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The 100 Forum

BN1 engine vibration

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davewood Dave Wood
Saanich, BC, Canada   CAN
I recently purchased a well-restored BN1 but it has a lot of annoying vibration – especially around 2000 – 2200 rpm.

The manual implies that one cause might be:
• Loose dynamo bolts
• Fan blades out of balance
• Incorrect clearance for engine front mounting rubbers
• exhaust pipe mountings too tight.
• incorrect adjustment of stabilizer

When I blip the throttle, the engine doesn’t “rock” even a millimeter – so that seemed like a good place to have a look. There is a very robust mounting bracket attaching the exhaust pipe just below the manifold to the engine block. This is bracket allows for no movement whatsoever.

Should I loosen it so it “slops around” within the bracket and therefore allow some isolation from the engine?

I’m not sure how to interpret “Incorrect clearance for engine front mounting rubbers” or “incorrect adjustment of stabilizer” – i.e. what to look for or how to correct it.

Any help is much appreciated.

Dave Wood

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Luegolover Avatar
Luegolover Steve L
London, London, UK   GBR
Hi Dave,

I think that bracket is the original and therefore correct bracket to support the exhaust. I suspect it isn't the cause.

I don't have anything optimistic to add though.

Good luck
Steve

davewood Dave Wood
Saanich, BC, Canada   CAN
Hi Steve,

Thanks - I think it is original as well but I can't fathom why it would be like that since if clamps it to engine ... ahh. I had been thinking of it as clamped to the frame, but it is to the engine block - so it shoud be able to rock on the motor mounts. The rubber mounts are all new and look correctly installed. I'll keep looking.

Cheers, Dave

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Koudekerke, Zeeland, Netherlands   NLD
Hi Dave,

Check the engine mounting rubbers, they do need a gap of 1/22 Inch (0,8 mm), between the horizontal and vertical mounting rubber.
See the drawing.


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BobAH100 Bob Markovich
Patterson, NY, USA   USA
Suspect the wide fan belt used on 100s, which also compromises the crankshaft by vibrating; replace it with narrow belt and pulleys.

Vibration is especially bad for this long stroke engine, which suffers from torsional vibration anyway—really bad for the crank. Also suggest a lighter flywheel (25 lbs or so) and a front vibration damper, available from Denis Welch and AH Spares.

cpcooper Craig Cooper
Chico, CA, USA   USA
I’ve been chasing vibrations in my BN1 for about 30 years and have come to the conclusion these motors vibrate. Not to say nothing can be done, but I’d advise checking some other 100’s to see how they compare to yours. I suggest taking the fan belt off and running the motor briefly to see if there’s a difference. I went as far as disconnecting my front mounts, supporting the engine with a floor jack and running it. Make sure your entire exhaust system is isolated from the body/frame with rubber mounts. One area I got MORE vibration from was replacing my badly deteriorated transmission mounts with nice new firm ones. Good to check there though too, and confirm gearbox/OD is isolated from the frame. My vibrations were still unacceptable confirming all the above and I ended up going back into the motor, replacing connecting rods, and having rotating mass balanced. Still not like a Toyota, but I can live with it.

The narrow fan belt helps, as does adding a harmonic balancer to the front. The balancer from a 6 cylinder motor will work, and also takes care of the narrow belt pulley on the crank, so you’ll just need water pump and generator pulleys. DW sells both, but the generator pulley is pretty easy to find from a Lucas generator for just about any Brit car but a Healey 100. Note here there are people who will tell you the harmonic balancer should be engineered specifically for the characteristics of the 4 cylinder motor, but DW and I believe AH Spares show the same part numbers for balancer for 4 and 6 cylinder motors. You will notice slightly slower revving when you blip the throttle.

davewood Dave Wood
Saanich, BC, Canada   CAN
Hi to all,

Thanks - all good ideas from experienced users - who have "been there." By the way, the manual implicates the "stabilizer" as a possible source. Does anyone have an opinion on that focus?

I've very heartened by the generous response of strangers to my problems.

When I do find an answer, I'll post it for all to see.

