How reliable are HD flatheads

[Norrimichlson]

I have read all sorts of things about the flathead on the internet, but most of it was just articles and stuff and from my experience people writing those often times don't have a clue what they are writing about.

In general I have a feeling that the flathead is often forgoten, everybody just talks about the OHVs, I would say 99% of the builds i see are OHV bikes. Are Flatheads any good? I mean the moco built them for like 41years and didn't change to many things. Looking at the inside of those engines, I find them very simple, the 4 cams remind me of the sportster. Over all I can see nothing wrong with them, even tho I never owned ore rode one, of course. But somehow i keep reading that they are bad and unreliable engines and that is what i believed for a long time. Then i saw a video of pacific mike on YT, he was about to rebuild a 80ci flathead and he said, ''they have big heavy flywheels and once the start going down the road they don't really want to stop''. Since then I am somehow intrigued by them and really wanna know the truth.

MIke

[JBinNC]

When new, the flatheads were reliable because of their simplicity. The big twin flatties were widely used by urban police departments for that reason. But, we are three generations away from those times, and all these old bikes are, well, old.

The 45 has good parts support because of all the spares manufacturered for the war effort. Also because the second world war spread the 45 across the world, there is a good aftermarket parts availability worldwide.

The big twin flatties don't have that kind of parts support, so owning one is more of a challenge.

Keep in mind that the flatties are SLOW, by modern standards. That does not necessarily make them less desirable as vintage motorcycles, but all day at 80 mph on the interstate is not in the cards. (I could say the same about my shovel FLH. It gets buzzy and uncomfortable over 70 mph or so.)

Just my 2c,
Jim

[DoomBuggy]

My very first Harley was a flatty 45 that I got from our mailman in exchange for painting his barn. It was a basket case and even as a 15 year old kid ( with a shitload of help from my Dad ), I was able to put it together and get it running. They are really basic to work on and damn near indestructible, but as pointed out they are not terribly fast. ( Still a heck of a lot cooler than a 125 Honda )

[Norrimichlson]

Thats what I thought looking at it more closely. A rigid old piece of american steel pretty straight forward tech, but lacking power. I am not really looking for something fast, althogh I think imma be looking for a bigflat. Parts are kinda expensive but you gotta spend your money somehow, so...

[docmel]

Really, parts for 45s, at least motor/tranny, are cheap. In just WLAs alone, about 33K were made, with enough spare parts to literally build almost 90K more. And up until 1975 or so the servi cars were still being made, and 90% of the parts would fit WLCs, WLs, and servi-cars. Lotsa parts sources out there I had a stock WLA, and it was VERY easy to start, idled great, easy to wrench, but top speed was about 50 or so, limited to the tranny and sprocket ratios. I agree, not allot of power, but what a great motorcycle

[Guest]

The Harley WL 45 flatherd in my book is one of the greatest bikes EVER built,
they are bomb proof, they refuse to die & will run forever, almost infinitesimal rebuildable wherever you are in the world,
if I had the choice of riding around the world on ANY motorcycle out there, I would choose a 45,
it wont let ya don but if it does it's fixable, it's fast enough but not so fast ya don't see where ya riding,
very simple to work on, in my book, EVERYONE should own one at some point in their life,
now they aint the fastes bike out there, but ya dont need to do much to make them a bit better round town but 70mph is about the most you'll get reliably without much dinero being spent on race parts,
me, I like plodding along & if I wanted to go fast I'd have got something else.......BUY YOU A 45 & HAVE FUN FELLA !!

[CDeeZ]

Not sure how I missed this thread until just now.

I have a BTSV 80 incher. It was my dad's. Hole melted in one of the pistons maybe 11 years ago and I took it upon myself to rebuild the engine personally. It was a project that got put on the back burner many times because of life, and the fact that I have a tendency to take on a shit ton of projects anyways.

I consider myself to be fairly knowledgeable on the flathead HD's at this point. I've had the motor in and out of the frame and built and torn down more times than I care to admit while I was struggling to rebuild the engine myself. But I finally got it sorted out, and I'm glad I took the long road home with it instead of taking it to a shop. These motors are so old now, a lot of shops may not really know what they're doing on one. Some of those shops may also not be willing to admit that. Also, it's worth mentioning, that MOST of the difficulty with me rebuilding my own big twin flatty is the fact that I didn't just put it back to stock. MOST of my difficulty was the fact that I wanted to fit an oil pump which, hopefully, helps the flathead stay together longer.

You can check out a long thread pertaining to my oil pump shenanigans here:

https://www.chopcult.com/forum/showthread.php?t=55597&page=3

And, if you're interested, some videos of my oil pump experimentation:

https://www.youtube.com/watch?v=JCNS5lb-MzI

https://www.youtube.com/watch?v=u6ysWVEdj_8

In the right hands, and with a willingness to learn, I think a big flathead can be just as reliable as anything. I think big twin flattys ARE under lubricated compared to a 45. The 45s were TOUGH. As are their bigger cousins, the 74s and 80s. But like I say, I think for modern riding conditions at least, the big twins could really benefit from SOME type of upgrade in the oiling department.


