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MG MGB Technical - Engine 'rumble' and timing

Hi all,

My problem seems to be 2 fold and the first may be related/causing the second.. and may take a little to get your head around!!

Recently the engine (1950cc, stage 2, installed approx 20,000 miles) has started to rumble, with no obvious vibration. At least I believe it is the engine as it rumbles in neutral when the drive chain is not engaged ( it continues to rumble when in gear and driving ). It seems to originate from the front but reverberates right back to the diff, even out of gear.

This rumble has been going on for 'a while' as I haven't had time to investigate and the engine has 'seemed' to be running ok...

My second problem, which has literally only just started, the car would not start yesterday and was imitating a timing issue.

Now, i looked through previous threads, especially at timing related issues to crank pulley delaminating thinking the two issues could be connected, all checked out ok. Timing marks all line up properly at No1 TDC. Coil voltage and resistance ok. Good spark off plug against block when flicking points, etc.

I eventually looked at the contacts in dist cap which were pitted, replaced the cap and the car started, although is not running perfectly by any means, and I don't think it will be long before the issue starts again. Also, I was quite surprised that the cap was so pitted as it was replaced not that long ago. I'm going to replace the points tomorrow, but again these were only replaced a year ago..

My question is one that I'm not expecting a miracle answer to, just some experienced advice I haven't thought of :-)

Is it likely that these issues are connected and the cap/points problem is a red herring?

Any help would be much appreciated!

David
D Fowler

A rumbkle could be a sign of a loose flywheel. Doe it change when you have your foot pressing the clutch?
Sandy
SANDY SANDERS

Not noticeably, it seems to be constant going through the gears - up and down. The clutch plates were replaced last year ( 500 miles ago )but if these had slipped I would have thought I would notice when changing gear...
D Fowler

The ignition problem could be caused by a dead condenser in the distributor.

Thoughts on the rumble: could be loose or wobbling harmonic balancer (crank pulley), loose flywheel, loose clutch cover or worn main bearings.

John
J Tait

Thanks John,

New condenser seemed to do the trick for the timing issue, can't believe have had to replace so soon, only replaced it last year.. would a pitted dist cap knock out a condenser??

I may move to electronic ignition as I'm thinking it would be much more reliable...

I think the rumble must be associated with either the harmonic balancer or water pump (really?) as it 'appears' to originate from the front of the engine around the fan belt area and tails off further down the car. BUT, if it were the harmonic balancer wouldn't the engine run like a dog as everything would be thrown out of balance, including timing?

Now the dist cap/condenser has been changed it runs superbly...

David

D Fowler

New components of any type always have to be the first suspect, quality is pretty dire these days. I've never had points or a condenser fail in service in 40 years. In a fit of generosity a few years ago I did fit new cap, rotor arm, points, condenser and HT leads to my roadster, but never again! The previous set of points lasted 15k without any adjustment, staying within the dwell spec (45D) all that time. The new set fitted a couple of years ago were Unipart and came in a box marked 'TURKEY'. I wasn't sure whether that meant the country of manufacture or was a comment on their quality, but they seem to have been fine so far. I'll not go to electronic until I can't get reliable points any more, electronic has the habit of failing totally when it does, and can only be diagnosed by substitution. Cheap and easy to carry a spare set of points and condenser.

Rumbling was always said to be main bearings, in my experience.
Paul Hunt 2010

David,

The harmonic balancer has no effect on timing except that the marks on it can't be used to time the engine if it has slipped.

I you want to know if it is a belt driven accessory causing the problem, take the belt off and see if the rumble goes away. Obviously don't run it long that way since the water pump will be disabled.

Charley
C R Huff

Paul -

I hear what you are saying with regard to the elec ignition, especially with diagnosing faults. No matter how annoying it is to have 'new' points/condensers going at least they are cheap and easy to change. Although, I seem to be changing them almost on a yearly basis, wether that is down to dodgy parts, being an every day car, or some underlying problem I'm not sure...

Charley -

Of Course, what a simple test! Amazing how one doesn't think of the obvious :) I think I may be clutching on to dear hope that it is something other than the main bearings as Paul says...


D Fowler

I would have thought that if it was main bearings you would have noticed a drop in the oil pressure reading.
What is it reading?
Trevor Harvey

We have an 1820 that rumbles - oil pressure good - burns a little oil - flywheel torqued with new bolts - pulls well - I no longer worry.

The electrical problems are universal - the market is flooded with cr*p kit.

R Walker

Looks like the rumble was down to the water pump!

Problem I now have is there was obviously a slight weep on the gasket which seized one of the long bolts that secured the water pump to the block, so it sheared off when removing. Drilled it out to tap new thread but the bolt seems to have welded to the block nicely and can't tap a decent thread. Looks like I'm going to have to Heli-Coil the hole but wanted to see what peoples experience with Heli-Coiling and which sets are the best. ..

I'm looking at the CHRONOS MASTER THREAD REPAIR KIT UNF 1/4 - 1/2- HELICOIL - www.chronos.ltd.uk/acatalog/Master_Thread_Repair_Sets.html

I know it has more than required for this job, but looks pretty handy to have in the garage. I'm also looking at Ratchet T-bar tap wrench from the same company.

I'm assuming I get one chance to get it right or it's block off, so I'm not worried about over spending on this!



D Fowler

Pretty pricey, but no reason why it wouldn't work. I took an alloy manifold to an engine rebuilder saying I wanted a UNC helicoil, but he put a Metric one in annoyingly. It works, but of course now has an odd bolt.

Copper-grease the bolts!
Paul Hunt 2010

There is a self threading thread insert system that has superseded the helicoil system. I’m not sure what the trade name is. All you buy is the size of the insert you need (comes in thick or thin wall) and a drill for the OD tapping size if you don’t have one. After drilling the tapping size you screw the insert onto a bolt with a nut behind it to lock it, leaving the cutting flutes exposed. Screw the assembly into the hole until the nut bottoms against the surface, unlock the nut, withdraw the bolt and the job is finished.
I use the thick wall self threading insert in aluminium and the thin wall cast iron and steel.

Richard.
RH Davidson

http://www.carrlane.com/Catalog/index.cfm/27825071F0B221118070C1C513E111D081B0006280B1713050245221E0107070F1A3C3B285356445B

This is the site for CARR LANE. They have those inserts
Sandy
SANDY SANDERS

Carr Lane is a good product. I'M sure I'll get flack on this, but I think their stronger than Heli-Coil. But, remember if it's a blind hole, to blow out the hole with air just before bottoming out the collar. You have to remove the drive bolt to do this, then re-insert the bolt and bottom out the threaded collar. Keeps from compacting shavings if the intended bolt goes in too far. Just a suggestion.
Paul Jennings

The solid inserts are fine, BUT they take up significantly more metal. So, if you ate doing a thin walled boss, helical inserts are better, or the only possible thing. Also, as the boss walls get thinner, or on old and suspect castings, self threading devices can put a lot more stress on parts while being installed.

FRM
Fletcher R Millmore

Thanks everyone.

The Carr Lane product certainly looks good but went with the Chronos Heli-coil kit in the end, as needed quick turn around for MOT re-test. Certainly recommend this company; professional, quick and efficient service.

Worked a treat! And now no rumble!!

Back to being a happy MGB owner - for the minute anyway!

David
D Fowler

This thread was discussed between 11/03/2010 and 26/03/2010

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