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MG MGA - Start Up Vibration
Finished a rebuild of 1600 motor and reinstalled. Have done the initial startup all went ok, pulled the plugs and colour is good. There was a small water leak from the thermostat housing and the exhaust manifold to exhaust pipe has not seated correctly. I have fitted MGB exhaust headers.
The motor was rebuilt 0.010 u/s main and big ends + 0.020 rebore and 0.020 o/s dished pistons. Flywheel weight has been reduced by approx. 7 lbs. Pressure plate, flywheel, crankshaft, con rods all balanced. Front pulley is cast iron from an 1960 Austin Cambridge(?) 1500.
On a test drive today I could feel a vibration at around 1500RPM that disappears aboutr 2500RPM , which seems to come from the engine. Fan is original and refitted from the previous 1622 motor which had travelled about 50,000 miles since my ownership. Incidentely never felt this vibration with the other motor.
Wondering if the vibration could be the (1) the fan as I did not mark orientation to the fan hub on disassembly (2) the front pulley - being the earlier non-damper cast iron type or (3) I have managed to orientate the pressure plate to flywheel 180 degrees. It was marked by the balancer....and I am sure it is correct but................ (4) something else I have managed to put together incorrectly.
One other observation;
I set the timing statically and then adjusted it at idle by moving the distributor to get the smoothest idle then backed off slightly. On checking, this lined up with a mark I had on the distributor clamp plate. The distributor is from the other (1622) motor, although it is the correct 1600 distributor. When I checked the timing with a setback timing light this showed 53 degrees advance at 1000 RPM...........I can't see how this is possible. Given the engine starts easily, does not run on at switch off and the plug colour is almost perfect. So I am assuming my timing light is giving a false reading.
Any thoughts on the vibration and the timing
|R J Goebel|
|My first thing to do would be a check with another timing light. This appears to be way too high.|
Many modern timing lights with adjusting advance don’t work properly with positive ground system. I have two timing lights with the same problem. I suggest you to place a paper degree scale on the front pulley, set «0» timing advance on the timing light and read the result on the paper scale.
I hope it will work out.
|Just take the compliment of the angle on the dial back light. In this case the actual advance would be 37°, very close to what it should be at 3000rpm, which would indicate an incorrect initial setting or a week advance spring. Cheers - Dave|
|And to follow on from the other comments the vibration is pretty sure to be predetonation due to too much advance and /or weak mixture. This will eat your pistons rapidly if left unsolved, so do your new engine a big favour and dial back the advance and set the carbs a few flats richer and the problem will probably disappear|
Thanks for all the quick responses.
Sandy, I've had the timing light for about 10 years last used on the previous 1622 engine back in November, also used it on other cars in the past with no apparent problems. Maybe it has finally given up, so worth a check.
Nick, I should have mentioned that the car has been converted to negative earth also have modern type leads.
David & Dominic, the dizzy was taken direct from the old engine where it worked ok. I had it stored in a box while rebuilding the new engine so something might have come adrift..........will have a look today.
|R J Goebel|
|Just something to note: The 1622 crank is completely different crank throw positions than the 1500 and 1600. (Maybe what your feeling is the difference?)|
The distributor on the mk2 1622 is marked DM2.
There is a date code on the side of the distributor that will give the month and year.
I was never sure if the curves differed but if a distributor happened my way that I could confirm was around of the build date of the motor I was rebuilding.I always used that one to get refurbished.
I dont think any of this information helps you diagnoseyour vibration problem.
I think that it could be the the flywheel - clutch assembly if it was alined improperly after balancing.
Wish I had better news. Thatll be a job to tackle but Try the easy stuff first do what you have to do!
I was thinking the same regards the 1600 vs 1622, maybe the later engine is a bit smoother. I have never driven another MG with a 1600 engine, however have driven a 1600 Mk2 some years back, from memory it was reasonably smooth.
David & Dominic, I pulled the dizzy today and there is some movement of the mechanical advance before any resistance is felt against the spring tension. The dizzy date code is 6/59 and it is marked 40510D so appears to be correct for the 1600. When I installed this dizzy in the old motor about a year and 10,000 miles ago there was no movement of the mechanical advance without any spring pressure....perhaps thats what you get with 50+ year old parts.
I have some new springs will install them tomorrow and see what happens.
|R J Goebel|
|To get back to basics with the timing - I suggest you check out the manual and statically time it with a 12v bulb - that always used to be close enough. The strobe can come later. That vibration surely must be something else.|
When assembling the flywheel to the crankshaft, did you check there were no burrs on the crankshaft flange where it enters the flywheel and did you then check the flywheel's clutch face ran true when the crank and flywheel were turned? We must assume you are happy that the flywheel really was balanced.
You say you felt vibration when driving. Do you get the engine vibration when stationary? If only when moving, the vibration could very well be the propshaft, which could be out of balance or incorrectly orientated at the sliding joint??? As I'm sure you will appreciate, the U.J's must be in correct orientation to each other.
|P N Tipping|
The excessive distributor advance turned out to be wear in the advance plate. The plate "tension spring" between the upper and lower plate had worn a grove and caused the plate to stick. The vacuum was disconnected however the plate was not in the correct position. Replaced the vacuum plate reset the timing and all now ok.
The vibration turned out to be (1) loose fasteners on the MGB headers fitted to the car, this combined with (2) fitting of the modified heat shield directly onto the inlet manifold and was resting on the exhaust manifold. Previously the heat shield was fitted after the spacer allowing clearance from the exhaust manifold.
The new 1600 motor is now running ok, however seems "rougher" than the previous 1622 which was bored 0.020 fitted with a standard cam and standard 1600 (heavy) flywheel. Also had an MGB damper pulley.
The current 1600 bored 0.020 has a modified cam with more duration and lift - not as much as a Crane cam (about ½ way between standard and the Crane Cam as sold by MOSS). The flywheel has been lightened by about 7 lbs with a standard MGA clutch and pressure plate. Also have a cast iron front pulley - from an Australian produced Austin Cambridge - which is somewhat heavier than a standard MGA pulley.
Is it possible the MGB damper pulley would make the motor feel smoother? If so then I will switch the one off the old motor along with the front cover (with oil seal).
|R J Goebel|
Hi Russell, I have a 1600 engine in my 1960 coupe that was rebored to 1622 + 30 thou and fitted with early B con rods (same as 1622). The flywheel was lightened to MGB spec plus another 7 lbs. The engine was balanced. The car drives very well and pulls like a train, but I do have a vibration at certain revs on the engine.
Initially I had a B front crankshaft pulley/damper and noticed a slight vibration between 2400-2800 rpm, which is annoying. I installed the Aussie made crankshaft pulley/balancer and this helped a little and fine tuned the vibration to 2500 rpm. I now have a buzz on the gearlever at 2500 rpm only, otherwise it's ok.
The Aussie balancer is not cheap but you can find them on eBay for a better price.
|Andy Preston 1|
This thread was discussed between 17/02/2014 and 21/03/2014
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