VF backfire, valve cover seal blown out

Anyone have an idea on what would cause a backfire in the head of an '85 1KR and cause the valve cover seals to blow out? Motor has always run well and did a quick 10 mile trip, then sat for about 15 minutes. On trying to restart, it immediately went bang, big puff of smoke from the motor and I found the valve gasket blown out around the #3 cylinder and a little around #2. Motor still turns over normally and sounds mechanically ok, I didn't start it obviously with the gasket blown out. Pulled the valve covers and everything looks ok up top.

I'm guessing fuel but from where? Intake? Back through the exhaust? I never did a valve check so I don't know if they're off but the motor sounded fine. Any thoughts?

Sounds to me like you're gonna need to check the valves, but then again, I've never heard of that happening either... :blink: I hope it's not too bad! :unsure:

[image: View Post]vfrcapn, on 15 May 2010 - 02:36 PM, said:

I'm guessing fuel but from where? Intake?
Crankcase? Do a compression test, maybe a stuck piston ring.

Will check the valves and do another compression test. It seemed like a carb backfire but I'm not just getting the connection between that and the valve gaskets being blown, unless the guides are shot? The air filter and box look normal, no sign I can see of being blasted.

Funny thing, this happened as I was about to load it up in to a buyer's truck. He had done the test ride and I had the cash in my pocket. Needless to say he changed his mind.. :pissed:

Sounds like a small crankcase explosion.

We have them periodically on our large Clark and Cooper cas compressors at work. Sometimes if one cylinder isn't firing, some of the mixture from that cylinder can work it's way into the crankcase, especially if the rings/piston/cylinder is worn.

If the cylinder is firing intermittantly, sometimes it can trigger a crankcase explosion. Oil mist is quite flammable, which can also cause or contribute to the problem.

There are actually large vents in the manways of our big engines, covered on the inside with gasket material, and if the crankcase pressures up and has an explosion, the gasket material tears and lets the pressure out so it does no damage to the engine.

Then of course, oil starts pouring out onto the floor, which is another story......


These aren't our units, just random internet pics, but you get the idea:

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[image: View Post]vfrcapn, on 15 May 2010 - 03:10 PM, said:

Funny thing, this happened as I was about to load it up in to a buyer's truck. He had done the test ride and I had the cash in my pocket. Needless to say he changed his mind.. :pissed:


WHAT? He broke it???

[image: View Post]SEBSPEED, on 15 May 2010 - 05:50 PM, said:

[image: View Post]vfrcapn, on 15 May 2010 - 03:10 PM, said:

Funny thing, this happened as I was about to load it up in to a buyer's truck. He had done the test ride and I had the cash in my pocket. Needless to say he changed his mind.. :pissed:


WHAT? He broke it???

No, just really bad timing. He handed over the cash and then we did the test ride, I rode the VFR, and took him on some local roads. He was sold but when we got back and I went to fire it up to walk it in to his truck, bang. It was never out of my sight and he didn't do anything to it, just crap luck for me & I had to hand the cash back.

So compression says 167-176psi across all 4 cylinders.

Intake valves are all within spec along with most exhaust valves, a couple exhaust are a little loose. (.17mm vs .14mm spec, ok?)

Never heard of the crankcase explosion but seems to fit. I dunno, I'm going to button it back up and see how it goes.

(Seemed like a decent guy, hopefully he'll join up here. He's got a '98 VFR and a garage full of various sized dohc Hondas.)

Oh I missed the part about the sale going bad.

Sux to hear, sorry.

Veefer800Canuck, on 15 May 2010 - 07:16 PM, said: Oh I missed the part about the sale going bad. Sux to hear, sorry. Just reading about crankcase explosions, this seems to be mainly a diesel engine issue? Are all your engines at work diesel, I assume? I guess it could have been worse...

Dayum!!! That aftermath looks expensive!

Back on topic, make sure your crankcase breather isn't kinked or blocked.

[image: View Post]hawkrider, on 15 May 2010 - 10:17 PM, said:

Back on topic, make sure your crankcase breather isn't kinked or blocked.

Thanks, it's on the list to double check.

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[image: View Post]vfrcapn, on 15 May 2010 - 07:41 PM, said:

Are all your engines at work diesel, I assume?


Only the "little" 900 hp emergency generators are diesels.

