Triumphrat

Mastiff-man · 02-26-2009, 08:51 PM

Is it worth it, an if not why?????????????????????

stewdog68 · 02-26-2009, 09:14 PM

yes and no

it's cost vs use of bike.
daily street cruiser i wouldn't worry to much but race bike or high rpm very often yes.

if you can get someone to balance your motor cheap than by all means do it. but $$$ is king

small motorcycle engine maybe/ $30,000 1/4/mile drag engine yes

My experience with Triumph motors is that a great deal of variation occurred in the factory, both in mismatched weights of parts and improper drilling of the flywheels. I have found crankshafts with not enough, and too much weight removed. I have found variation in the weights of rod sets of up to 15 grams from one motor to the next. Static balancing even a stock motor is a great improvement, resulting in less vibration and longer engine life by reducing out of balance conditions. This prolongs bearing life and reduces out of balance stress on all parts. Adding this extra step to all your motors, is going the extra mile to make your restorations better.

GrandPaulZ · 02-26-2009, 11:57 PM

stewdog has a reasonable answer, based on the subjectiveness of the question.

In any given situation, balancing is better than not balancing. HOW MUCH better is the question that needs to be answered, based on the intended use and available budget.

One thing about old Triumphs, and I'm not trying to take anything away from stewdog's post, there aren't a whole lot of them out there that haven't been messed with at one time or another since they left the factory.

Petty much anywhere you could go, and pick 10 similar triumphs out of a crowd of 100, you MIGHT find 3 or 4 that were nearly unmolested, and MAYBE one that is completely original. The nearly unmolested and/or original ones might have inconsistencies in construction, but they would be relatively insignificant to everyday operation.

GrandPaulZ · 02-26-2009, 11:59 PM

Hey, by the way stew, give me the number to that pro that balances engines cheap, I could use a reliable source!

TBS · 02-27-2009, 04:21 AM

I always have my engines dynamically balanced now. You have to give them the crank with sludge tube and plug, after any regrind, conrods with shell and small end bearings, pistons, rings, gudgeon pins and circlips. This is so worth while that I stripped my own engine that was built in 1994 and in my own concours '68 Bonneville as it felt so rough!!! By dynamically balancing you get rid of the "rocking couple" which is the sideways flex of the unbalanced crank that can't be removed by static balancing.

oldebonnie · 02-27-2009, 01:38 PM

Can anyone comment from experience on the relative benefits of static balancing versus dynamic balancing on twins with 360 degree cranks like Triumphs?

The only pro and con I have seen from an authoritative source is in Dwain Taylor's (Dusty's friend) "Tuning the 650 Triumph" booklet. Dwain saw little additional benefit from dynamic balancing over static balancing.

There is a guy selling a static balancing setup on eBay. Does anyone have any experience with this tool? He also sells engine stands and a couple of other tools that appear to be well-made.

Last, but not least, has anyone had a dynamic balancing job done lately? How much did it cost?

stewdog68 · 02-27-2009, 04:22 PM

every shop has different prices, but $150-300 dynamic, but have seen for as little as $50 on small (easy) engines.

Static no movement of part to balance
Dynamic moving,spinning taking all weight in ratio

best way to word this : everyone has changed a bicycle tire.

ok bike up side down, wheel facing up.

you grab rim and let go, watch the wheel it will slowly rotate the heavy end to the floor. ok with static method you just drill out a little metal and reset heavy end up top and see if it rolls again. repeat