Cheers, Dave

cpcooper Craig Cooper
Chico, CA, USA   USA
Ah yes, the stabilizer. Yet another place to check to assure your engine, trans, OD are all isolated from the body/frame. When I first put my BN1 together, the loop on the bottom of the OD adapter was missing, so I had no stabilizer. Eventually, I bought a replacement adapter on eBay and installed it which enabled me to install the stabilizer. No real improvement, maybe a little worse vibration. Probably best to disconnect one thing at a time; fan belt, stabilizer, motor mounts, exhaust bracket... and see if you can isolate a problem. In my case, I had just about everything unhooked, with the motor supported by a floorjack, and it was still doing a pretty good rendition of the Hokey Pokey. Things got a lot better with balancing and adding the damper to the front, but I still fantasize about designing an external counter-vibration device, kind of a caveman version of the balance shaft Mitsubishi developed that made their long stroke 4 cylinder engines run like silk.

davewood Dave Wood
Saanich, BC, Canada   CAN
Hi Craig,

Thanks for another update. I didn't realize I'd be learning so much so quickly about parts of a car I didn't know existed!

I thought I should clarify something. The annoying thing about the vibration is that it is transmitted so much into the frame and body of the car. The whole cowl "buzzes" - and the fact that the engine doesn't "rock" in the slightest when I blip the throttle.

I'm used to seeing a considerable lateral movement on "blipping" the throttle so that was my first impulse - to see why the rubber mounts were not allowing for some movement. So I'm hopeful that the clearance between the bracket and the rubber stopper may add some relief. I'm not sure that small clearance would be significant but hopefully ...

Cheers, Dave

cpcooper Craig Cooper
Chico, CA, USA   USA
Hey Dave, you raise a good point; the other side of this is going after what's making the buzzing. Vibration is a lot more tolerable if you get rid of the buzzes. Check out this horn, imagine the noise it must have made as it vibrated against something, probably for years. I had an awful buzz in my dash for years, until I realized I was missing the little bracket that braces it to where the mirror mounts above. (screw in dash next to OD switch. I also had some buzzes with the grill and the pieces behind it that direct air to the radiator. I read recently about people using different adhesives when installing the front shroud, so that it can't buzz against the inner structure. Maybe have someone run the engine at "buzz RPM" while you search around for what's making the noise? I don't think these motors rock a lot when blipping the throttle, but if you want to send me an email or PM with your phone number, I'd be happy to make a short video of mine and send it to you.

Good luck to you. It's very satisfying when you finally get it!

Craig


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davewood Dave Wood
Saanich, BC, Canada   CAN
Hi Craig,

I'd appreciate a video very much. My email is dave.wood@typefocus.com

Cheers, Dave

hamgr Avatar
hamgr Graham Hammond
Littlehampton, SA, Australia   AUS
Hi Dave
Some Healeys suffer from whats called scuttle shake, from what i have read sounds a bit like what your experiencing.
Lots of possibilities from old tires, wheel balancing, brake drum balancing. Maybe worth investigating. Search scuttle shake Austin Healey on the internet for more information.

Cheers Graham

Michael Oritt Avatar
LUSBY, MD, USA   USA
Dave--

Congratulations on your acquisition.

You do not say whether you have owned any LBC's before and while issues of vibrations and noises certainly vary from car to car certainly if one is used to driving any late mode car in reasonably sound condition a Healey--even a well-restored one--may seem like a collection of loosely connected car parts. And regardless of your car ownership experience bvefore making serious changes, etc. some seat time in another 100 might provide a good point of reference.



Best--Michael Oritt
1954 Austin-Healey 100 (street)
1958 Elva Courier (track) FOR SALE
1959 Elva MK IV sports racer (track)
1961 Ginetta G4 (track)

BobAH100 Bob Markovich
Patterson, NY, USA   USA
Agree with everything except scuttle shake, which emerged only with the heavier sixes (as did frame cracks around the engine mounts, which you really don’t see on the Fours, as even these engines are far lighter than the Healey six).

But as the vibration is at rpms, rather than road speeds, I suspect it’s engine related. Narrow drive belt and pulleys and a front mounted vibration damper are relatively cheap and easy to add—and may delay crankshaft failure, an issue with the long stroke Four and its inherent crank flexing.

Pricier but also critical is a much lighter flywheel, from D Welch or AH Spares.

A final thought: the motor mount buffers may simply be so hard that they are transferring more vibration to the chassis, setting up a resonance at a certain RPM. No big deal by itself, but protecting the crank with what I have recommended—and done on my 100–is still vital.

davewood Dave Wood
Saanich, BC, Canada   CAN
Hi - thanks for all the good ideas.

I took a video and posted it on youtube:

It is a 10 seconds and just shows me blipping the throttle and you can see there is no noticeable engine rocking. Is this what others have experienced?

Cheers, Dave

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