Board index Flathead Power-Technical Questions, Answers, and Suggestions 45 Flatties Another Head Gasket Failure

Another Head Gasket Failure

Moderators: Curt!, Pa

Post Thu May 08, 2014 10:40 pm

Posts: 530
Location: Ogden, Utah, USA
I had the same problem a while back. Ran a tap into the bolt holes and then blew a head gasket on a mountain ride. So after more looking, found carbon in the bolt hole at the bottom. Tap went in, bottomed and I missed the build up at the bottom. Some time with a scribe to get it loose and, a bottoming tap cleaned it all up. The gasket will fail if it is not clamped well. All of the above suggestions are good just a thought on why it fails in the same place.
Steve H

Post Sat May 10, 2014 10:00 am

Posts: 470
Location: Six miles East of Cheney, Wa.
I suppose there has been 1,000 studs vs. bolts threads, but it does seem like studs would be the way to go. I really think that next winter when I de-carbon my heads (and probably "lose" a little compression) I might do that.

Enigmas, did you make your studs, or purchase ready-mades? Again,, seems like with studs and nuts, and good greased washers, the head is going to clamp down better. ?

I'm thinking that even because in the old days torque wrenches weren't commonly used on the flathead twins, "logic would dictate" that one would want to use them today. Never hurts to be more precise if possible. Having said that, I'll admit that I didn't use one on the Little Mistress, but I did make sure bolts were tightening correctly, and none were too long. I think that usually, if one has a very good sense of feel when it comes to nuts and bolts, a bolt that is bottoming out will feel different. ?? Maybe not. I suppose that once the engine is in the frame, and the tanks are on, it can be a little difficult to get a torque wrench on the bolts...I know I have to use a couple different wrenches and sockets to get to all of mine.


Post Sat May 10, 2014 4:02 pm

Posts: 783
Location: Victoria, Australia
I live in OZ and purchased the studs from a vintage and classic HD supplier called Pacific HD Trading but this was about 12 years ago. I'm sure that many of the businesses known to this board and probably closer to your locale could assist with a set of studs.

If you decide to go for the studs you may find that the cyl heads are difficult perhaps impossible to remove with the engine in the frame. (It's been a while since I've had mine apart and can't recall removing the heads in the frame with the studs in place)

When you torque the bolts ensure you have thick (& large diameter) washers in place to not only spread the load but to also distribute the tension evenly to the head seat. Use some engine oil on the thread and under the nut to reduce friction as you torque the head.

As an aside, I've always use tension wrenches on cyl heads.

Post Sat May 10, 2014 10:25 pm

Posts: 1604
Not so much a 45 thing, but the old BSA M series sidevalves were well known for blowing at the head joint, especially if you had fitted a later alloy cylinder head to an older WD model and not changed the head bolts at the same time. The general belief that you could always keep a blown gasket in service a bit longer by applying more tension, plus the extreme operating temperatures meant that stretched head bolts were commonplace; cast iron engines were pretty much immune to over-tightening and corrosion would form a better seal than any gasket!
Shoot, a man could have a good weekend in Dallas with all that stuff...

Post Sun May 11, 2014 8:36 am

Posts: 301
Location: Ohio
This is a great conversation and I’ve learned a few things that I’ll pay closer attention to next time I have to remove them. You guys got me so fired up about these gaskets that this morning I went out and figured I’s start tearing mine down. I feel like an idiot now because I may not have a head gasket failure after all.

Last week when I saw this, I figured it was another gasket failure.


Today on the rack, I noticed this. The mess is coming from the drain plug. At least I hope so for now. :)


Post Mon May 12, 2014 6:52 pm

Posts: 470
Location: Six miles East of Cheney, Wa.
Well anyhow...yes one would have to make sure one could still remove the head with the engine in the frame. I think I have plenty of room for that, (see photo) as long as the studs were no longer than needed. Oh oh...have I sinned by posting a big twin on the little twin forum? Sorry about that!

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Post Tue May 13, 2014 1:26 am

Posts: 1604
The BT is a flathead engine in a frame which also accepts OHV engines so it probably isn't an issue. The 45 is a different beast altogether. My Ariel-framed project bike certainly wouldn't allow head removal using studs either
Shoot, a man could have a good weekend in Dallas with all that stuff...

Post Mon Jun 30, 2014 2:36 pm

Posts: 222
Location: Virginia

I torque the head bolts to 65 ft lbs on my engine test stand, then run the engine till hot, cool and retorque twice. Sometimes the torque goes down to 45 ft lbs between cycles


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