1972-75 engine, big bore 88mm?

A buddy just bought a shed load of Husqvarna parts. Among it is a '72-75 engine with 10 cylinder fins so either a 400 or 450 we reckoned, but the bore is 87-88mm and stroke circa 84 mm. That should make it around, or slightly over, 500 cc. Stock bore would be 83,92 mm stock according to huskyclub.com

Anybody heard of big bore tuning to these engines? I haven't been able to find out what stroke is in a stock 72-75 engine either, anyone here know?

Grateful for any info!

(Photo is not of the engine mentioned, only to show what engine type)

400 CR (MK Frame):

Bore - 81.50
Stroke - 76.00


450 / 460 CR (MK Frame):

Bore - 84.00
Stroke - 82.00

The distance between the head and barrel in the photo tells me its a 400. My 73 400 450 Owners Manual shows that the largest piston for the 400 is an 82.50, thats not to say a larger aftermarket wasn't available at sometime however I don't think the 400 cylinder would allow an 87mm bore without being dangerously thin at the bottom.

The 450 cylinder also has 10 fins so based on the fin count a 400 and 450 could look the same. The key to identifying a 400 is the distance between the head and barrel, if you can put your thumb between the two its a 400 if not its a 450. Since the above photo isn't the motor you're referring to I think you may have a modified 450.

Any chance of getting an actual photo?

Heres a pic of a 73 450. Notice the narrow head to barrel gap and the distance the barrel is from the clutch cover.

Thanks guys for all the good info! Will get some pics of the actual engine soon. Pretty sure the head/cyl-gap suggests it's a 450 then.

I'd sure love to see the piston, and the crank. Wonder if these components are from a preexisting bike that where modified or if they were machined from a billet.

If the engine is still in the frame - another quick way to differentiate a 400 from a 450 are the front mounts - the 400 is curved toward the engine while the 450 is angular. The spacing on the mounting holes are also different.

Engine is not in a frame and I don't think there is a frame for it in the pile.. Lots of other loose bits though, so thanks for the tips.
Great to get the info so we might be able to identify some of the stuff. Photos will follow of exterior at least. Hopefully some of the internals too soon!

Looking forward to it!

Stroke is 82 mm so that is stock according to Vinskords numbers. Also the front mounting hole measures were helpful and 135 mm so a 450 engine.
Bore is 88 mm. Only markings on the piston says 07/0, and the arrow pointing forwards (see pic). Any clues?

The pictures look great - thanks for posting. Any chance you have a side picture of the piston?

Yes, of course! I forgot those pics.

A picture of a standard size OEM piston. Does yours have any of these markings underneath? (A small dental mirror helps to see sometimes.)

I have no idea what the 07/0 means. The piston looks like a Husky mahle but 88mm is larger than anything I have ever heard of. The sleeve is certainly thinner than the super thick stock 84mm. Makes me wonder if that thick sleeve was possibly a plan to lead into a 500 motor in the 70's.

I'd sure like to know where that 88mm piston came from. Wondering if its from another make of motorcycle engine or if Husky had Mahle mfg a few of them to test out the 500 concept.

As starved for air as the 450 is I doubt an 88mm bore added a whole heck of a lot in the way of performance.

I see the 5 spd counter shaft has been upgraded to the spline shaft or it has a six spd trans.

In any event I think its a cool find. Thanks for posting.

Thanks for the good info. I'll see if we can get some pics up the skirt of that piston!

Here goes! Markings under the 88mm piston. Same as the markings on the standard piston you posted Vinskord, but with some additions.

MAHLE 138
84P12 and a 9 (maybe)



Looking close at the upsidedown stamp between MAHLE and 138 it says 1/14/3

Still a mystery - Maico 501 Mahle pistons are std. 91.52 mm and the largest HVA 500 CR piston is 86.92 mm.

May want to carefully scrape or wet/dry sand the remaining carbon off the top of the piston to see if any other numbers are hiding underneath.

Any out of the ordinary numbers stamped in the cases - on top of the cases under the carb, underside by the front engine mount, or right below the cylinder either right or left sides?

Crash's theory seems the most probable at the moment.

Tempting to throw in a rolling frame and see how this oversquare configuration rides!

If you make this happen be sure and report your findings.

At first look we haven't seen any odd no's stamped on it, but will look closer. Same with piston top.
The owner has a (semi-)rolling frame for a '73 360 R/T that he plans to put the engine in. It may take
some time before it gets done but I'll report back then. Thanks!