1973 TR5T intermittent engine knock

Hi Guys,
I have a very low mile 73 TR5T (~800 original miles) that has an intermittent engine noise I would like input on. I realize engine noises are nearly impossible to diagnose over the web, however I would appreciate input if anyone else has dealt with a similar situation.

For those who aren't familiar, the TR5T is the same basic unit 500 as Daytonas. This is my first Triumph 500, so I'm not accustomed to their normal noises.

The bike starts and runs very well and smoothly with typical Triumph valvetrain clatter.

After getting the bike up to temp on a ride, about a mile, I can hear a light knocking sound that ONLY occurs at 3,000 RPM. It doesn't matter what gear is selected.

I can't hear the noise under any other conditions. It seems to be equally loud on both sides of the bike.

It used a long screwdriver as a stethoscope with the bike on the side stand, but only hear the light noises from the valvetrain, no knocks whatsoever unless I'm riding at 3k rpm.

I've verified that the rotor nut is torqued and the primary chain is properly adjusted. Nothing seems to be loose and creating a rattle.

I'm hoping it isn't a bottom end issue, but will pull the bike apart if need be.

The bike was stored in a shed for 41 years on the side stand, that makes me wonder if all the oil could have drained away from the timing side main bearing, allowing corrosion to take hold over time, resulting in bearing damage.

Have any of you Triumph experts encountered anything similar?

Does it only occur on light throttle?

I do think it is most pronounced under light to moderate throttle. At least that's when I notice it most.

Fro http://www.triumphrat.net/classic-vintage-and-veteran/599826-t140d-engine-knock.html


1. Failed or failing timing side main bearing. (common - especially after improper winter storage - rumble sound - condensation collects in outer ball track leading to rusting - often seems to be coming from the back of the primary cover - more of a rumble than knock)
2. Failed or failing rod bearings. (not so common - deep knock - varies with load - do not ride the motorcycle)
3. Failed or failing drive side main bearing. (very loud rumble - definitely sounds like it is coming from that area)
4. Drive side main with too much diametric clearance. (knock - Most noticeable when rolling off throttle while engine under load - especially at the top of a grade - load related)
5. Failed wrist pin end of connecting rod. (knock - again load related)
6. Rotor body loose on center. (knock - common - rotor needs to be replaced)
7. Loose rotor nut. (knock - common - should be Loctited with blue AFTER proper cleaning of the threads)
8. Clutch hub rubbers failed.
9. Piston slap (common with 750 twin - goes away as engine warms up)
10 Chain loose (more of a tapping sound - common)

My guess = #6 on previous list.

Sure it's not 'pinking' or 'knocking' due to poor fuel or similar?

The Valvetrain should RUSSTLE , not clatter . Half assed dick wits who cant set tappets accurately , or cant be bothered ,
or trenching on vale stem tips can get it awkward . But SET EM RIGHT and they shouldnt like a can of marbles .
the distinxctive triumph timing gear whine should be there , if you listen for it .

Yea , G.P. is likely right . A shiity rotor , will have swarf from loose center maybe . Welded Centers have W stamp .
Common Fault of alty nator .

If its the bearings a gentle ? rise will get it on Max Tourque at low revs , either a grumble ( bearings ) or KNOCK ( con rod ) .

You should have no trouble pretending to be Steve McQueen on that . A turkey had a speedmaster Fr. & Yoko 4.70 knobbly R .
on one to tryn scrape the pegs . Rcons he did occasionally but was likely the falling off , fairly occasionally that scraped em .

Following up on this old post, I now have the TR5T fixed.

After checking all of the "easy" things, I decided the engine needed to come out.

I tore the engine and gearbox completely down for inspection. All components looked to be in excellent condition and showing virtually no wear, as would be expected for such a low mileage bike.

The timing side main bearing had just the slightest little bit of audible noise when spun gently by hand, so I decided to cut it open to determine if it was the culprit. After sectioning the bearing and examining under magnification, I could see several very faint pits on the outer race in the center of the ball track. The spacing of the pits matches the ball spacing, so they are most likely corrosion pits caused by a stationary crankshaft during long term storage.

I work with bearings daily in my day job and am really surprised that such tiny pits could cause the knock, but definitely believe that the damage would progress rapidly at this point and failure would follow quickly.

I replaced both main bearings for good measure and reassembled the engine. The bike is now back up and running well, even better than before. Could also just be my imagination, but it seems to have less vibration now. I suppose the pitted bearing could have imparted some added vibration as the balls passed over the pits in unison.

Took it for a nice long test ride this week to take advantage of the rare 55°F December day. The bike ran beautifully, but must have picked up a nail in the rear tire as I got back to town. Had to call for a trailer and ride home... :lol:

Glad to hear about that.

love the bike, been wanting one for years, very very nice. I have a similar problem on my t100t. and have been coming to the same conclusion, as the bike was left standing for years. this will have to wait until other stuff is finished. really glad you got yours sorted.