There is still a lot left for me to learn, and I am now sorting out other issues with my BTSV. I need to pull the kicker cover and/or clutch pushrod on it now, because, the clutch will not stay adjusted no matter how many times I've fucked with it. But that's going to have to wait until after I finish replacing the trans output seal on my Panhead.

Also, I must acknowledge the fact that people like Jim who has posted in here, have helped alot me along the way. Chopcult, Pacific Mike, Matt @ Wheels Through Time, SS Cycle forum, hydra-glide.net, TatroMachine have all been a big help, whether they know it or not. I have spent a lot of hours reading and watching videos and otherwise consuming as much information as possible on the BTSVs, and the internet has been a big help.

A big shout out to the following people for all they help they've been to me on my travails with my BTSV (and my other bikes too!!!)

MontuckyMatt on various forums including this one (Matt)
Frankenstein on SS-cycle forum (Dick)
JBinNC here in this very thread (Jim)
Dragstews here on 33 (Jesse)
Cotten on SS-cycle forum (Cotten)



MontuckyMatt regularly rides his BTSV 70mph. He and I have very similar setups. I'm sure he will correct me where I might be wrong here. We both have 80" jugs with big ports and big valves relative to the stock configuration. We both run CV carbs. We both have upgraded oil pumps, he a 4 vane pump, me a gerotor pump. We both have "high compression" aluminum heads. (High compression for a flathead is still low compared to anything modern. The high compression aluminum heads are like 6.5:1 or something along those lines. I believe stock BTSV was 5:1 give or take). Matt is also putting some bigger cams in his at the moment I believe. 70+mph is possible on one of these BTSVs, especially with some of these mods^^^...... But for me at least, you run out of chassis and brakes LOOOONNGGG before you run out of motor. (Mechanical drums).

I was fortunate enough to visit the HD museum in Milwaukee not long ago. There are real pictures of an American GI shooting over his 45" flatty, both laid out on the ground. I also remember in the museum, a written letter from an American GI to the MoCo where the GI stated that a piece of the engine (not sure where) was smashed or shot off such that it was pouring oil out, yet the 45 laughingly carried him all the way back to friendly, Allied territory. So, the flatheads are TOUGH.

In summation, you should definitely get a big flathead. Or a 45. Or both.

Jim is right though, the parts support is probably a little less. You're close to one of the sources however since you're in Germany:

https://www.flatheadpoverty.com/our-dealers

[Rhysmort]

Out of all the BT's I owned my 74" BT Flatty was the best I've had.

I rode mine many 1000's of miles a year and I never even changed a pair of spark plugs in it. Now don't get me wrong, as Jim and the like have mentioned, there's not the network of parts and support like the 45's which are a huge market for flat track etc. But as a bike runs and rides? always fired up one or two kicks and was a really great machine. Simple as you like to work on as well.

Upgrades to the 4 vane in the oil pump and relief in the heads for bigger bang. A great machine!

[pete808]

I have had my 47UL for about 4 years now, it has been one of my best bikes when I am riding it. Most of the time it has been off the roads is due to me tinkering with it and not because it's acting up, although I have had a couple small issues. It is my favorite bike to ride out of all of my bikes.

[BuddhahoodVato]

Big Twin Flatheads have always been my favorite scoots. Once i dial them in, they start easy and ride for ever. Mind you, this scoot will not be extremely fast in stock configuration, but then speed was not my objective. Parts for them can be a challenge, but easily reproduced. I have had a few 45ci, not my cup of tea. but there is a ton pf parts for those suckers.

[CDeeZ]

I have had my 47UL for about 4 years now, it has been one of my best bikes when I am riding it. Most of the time it has been off the roads is due to me tinkering with it and not because it's acting up, although I have had a couple small issues. It is my favorite bike to ride out of all of my bikes.[ATTACH=CONFIG]108816[/ATTACH]

Damn good looking bike man. I'm always trying to find and connect with more UL riders out there.

[CDeeZ]

Big Twin Flatheads have always been my favorite scoots. Once i dial them in, they start easy and ride for ever. Mind you, this scoot will not be extremely fast in stock configuration, but then speed was not my objective. Parts for them can be a challenge, but easily reproduced. I have had a few 45ci, not my cup of tea. but there is a ton pf parts for those suckers.

Man, I'm glad to see some love for the old big twin flatheads. I felt pretty alone for a while with mine. Strength in numbers.

[montuckymatt]

Big twin flatties are super dependable. As long as you set them up right they will run a long time. Things like updated KR style combustion chambers and higher volume oil pumps make them mile munchers. I put 20 miles a day on mine with speeds over 65. I rode mine to sturgis a couple years ago. Did 600 miles in one day. Average speed was 65-70. Oh yeah, it was also over 90 degrees. Get a U model, you wont be sorry.

My 37U has hot cams, 4 vane oiling, cv carb, big intake valves, ported polished and relieved,electronic ignition, ULR heads and t&o wheels making it 84incher

[rockman96]

That is baddazz!

[CDeeZ]

Matt! How about a video with the new cams sounding off? Also, tell us more about your electronic ignition. That's something I'd like to do to mine.