crabmaster
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Posts: 44
Attribute: http://www.austineighteenhundred.com.au
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Post by crabmaster on Nov 21, 2013 10:24:55 GMT
I've always been a bit dissatisfied with the amount of vibration felt through the car coming from the engine. So, I decided to try and find out the cause. This was quite a long investigation but one aspect will be of interest to readers since it is not something ordinarily considered. As we all know, the front crankshaft pulley serves two purposes. One is to drive the fan belt, and the other is to provide dampening of torsional deflections of the crankshaft as different pistons apply their power stroke. The harmonic damper is the outer pulley which is bonded to an inner lighter disc by a rubber strip. Often the rubber deteriorates from oil leaking from the front seal and in severe cases, the pulley can come right off the inner part if the rubber just disintegrates. Since I was looking at everything to do with vibrations (such as engine mounts - of which more later) and so on, I thought I would have a good look at this pulley, or harmonic balancer, as it is often called.
My particular car had stood for some 30 years in a dry garage and so everything had dried and become brittle - inlcuding the rubber ring in the harmonic balancer. It had the consistency of petrified bone. Application of a screwdriver merely broke off small pieces. "Not much vibration absorption happening here" I thought. Feeling that there should be some give in the rubber, I scouted around various places to find a new pulley. A local MG restoration outfit had one. I went over there with my old pulley and a screwdriver to examine it. The sales person put the new (really second hand, but nicely cleaned up) pulley on the counter, and I put my old one next to it. I deomnstrated the problem with the old one with the screw driver, and asked permission to test the new one to see if the rubber was soft. He refused, saying it would damage it. So, we both stood there staring at both pulleys, with me trying to decide to part with folding money because the new one looked better than the old one. There was a pen on the counter. So, I asked if I could just touch the rubber on the new pulley with the tip of his pen. I think he must have realised how ridiculous the situation was and permission was kindly granted. Thankfully, the rubber of the new pulley deformed very nicely upon application of the pen, and so it was purchased and refitted.
I am glad to say that this made a substantial difference to the vibration from the engine. It did not cure the vibration problem completely, but enough to notice inside the car.
Something to check next time you have the pulley off.
Tony
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Post by dave1800 on Nov 21, 2013 12:03:58 GMT
Very interesting analysis Tony. I wonder how many even consider this as an item to examine even though it may affect engine life? One thought, mainly for Tommy's benefit - (you will see he loves timing and camshafts) is whether the timing marking is identical to the one on the pulley you took off? If not what method did you use for establishing TDC? I believe these pulleys can fail when the rubber goes soft with oil and the inner and outer parts can rotate such that the timing mark is no longer accurate. In your case I guess that was probably not the case with the dried out hardened rubber.
Regards
David
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crabmaster
Member
Posts: 44
Attribute: http://www.austineighteenhundred.com.au
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Post by crabmaster on Nov 21, 2013 19:24:30 GMT
Interestingly the MGB (chrome bumper) has the same pulley as the 1800 - Part No 12H963. The later MGB has part number 12H3515 which is the same dimensions, but with the timing mark in another place so that it can be read from the top rather than the bottom. But, I suppose there's nothing to stop one putting a mark in the former position. If so, then lining up the keyways on both pulleys and scribing a mark is probably the best way to locate the correct position of the mark.
When I first looked at the old pulley, I thought it was in good condition - until I touched it.
Tony
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Post by Penguin45 on Nov 21, 2013 19:32:35 GMT
Interesting. One of my former work vans was an LDV 300, which had the Landrover 2.5l diesel engine in it. The pulley parts sheared to an extent such that the charging light would come on occasionally. Finished up drilling into the gap at eight places, threading the holes to M8 and running set screws down. I got another 18 months out of that!
Chris.
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Post by dave1800 on Nov 22, 2013 2:37:22 GMT
The later 1800s had the timing mark and pointers repositioned so you didn't need to crawl under the car. Possibly because of the wider availability of moderately priced brighter xenon strobe lamps instead of those cheap neons? Maybe the later 1800 pulleys are the same as the later MGBs too? regards David Interestingly the MGB (chrome bumper) has the same pulley as the 1800 - Part No 12H963. The later MGB has part number 12H3515 which is the same dimensions, but with the timing mark in another place so that it can be read from the top rather than the bottom. But, I suppose there's nothing to stop one putting a mark in the former position. If so, then lining up the keyways on both pulleys and scribing a mark is probably the best way to locate the correct position of the mark. When I first looked at the old pulley, I thought it was in good condition - until I touched it. Tony |
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