Bonneville America Forums Forums Technical Forums Performance Mods Big bore reliability

I was wondering how many miles you big bore guys have put on your engines after the mod. . It's fairly well documented that you can get 100,000 miles plus out of the engine in stock form. I have been contemplating doing the big bore kit but I don't want to shorten the engines life span or it's reliability. In my experience with muscle cars and Harleys, it seems when you bore out the engine etc. the reliability goes way down.

I have put 10K or so on my bike since the 904 was installed. I haven't had a lick of trouble from her. I switched to Nology coils and wires as well as iridium plugs and pod filters at the same time as the BB. She's even stronger now that she good and broken in. Gas milage is great; I got 45mpg on a 500 mile trip this past weekend, and that is with the 16 tooth sprocket. Get the Big Bore- you won't regret it.

I can really only speak for the 904 though. The bigger stroker kits might be a different story....

I trust my motor even more with the 904 than I did with the stock motor. I bought mine with 3400 miles and it burned oil and leaked at the head gasket. I installed the 904 at about 11000 miles, now have over 27000 of problem free riding. No leaks, no burning oil. Much power. And I'm the kind of guy that hits the rev limiter all the time and will do the ton almost every time I take the bike out.

I put about 36k on mine with the 904, 62k total miles to date.. I just pulled it apart and the pistons, cylinders and bottom end all look great. I have never been nice to it either! The head is another story. It wore out the cam bearing area. I don't think the big bore had anything to do with that.
If you ride it like a normal man should, i think it would easily go as far as a stocker.

more than 10K miles on the 904 no issues, runs stronger than ever. been on several 500 mile plus per day rides, uses no oil and gets low 40s mpg.

I doubt the 904 kit would effect longevity, it isn't radical compression and really isn't much bigger displacement than later model BAs or SMs. I used to bore out the old bikes about 20 to 30 over all the time and run Wiseco forged racing pistons with 10.5:1 compression. It never effected engine life. I would run a few top ends to 1 bottom end on those every time.

Big bore is well worth the price of going from 790 to 904. The 865 to 900...why??? Cams from 02/03 do the trick to 865s.
With that said, My Speedmaster only has about 38k miles on it, 25k with the BB, no problems whatsoever.

Biggest difference is that some swear by the nickaseal (sp?) coating inside the jugs. Wiseco BBs have steel sleeves which should run about 50k miles, then check them out. As stated above, they could still look and run cherry, just needs a brush-up with the honers anytime you take the pistons out. New rings as well.
The nickaseal cylinders, as offered form an LA firm, (Matt Capri's lot) as well as the FL Triumph speed shops (Bonnevilleperformance and D&D) I may be mistaken about who does what, but the nickaseal sleeves "CAN" last longer then the steel. They are stronger and can take the persistent friction better than just bare steel with chrome rings, therefore not wearing the sleeves or piston rings out as soon.
The physics behind them is sound, plenty of room for the Triumph to add the power. Tranny, rear end, brakes etc can easily handle the extra torque and ponies. (Watch clutch springs though)

The part about the cam holders is also very accurate. The aluminum head parts will wear-out far before the big steel stuff will. But...if you used bearings on the cams, you would need really heavy duty ones. That my friends is why these bikes are under the magical $10k mark. You could improve a lot of these bikes, just gonna cost ya. Transparent aluminum?

Speed is $$
How fast ya wanna go?


Stroker??? Hmmmmmm may be this winter's project.
.

That may be true for a car since in most cases by the time the head wears out on a car the body is shot too and few want to go through the trouble of totally rebuilding one of todays disposable cars. Now where a Triumph in concerned most people I know would rebuild and rebuild and rebuild not dispose of like a Jap bike or car. The lack of bearings makes that much more expensive to do. I don't even remember how many times I rebuilt my 66 TR6C anymore.

I have about 15K miles on my 904 (no sleeves, bored and nickasil coated just like a stock engine). I've measured the compression and both cylinders were right at 175 which doesn't seem more than stock.

Bike couldn't be running much better and I'm very confident in the bike. Whatever problem I may have, I doubt it will be related to the BB.