Engine woes! - SORTED! But another problem has arose!!!

Mossy68 · Post by **Mossy68** » Sun Jun 15, 14 9:32 pm

Was your compression test done with a warm engine and carb at WOT ?
I think minimum pressure should be about 100psi with no more than 25psi difference between cylinders ?
Blocked pcv valve ?

I used to check my bike for vacuum leaks with a tin of easy start. Spray little bursts around hoses etc and see if idle picks up. ( obviously being carefully not to allow the spray to be dragged in air intake )

sinny · Post by **sinny** » Sun Jun 15, 14 9:42 pm

Motor was cold for the compression test (burnt my hand badly trying to do it with the motor warm.

PCV is new. I do have some smoke coming out of the breather which I thought was condensation but it was still coming out after the motor had been running for 20 minutes.

Carb is only a few months old & she's only done 3 miles. But has been run in the garage lots of times.

Mossy68 · Post by **Mossy68** » Sun Jun 15, 14 9:47 pm

I'm stumped then mate.
I've listed all I would check.
I'm sure the clever lot will be along soon

sinny · Post by **sinny** » Sun Jun 22, 14 3:37 pm

Well I've sorted the running issue out!

I noticed the fuel filter before the carb wasn't staying very full. I had a fuel filter just before the fuel pump as well as the one just before the carb & it seems the one just before the pump was just too much! I've removed that & away she went. Running nice & smooth?

However! She's developed a vibration (almost a pulsing) between 25mph & about 45mph. Feels like it's coming from the back of the car. Did it in 2nd 3rd & neutral.
Haven't noticed it before, has all new bushes, shocks, uj's, wheels, tyres etc. I did drop the front end by an inch or so but as I said it feels like it's coming from the back. Any Idea?

MilesnMiles · Post by **MilesnMiles** » Sun Jun 22, 14 6:25 pm

I would return the ride height to where it was first and see if the vibration disappears.its a long shot, but you may have altered the pinion angle of the diff to prop depnding how much you lowered it.
Also, wild card idea, but do you have. A pinion snubber fitted and is it now hitting the floor.

sinny · Post by **sinny** » Mon Jun 23, 14 7:18 am

I haven't got a pinion snubber. I was thinking the same thing about the height, I'll have a play around.

Charger · Post by **Charger** » Mon Jun 23, 14 7:33 am

sinny wrote:has all new bushes, shocks, uj's, wheels, tyres etc. I did drop the front end by an inch or so but as I said it feels like it's coming from the back. Any Idea?

maybe wheel bearing or diff?? or trans??

MilesnMiles wrote:I would return the ride height to where it was first and see if the vibration disappears.its a long shot, but you may have altered the pinion angle of the diff to prop depnding how much you lowered it.

he said front ride height, that wouldn't alter any relative diff/prop angles at the rear

MilesnMiles · Post by **MilesnMiles** » Mon Jun 23, 14 9:01 am

If the car has been lowered it will allow transfer of weight to be different from where it was before. If, and I stress if, there has been a marked change in the angle that the UJs operate at it will cause pulsing, surging in the way described.
It takes just a few minutes to return ride height to where it was to check the difference.

I nicked this from a Chevy forum, but...
'When using constant velocity U-joint driveshafts, both ends must be at the same angle (0° difference) to maintain constant velocity. Any angle difference, positive or negative will cause driveshaft U-joint binding with pulsing and surging. This will eat U-joints over time and the vibration, pulsing and surging will cause traction loss and the binding will slow the car. '

Dave-R · Post by **Dave-R** » Mon Jun 23, 14 11:36 am

Charger wrote:he said front ride height, that wouldn't alter any relative diff/prop angles at the rear

Correct. The UJ angles are measured relative to the axis of the pinion and the output shaft of the gearbox.

The only time a change to ride height can effect the pinion angle is if the rear axle is moved up or down reative to the chassis.

The front suspension has no effect on this angle at all.

Dave-R · Post by **Dave-R** » Mon Jun 23, 14 11:41 am

MilesnMiles wrote:'When using constant velocity U-joint driveshafts, both ends must be at the same angle (0° difference) to maintain constant velocity. Any angle difference, positive or negative will cause driveshaft U-joint binding with pulsing and surging. This will eat U-joints over time and the vibration, pulsing and surging will cause traction loss and the binding will slow the car. '

That is 0 degrees when driving. Not stationary. When driving or accelerating the nose of the diff raises slightly. So to compensate for that the diff has to be set very slightly "nose down" to the correct angle.

Again this is not "nose down" relative to the floor as some people assume.

Dave-R · Post by **Dave-R** » Mon Jun 23, 14 11:45 am

Simplest diagram there is.

Dave-R · Post by **Dave-R** » Mon Jun 23, 14 11:47 am

http://www.carcraft.com/howto/91758/

sinny · Post by **sinny** » Mon Jun 23, 14 1:33 pm

Well I haven't changed any angles in the rear & no movement in the rear whels so I don't think its a bearing.
It still does it in neutral so surely this would rule out the trans?

Maybe the diff is duff. looked at it earlier & it was low on oil.

Dave999 · Post by **Dave999** » Mon Jun 23, 14 2:34 pm

don't see how lowering the car is going to have too much impact on pinion angle

centre of gravity is a tiny fraction further forward but no more or less than having a fat fella sit in the front or back

check you haven't flat spotted the tyres with it standing
tyre bulge
are the brakes dragging?
have you got a stone in the tread
anything rubbing

exhaust tail pipe vibratuing on the chassis leg once hot

exhaust gets longer by about an inch when hot pulls on the mounts and can hit

Dave

sinny · Post by **sinny** » Mon Jun 23, 14 10:03 pm

Checked all that Dave & all was good but it does look like the exhaust was touching the rear chassis so sorted that bit it was too strong a vibration to be the exhaust.
also raised the front end back up by half inch just to check it although pinion angle looks good.
Wont get a chance to try it until Wednesday though.