the end, makes you understand what some people's values and views are. Now I know better who to steer away from. The fact that we love SOHC's doesnt make angels out of all of us.

Thanks for paying attention.

TG

camelman · « **Reply #22 on:** February 22, 2010, 11:17:31 PM »

I hope that's the end of the questionable comments.

My tach shows redline starting at 10k and ends at 11k. The numbers go up to 12k.

Camelman

turboguzzi · « **Reply #23 on:** February 23, 2010, 12:53:29 AM »

yep, back to the subject

did see from up close a cb400 racer losing a rod, twice. not mine, just rode through the cloud of oil mist.....Very high state of racing tune and 500 cc mind you, but rods were always the 400's weak point.

the 350 motors share the same bottom end ( I think) but with much smaller pistons, should be safer at high revs.

Italian tunning has its logic. by putting a heavy thermal load on the motor and keeping the revs high, you dislodge carbon build up in valves, head and pistons.

in pre-catalizator days, i would take a car or motorcycle for a session of Italian tuning by night. after a few minutes youd spot through the rear view mirrors the carbon bits flaking of the motor and exiting through tail pipe, glowing in the dark.

Terry in Australia · « **Reply #24 on:** February 23, 2010, 01:29:41 AM »

Quote from: BobbyR on February 22, 2010, 05:30:52 PM

Quote from: BLUE71TURBO on February 22, 2010, 05:19:39 PM
Quote from: Amphibious on February 22, 2010, 02:17:55 PM
Quote from: turboguzzi on February 22, 2010, 11:57:46 AM

revving the bejesus from your engine every now and then is actually good, it's called "Italian Tuning"

TG

Italian women should be treated the same way, or so they tell me

That's if you can get past the hairy arm pits and the bad body oder !!
Stay in So Cal. That comment here in NY could get you seriously injured. Hardcore Wops in these parts.

It's alright Bobby, you're from a New York Italian/American family, you're a Vietnam vet and an ex-cop, and you're a top bloke, so you've got my respect mate, even if these guys don't recognize your self deprecating humor.

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Author Topic: Engine Failure at High RPM (Read 4612 times)