Technical vibration / balance
- Thread starter Mike r
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Technical vibration / balance
I have a 650 engine fitted and it required a spacer as the exhaust was hitting the rear cross member and the flywheel was very close to the engine mount. I tried both the stronger spring, which I already had and used when I had the 500 engine fitted and the original spring.
To be honest neither spring had any really noticeable difference on how much the engine moved about when it was running, so I don’t think the uprated spring is the cure.
In the end with the 650 I used the original less strong spring as the stronger one still made the engine sit too high and the exhaust was still banging on the rear cross member. The spacer is 18mm.
Tony
To be honest neither spring had any really noticeable difference on how much the engine moved about when it was running, so I don’t think the uprated spring is the cure.
In the end with the 650 I used the original less strong spring as the stronger one still made the engine sit too high and the exhaust was still banging on the rear cross member. The spacer is 18mm.
Tony
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That's handy to note for future.
Not sure what else I can add other than anecdotally my 500 and 126's in the past have never suffered from issues relating to the engine mount spring. It's not something I've ever had to think about.
Michael
the hobbler
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I run a 'well tweaked' 126 engine in the back of my 500, sitting on a standard 500 rear mount. Although it has a 'hotter' cam (35/75/75/35), I have retained the standard push-rods and cam-followers (new, as one always should do with a new cam) and have not suffered vibration problems---to the point that when I had my Dellorto FZD set up on the local 'Dyno', the operator pointed out how smooth he thought the engine was, even at 5,200rpm. So, the answer to your query is this---the retention of standard cam-followers and push-rods should NOT be a contributory factor with regard to your engine vibration.
Reading all the various comments,it would seem that a possible cause is that the engine is not sitting 'free'---have you checked the 2 gear-box mounts? If they are broken, the gearbox will sit on the cross-member, and therefore transmit vibration through the car.
Reading all the various comments,it would seem that a possible cause is that the engine is not sitting 'free'---have you checked the 2 gear-box mounts? If they are broken, the gearbox will sit on the cross-member, and therefore transmit vibration through the car.
Hi Mike, I have to agree with Tom@the hobbler , I have the same cam, it should not cause your problem. I also have the Panda head but have changed the original carb mount for a low level item. Just a thought have you done the following -
stand at the back of the car and grab the engine firmly then push and pull HARD from left to right
note any knocking or scraping noises from the bodywork - OR - start the engine with a spare body in the seat and get them to rev the engine, at the same time check for engine movement and for vibration through the bodywork if you don't get any indications then it's only happening when in motion. If this is the case then the engine must be moving when the wheels are being driven so check that the gearbox is not contacting the underside of the car and transmitting the vibration let us know what you find.Ian.
Michael, seeing that you have changed so many possible suspect components,since the start of this, maybe you could check the ones that remain? The impeller would be on my list; it wouldn't take much distortion or imbalance to really mess up the running of the engine. I've run a few engines completely free of the car and if anything, they're less bouncy as the revs go up.
Yes. Everyone here swears by the alloy ones. Despite me admittedly being ignorant of their qualities, when you look at the fine construction of the standard fan/impeller and consider the rpm. it goes at, not much imbalance would be needed to create catastrophic vibration; same thing if it was loose or possibly with worn bearings on the generator. I guess you've tried the engine briefly without the belt fitted?
Worth a try.....
Hi Mike, If you skim the head you change (lower) the effective distance that the pushrod has to operate over and thus the effective angle the rocker arm operates over. Depending on the cam fitted and the lift given at the valve (max cam lift x 1.5 = max valve lift or opening.) To obtain the maximum effective lift at the valve the rocker arm should be parallel at half cam lift. So to obtain this my pushrods have been shortened by approx 10mm each. (note this figure will be dependant on the amount of material removed from the head) The problem my mechanic found was that with standard valve guides the given lift was enough to bring the underside of the valve spring retaining cap into contact with the top of the valve guide so the guides were adjusted to suit. This was with standard valve spring sets not anything modified. If your engine has been modified with a differing cam and the max cam lift is approx 7.25mm x 1.5 = 10.875mm at the valve. (35/75-75/35 cam) there is a possible chance that contact is being made. If your cam is wilder than this the possibility becomes greater, but it is dependant on the head work, the cam, the pushrod length and the actual valve guide fitted in the head!!!
If you have any doubt take out the plugs, remove the rocker box and turn the engine over slowly, you should get an idea of the proximity by watching the movement. The only other way is to strip the head and check the underside of the valve spring caps for whiteness marks - hope this helps.
Ian.
the hobbler
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Peter's suggestion to run the engine with the dynamo/alternator/fan belt off is a sound one. By doing this you might eliminate the cause of the vibration if it is in the dynamo/alternator/fan unit. If the vibration still persists, at least you will have eliminated another possible cause, and it is only a few minutes work to remove/re-fit the belt. Just remember not to run the engine for too long with the fan disconnected! I plan to fit an alloy fan on my project'695' engine---and I will be checking its balance before I fit it
Good!......and bad!
Something's wrong there; either a damaged keyway in the pulley, ,loose crankshaft pulley-nut, missing or mis-assembled thrust washer assembly or summat else damaged, worn or wrong.
I don't know if we are looking at chicken or egg....it may be a result of the vibration, but whatever...it ain't right and should be investigated with at least a partial stripdown.