Siamesed 450HP Silver 92 Detroit diesels that are twin supercharged AND twin turbocharged.


The BIG engines are all powered by natural gas.

Single turbo two-cycle V-10s making 2200HP and 35,000 ft/lbs of torque @ 330 RPM(yes, that's thirty-five thousand at three hundred and thirty RPM).

Also single turbo two-cycle inline sixes and inline fives making 2000hp and 1800hp respectively @ 300RPM.

Plus a bunch of smaller 4-cycle inline-8 naturally aspirated engines making about 650hp, plus a bunch of big electric drivers from ~650 up to 4500hp.

The coolest ones are the turbines. We've got them from 1100 to 1300 up to the really big boys @ 5000hp out of what is essentially a jet engine.

All back together and running just fine. :cool:

You might have had a airbox explosion during start up that pressurized the crankcase through the vent tube which caused the the seal to blow...

[image: View Post]vfrcapn, on 16 May 2010 - 11:23 PM, said:

All back together and running just fine. :cool:


Now to call the buyer back... or do you think you scared him off? :unsure:

[image: View Post]BusyLittleShop, on 17 May 2010 - 01:54 AM, said:

You might have had a airbox explosion during start up that pressurized the crankcase through the vent tube which caused the the seal to blow...

Larry, the crankcase vent tubes go from the head, through a collector box and back to the airbox. Do you think it could have generated enough pressure through all that tubing to pop the gaskets?

[image: View Post]SEBSPEED, on 17 May 2010 - 05:25 AM, said:

Now to call the buyer back... or do you think you scared him off? :unsure:

I think I'll put some miles in it and make sure it's good, and see if I want to keep it. ;)

Scary stuff alright!! I was there when it happened!! All that smoke..!!! I thought it was a fire. Left with the money but not sure about being scared away just being............thoughtful at this point. After hearing the theory of oil mist explosions i did some didgging around in the net. This seems like a logical thought. The bike has the top oiler which may have caused some degree of misting and being in one of the hotest parts of the engine a flash would seem to make sense BUT as near as I can figure there needs to be a spark?? I am wondering about some sort of trapped vent from the covers? I have not necassarily lost intrest but also interested in making sure it was freakish occurance not a regular part of the startin proceedure!! LOL. keep in touch Mike all is not lost. You have my email and here will be hit and miss as I usually hang out at the 11f site. Grump aka Mike.

Welcome to the site Grump! :fing02:

Welcome Grump, with that list of bikes you'll fit right in here. :fing02:

I'm leaning towards Larry's (BusyLittleShop) idea that it was a backfire through the carbs/airbox. The vent tube is open from the airbox to the head, through the oil collector box. Probably lean on the idle side, judging by always needing choke to get it started up. I'll order some new jets this week.

Well, at least it didn't "break" anything, so you have another chance to get it running good and hopefully no repeat performances.

[image: View Post]vfrcapn, on 17 May 2010 - 10:37 AM, said:

I think I'll put some miles in it and make sure it's good, and see if I want to keep it. ;)


Ahhh, now I see what happened. Subconscious sabotage! You probably told someone that you needed to sell it but deep down you were thinking otherwise. Brilliant, an explosion that doesn't do any damage but loud enough to scare off the buyer. For future reference, please tell me how you did it. :biggrin:

[image: View Post]Kel, on 18 May 2010 - 05:31 AM, said:

[image: View Post]vfrcapn, on 17 May 2010 - 10:37 AM, said:

I think I'll put some miles in it and make sure it's good, and see if I want to keep it. ;)


Ahhh, now I see what happened. Subconscious sabotage! You probably told someone that you needed to sell it but deep down you were thinking otherwise. Brilliant, an explosion that doesn't do any damage but loud enough to scare off the buyer. For future reference, please tell me how you did it. :biggrin:


he knows taco bell gives him a 1/2 hp "boost"
and added a beritto to the gastank with with some FIRE sauce in an atempt to a full 1 hp added to the bike... clearly this bike had some heart burn and let it out both ways. :goofy:

Thanks for the welcome guys, much appreciated. It's a nice bike and I watched it all along and am still interested if it's OK. And it would be going to a good home where it wouldn't be left out in the cold, put away wet or otherwise mistreated!!I'll hang in a bit longer and see what happens.