TR2/3/3A How much vibration in a Triumph 4 cylinder engine?

[TuffTR250]

My TR3A has a TR4A engine, per the block and head numbers. I recently rebuilt it with very many new parts including pistons, valves, cam, timing gears and chain, all new motor mounts, etc. etc. I had the main rotating parts balanced by an experienced machinist including pistons, each end of the rods, crankshaft, flywheel, and clutch pressure plate. The machinist punch marked the crank flange, the flywheel, and the clutch pressure plate and told me it should be reassembled just exactly as he balanced it. So I double verified that I had everything lined up to his punch marks. My problem is that I was expecting it to run with almost no vibration. However, when I put my hand on the front of the cowl and the fenders I feel quite a lot of vibration. Also when I put my hand on the bottom of the oil pan I feel quite a lot of vibration. And if I put my hand on the side of the valve cover I can feel quite a lot of vibration. Another test I was told about is to put a flat bowl of water on the hood (bonnet) and the movement should create a nice concentric set of circles in the water if it's running good with not much vibration. But what I'm getting is a just a big movement of the water and no circles. I have not tried this water test on my TR250 but I do not feel nearly the vibration on my TR250, of course it is a 6 cylinder. Is it normal to have quite a bit of vibration in the 4 cylinder Triumph engines even after having them balanced? Thanks!
Regards,
Bob

 

[TR3driver]

A BIG 4 cylinder engine (without a balance shaft) is never going to run perfectly smoothly, or even as smooth as your TR250. Might be worth double-checking the motor mounts, but what you describe sounds fairly normal to me. (Except the water test, never heard of that one.)

In fact, it's fairly common problem on TR3/A for the vibration at idle to bounce the hood up and down enough that the latch mechanism squeaks and/or the hinges rattle.

PS, there is a discussion of part of the inline 4 cylinder vibration problem at https://www.autozine.org/technical_school/engine/smooth2.htm The "Continue" page presents the reason that inline 6 cylinder engines have much less vibration.

 

[dgaldrich]

And make sure you're firing on all 4. A problem with one of the plugs, plug wires or cap could cause a weak spark and the same symptoms. A small vacuum leak can also cause a little roughness at low speeds. As others have said, it's NEVER going to let you balance a shilling on the rocker cover but it really should be smoother than you describe.

Dave

 

[CJD]

Yep, inline 4 cylinders have second order vibrations that cannot be balanced out. High end inline 4's have an extra balance shaft to eliminate the second order, but not our simple engines. Don't worry, it is still important to have everything balanced, as it removes much of the bearing stress...so you did good.

 

[charleyf]

Bob,
there is no mention of the engine speed, except at idle. A low idle of 600 is going to give a lot more vibration than an idle of around 1000. Also another possible area for some vibrations is the fan itself.
I have two TR4's the idle on one is very smooth while the other is rough until it gets up to 1000 or slightly above. Which makes me keep the idle speed up on the second car.
Charley

 

[sp53]

My experience has been that proper ignition timing and fuel mixture make a big difference in vibration also. Try moving the knurled nut on the distributor up and down to find a sweet spot and at the same time play with the idle some, plus keep an eye on the spark plugs for deposits. If the plugs start building up with deposits, the idle will be rough and of course make sure the valve timing is loose enough. Moreover, the old saying what is wrong with my SU carbs is my Lucas ignition. I have found that a good distributor that advances and falls back correctly makes a big difference in idle speed and engine smoothness.

