Blew the head gasket on the front cylinder the other day. What are the common causes of head gasket failure?

 

I don't know about common causes, but not letting the motor warm up enough before getting on it hard can cause it.

 

studs pulling out of the cases,were h.bolts loose?we made a long spacer to make sure the studs/h. bolts would take the proper torque.could just be gasket failure too,check for warpage and use cometic gaskets on reassembly
kirby

 

Chester and pro drag pretty much have this one covered !!

 

on the few evos ive pulled down, the head bolts are usually loose, id pull it down and like prodrag says, use cometic. also cometic uses a different torque procedure than whats in the book, i torque all my motors down to 50 ft/lbs using cometic gaskets.

 

50 ft/lbs is too much for stock hd evo cases
so be careful, as you will crack them on the lifter side
42 for stock compression is more than enough, and a lot safer
you should only use 50 with SnS cases or similar
there is no common cause as such, but not warming up is a good way to do it
I have seen no evidence to suggest that evo head bolts are commonly loose
in fact, they are typically quite tight to break free, as they tend to lock onto the studs
so you can not really tell what clamping pressure they were exerting
now evo studs that are broken, that is not unheard of
if you do the job well, with good gaskets, you can expect a good service life
I really like the james metal base gaskets, and think their head gaskets are fine as well
but personal choice wont affect the result as long as you use good quality

 

on my 90 it was a front stripped head bolt, a heli-coil and back on the road. i believe i torqued mine to 40 psi.

 

Some already gave you good answers. Did you just have some work done? Anything recent that could have caused this? It really depends on the situation prior to it happening.

 

I did experience some unusual behavior prior to the gasket failure.

I had been at my local indy shop to get new tires and brake pads, and while there the mechanic asked me about my plugs. We had discussed the plugs some weeks earlier, as he was saying that the literature with the Spyke ignition calls for a gap of 25 - 30 as opposed to the stock gap of (I'm guessing here) 38 - 40. I had put several thousand miles on a set of Harley gold plugs that were gapped at around 40 with no issues - the bike ran great, in fact so good that I went way beyond the recommended 5,000 miles on the plugs.

So when talking about replacing them, he brought up the gap issue again. I had replaced the plugs a little while back with some NGK Iridiums that I gapped around 38. At the shop he suggested changing the plugs to Harley plugs, and gapping them tight as per the Spyke recommendation. So I gave in, he gave me two brand new plugs gapped at 25. I got about five or six miles down the road when I started losing power, and suddenly got misfires. I was almost home, so I just kept going, managing to make it into the garage before it crapped out completely.

The only thing that had changed was the plugs, so I pulled them and saw something I'd never seen before - it looked like the electrode had melted, and a little piece of it was extended out so that the two terminals on the plug were almost welded together! I still had my old worn out Harley plugs (gapped around 40) sitting there in the garage, so I threw them back in. I restarted the bike and it ran normally. I went for a short ride, less than an hour (it was getting dark and the temps were dropping into the 40's) just to see if the problem would reoccur. It didn't. I called the shop the next day and told him about it, but he didn't have any ideas, and I don't think he really believed me until I showed him the weirdly ruined plugs last week.

So a week later, I took off for a ride and was out for a few hours with no issues. In fact at one point I was briefly on the highway and was keeping up with traffic moving at 70+. On the way home, again just a few miles from home, the gasket blew. At first I heard something a little funny and thought maybe my front exhaust pipe was coming loose. Then suddenly the thing went completely, with sparks and smoke blowing out. Uh oh. This time I didn't make it home, and had to pick the bike up with a trailer.

So that's why I asked about the common causes of gasket failure, as the whole sequence seemed a little strange to me, and I was wondering what the real cause of the problem might be. I was thinking that maybe the blown gasket might be a symptom of some other problem, and that simply replacing the gasket wouldn't resolve it in the long term.

 

OK, the melted electrode is a sure sign that your spark plug tip got way too hot, probably due to pre-ignition that can be caused by a number of things. One being a blown head gasket. Having said that, the plug you put in there may not have bee the right heat range. As yours melted, you would need a colder plug. It may be one of timing issue. I think the simplest thing to do is change your gasket out. While you are in there, check out your combustion chamber and condition of the cylinder walls.

I'm not familiar with the Spyke ignition, so I can't comment on the spark plug gap. .25 is just too close. Normal recommendation is .40. Good luck and let us know what you find out.

BTW..nice bike, I have a 1989 FLHTC. She and oldie, but goodie.


dave