Dynamic way: spin the wheel and computer measure all weight and factors and tells you where and how much to take out or add.
also take out side to side vibe. because part is moving

sorry this was the best way I thought everyone would under stand

GleaminTwin · 02-27-2009, 07:19 PM

When I had my motor rebuilt on my '70 Tiger I had the crank dynamically balanced. Cost was $300. The reciprocating masses that are attached to the crank (rods, bearings, pistons, gudgeon pins, piston rings) are weighed, then weights (equal to the recripocating masses weight) shaped like mini doughnuts are bolted to the crankshaft where the shell (rod) bearings would normally attach. Then the crank with the attached weights is spun at rpm's similar to the engine running on a special machine which determines what balancing adjustments are needed; and then small amounts of mass are drilled out of the crank's flywheel until it achieves dynamic balance at 85%. In other words, I think at 85% of max rpm, the machine dials in the crank to be very well dynamically balanced. I'm just saying my overall understanding of the process, so anybody who knows more about it correct me if anything I said is wrong. I think it's not possible to be perfectly balanced at all rpm's so it's normal to dial in at the 85% spot in the rpm range.

As far as differences between unbalanced and balanced, for me the difference is great. The vibrations at idle are less than before, and as the bike revs higher I believe the bike's motor is dramatically smoother than it was before. I think given the costs of a rebuild, it's money well spent to spend an extra $300. Also it will lessen the wear and tear on the motor's internals going forward. But the main benefit is the extra smoothness of the motor.

It might be one main reason I've been so careful breaking in my motor, because it basically revs effortlessly, and if I'm not paying attention I could easily be in the 5 to 6,000 rpms range. So, I'm always paying attention tryiung not to over rev it.

Now, on a side note, do you guys think that after I've logged 1500 miles on the rebuild I can cruise around at 5,500 rpms in 4th gear on the highway (probably about 90 mph with my 21 tooth sprocket) for say a 30 minute period and that'll be fine for the motor. Or is that over stressing it since it's a 1970, and therefore due to it's age a kind of delicate piece of machinery? What about doing the ton, is that reasonable on a '70 Tiger, or is about 90 topping it out? I'm just askin' 'cause this bike is my baby, and I don't want to push her too hard, but I bought her and fixed her up to ride her, not to just polish and wax her.

Picture of my bike:

Snakeoil · 02-27-2009, 09:36 PM

I'm basically a newbie here wrt Triumphs. But I've been around engines most of my life and work with very large rotating machinery for a living. All the side benefits of doing a dynamic balance are always well received. It's kinda like treating symptoms instead of root causes. I'm talking about smoothness to the rider as the most obvious with less damage to collateral components being a second order benefit. But the true value is the benefit to the bearings and journals. The out of balance condition is felt at the bearings and journals and that is the heart of any engine. Think of the crank as the hammer and the bearings as the anvil. Granted, vibes end up cracking sheet metal, braces, killing speedos and tachs, oil lines etc. but the real damage is to the bearings and journals. You might not see it right away, but you are shortening the life of any engine the more it runs in an out of balance condition. Now you can complicate things by adding in the natural frequency of rotating parts, but I don't think this discussion needs to go that far. Bottom line is if you are spending the money or sweat equity in rebuilding an engine, why not spend a few extra bucks to assure that your rebuild is going to last for a very long time? I see folks talking about spending money on higher capacity oil pumps, adding oil feeds to areas starved for oil, polishing connecting rods, etc.. All I can say is if you are willing to throw money at parts and mods like that, why are you reluctant to spend a few extra bucks make the moving parts move as smoothly and in harmony with the stationary parts as possible? You can put the most high tech oil pump in the world on an engine that is poorly balanced and the bearings will still fail. On the other hand, a well balanced and properly assembled machine will run quite well on a mediocre oil pump. Anyone remember the lectures about the value of establishing a good foundation? That's the value of a properly balanced engine.

oldebonnie · 02-28-2009, 12:12 AM

Snake, I don't question the value of balancing an engine. I agree with you completely on that point. I am asking if anyone has experience with both dynamic and static balancing and can compare the results. We have one source who says static balancing gave results that were very comparable to those obtained by dynamic after testing both methods in a number of engines. Static balancing doesn't adjust for side to side out of balance conditions (rocking couple) as TBS said above but that is not as serious an issue for these engines (360 degree parallel twin) as it is for some other designs.

If the results are truly comparable, the cost of a static balancing tool is less than a single dynamic balance job.