 

[TuffTR250]

I have it idling at 1100 rpm. It seems to vibrate most at around 1200. I have not tried to lower the idle speed as I prefer it to be idling a little faster than the book calls for. It sounds to be running really pretty good when I listen to the exhaust sounds, as the manuals recommend. I have worked on the fuel mixture a lot and have balanced the air flow between the carbs. I've got rebuilt distributor with Pertronix, new TRF fuel pump, new Kobalt wires from Moss, and the spark plugs are fairly new. I had oversized throttle shafts put in the carbs and while apart I cleaned the carbs up with BrakeKleen and put some new cupped washers in the carbs. However, they still have the same needles and jet bearing as when I got the car. So I keep wondering if getting the carbs thoroughly rebuilt would help it run with less vibration. What are thoughts on that?
Regards,
Bob

 

[TomMull]

A "normal" or "acceptable" amount of vibration is difficult to define. Might be good to compare yours with others in the area. A balanced engine will not necessarily be smoother at idle but rather at speed, in my experience. Tom

 

[TuffTR250]

Randall, that was a very interesting article on engine vibration. I guess I kinda suspected the differences in the 4 cylinder and 6 cylinder engines, but I've never read an article that explained it that clearly and in that detail.
BTW, I called the machinist this morning that ground the journals on my crankshaft and he said that when they grind the journals that ensures that the crank is straight and should have no runout. Thus I'll rule out any problems with crank runout.
Tom, good idea, I'll check on other 4 cylinder Triumphs in the area. I've never really thought to check specifically for vibration on other Triumphs at local shows, etc.
Regards,
Bob

 

[glemon]

Although describing or perceiving vibration is very subjective, it sounds to me like you are getting more than you should. Even though you just had the engine rebuilt, I would guess the issue lies with timing and/or mixture, and in any event these are much easier to adjust or fix than engine internals. My guess is timing is off, I would just slacken the nut on the distributor and slowly turn the distributor back and forth (with a leather glove on) while the car is running and see if it smooths out. Some people prefer to be more scientific than that, but it will tell you quickly if you have a timing problem, and you can mark where you started as a reference.

My old TR4A engine was a sweet runner after I rebuilt it, with a nice even idle and a real nice power curve from about 2000-4000 rpm (stock except for 87mm pistons and high compression). It didn't ever run like a new Lexus, and never will, but I would not describe the motor as rough, excessively vibration prone (this is compared to similar era British sports cars, not modern iron).

 

[TR3driver]

I had oversized throttle shafts put in the carbs and while apart I cleaned the carbs up with BrakeKleen and put some new cupped washers in the carbs. However, they still have the same needles and jet bearing as when I got the car. So I keep wondering if getting the carbs thoroughly rebuilt would help it run with less vibration. What are thoughts on that?

Well, the needle and jet can wear (if the jet wasn't accurately centered or there is excess play in the dome), which can lead to some strange mixture problems. But, since you set the mixture at idle and that is where you are having the problem, it seems really unlikely to me that it is from worn needle or jet. In other words, when you adjust the mixture, it would compensate for any wear at idle. The mixture problems would show up at higher flow rates.

Also, I've never noticed any particular relationship between mixture and idle vibration, until the engine starts misfiring of course.

 

[sp53]

I have never had the electronic ignition on my cars, so the way I do things might not fit in. For me a 1200 to 1100 idle is too fast and would hide some of the precision of the tune up by advancing the timing and allowing too much air. I like to get the engine down around 900 for the final settings that are done more by feel than numbers. Like stated engine vibration from a couple of thousand miles away is subjective and I have never owned a triumph 6 cylinder, so I would not know that comparison. I would suggest running the engine at 900 the best you can and have a look at the plugs and the timing, but again I do not know just what an electronic ignition does on a Triumph, and on my Saabs the timing cannot be moved. I once saw a new rebuilt tr3 engine run rough because the oil rings did not seat, so you might see if the plugs oil fowl some.

 

[TuffTR250]

I've tweaked the timing with the vernier. I prefer using the vernier to adjust the timing since that makes it easier to tell how much the distributor has moved and where I started. Right now I have the timing set at what I've estimated is 3 to 4 degrees BTDC, but it is difficult to know exactly since there is no degree marks to go by. I'll give it a try in reducing the idle speed to around 900 rpm first, and then tweaking the timing with the vernier, and then by turning the distributor, to see if any of those actions reduce the vibration. Thanks for the recommendations!!
Regards,
Bob