Cold start rattle

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niftyrodman
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Cold start rattle

Post by niftyrodman »

Motor is fairly newly reco, (948 A motor) and Ive plastiguaged the big ends twice, and if anything one may have 3-4 thou instead of 2 Motor runs quiet as a mouse otherwise. A technical point that maybe someone can enlighten me, is how much big end clearance, would allow that to happen as a guesstimate. I mean I have had engines with noisy bearings on acceleration, but they never rattled cold. Im puzzled
Murrayminor
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Re: Cold start rattle

Post by Murrayminor »

Is it definitely a bottom end rattle?
I would think a bottom end rattle will be there all the time whereas a top end rattle could occur due to a drop in oil pressure.
Proud owner of my first Morris Minor
philthehill
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Re: Cold start rattle

Post by philthehill »

The BMC wksp manual quotes the big end diametral clearance for the 948cc engine as 0.0006" - 0.0016".

The 1098cc engine diametral clearance is quoted as 0.001" - 0.0025".

I suspect that the oil is draining from the bearing when stood and as you have excess clearance the oil takes longer to build up in the bearing resulting in the rattle. Once the oil has built up and the pressure stabilised the rattle goes.

I would also suggest that you measure the crank big end journal (at more than one point) with a external micrometer and use a internal micrometer to measure (at more than one point) the internal dia of the conrod with shell bearing fitted.
Whilst Plastigauge may be good you cannot beat measuring with a micrometer.
Phil

oliver90owner
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Re: Cold start rattle

Post by oliver90owner »

I know nowt about the bottom end of these engines. I would be checking the centre main bearing. It is likely out of spec. I had this on a 5 bearing crank which rattled until the oil pressure built up at a cold start. Only lasted a couple of seconds but indicated big trouble ahead (especially the way I used it).

With 4 thou on the big ends and likely some degree of ovality I would expect it to knock rather than rattle. Oil pump or pick-up may be suspect too.

You say ‘fairly new reco’. That can mean a lot of things. Fitting new precision bearing shells to a worn crank means little to me.

You don’t say how long this ‘rattle’ lasts. Is it temperature dependent? If so it could be small ends or even piston clearance.
niftyrodman
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Re: Cold start rattle

Post by niftyrodman »

Yes, I think sometimes hope distorts diagnosis. I will start engine cold with a random plug lead off, every morning until I locate the bearing in question, I will then measure that crank journal and the rod end, as you suggest, and buy a set of .002 bearing shells and fit a pair to that particular rod. That is of course if the measurements suggest that option. Thanks Phil.
niftyrodman
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Re: Cold start rattle

Post by niftyrodman »

oliver90owner wrote: Wed Apr 15, 2020 9:39 am I know nowt about the bottom end of these engines. I would be checking the centre main bearing. It is likely out of spec. I had this on a 5 bearing crank which rattled until the oil pressure built up at a cold start. Only lasted a couple of seconds but indicated big trouble ahead (especially the way I used it).

With 4 thou on the big ends and likely some degree of ovality I would expect it to knock rather than rattle. Oil pump or pick-up may be suspect too.

You say ‘fairly new reco’. That can mean a lot of things. Fitting new precision bearing shells to a worn crank means little to me.

You don’t say how long this ‘rattle’ lasts. Is it temperature dependent? If so it could be small ends or even piston clearance.
Well I think I posted my problem half cocked. The crankshaft was ground, the engine has not done 10 hours since installation. I am not sure what the actual crank diameter is, as its been a long time since it was done(familiar restorers problem) When the engine was first started and several times later, there was no noise on start up. Then this knock appeared. No overheating, as the car has not been on the road. Ovality is out, the shaft was ground, and having had the sump off twice chasing this knock there is no sign of any damage, or excessive scoring etc As I said to phil I plasti -guaged the journals and that didnt reveal, any excessive clearance. The block was rebored and the piston are new. I will reveal the problem bearing by starting it with a plug lead off one by one, when it is cold. Now, say the crank is .010 undersized, n my problem will be getting some bearing shells 012 undersized which may be an impossibility. If that is the case I can either shim the cap, or just live with it, unless you kind chaps can help.
philthehill
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Re: Cold start rattle

Post by philthehill »

Do not shim the cap otherwise you will do more damage. Shimming the cap increases the clearance and should never be done. Also the bearing cap contact faces should never be reduced or altered.

Forget the Plastigauge and do the job properly with a micrometer. It is the only way to get the right measurement.

Just because the crankshaft has been reground does not make it right.

Phil

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Re: Cold start rattle

Post by kevin s »

Ours does something similar, after fitting the electronic ignition etc it starts instantly and I get a couple of knocks and then it's fine, I try to remember to turn it over for a second or 2 with the choke in then pull it out this primes it enough not to knock, it has 35psi oil pressure at a hot idle and was recently reconditioned (no idea how well though). I was wondering if fitting an adaptor / modern filter with an anti drain valve may be a solution.
niftyrodman
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Re: Cold start rattle

Post by niftyrodman »

Thanks Phil.It sounds about right for a big end. It is a knock/rattle I think the main knock would be deeper. I tried start with No4 lead off, and the noise was still there but much muted. Tomorrow No3 . Its a restorers inspiration killer, these things.When I assembled the engine I should have checked the shaft journals and the rods. Hindsight.
niftyrodman
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Re: Cold start rattle

Post by niftyrodman »

I quizzed the reconditioner mainly about getting an odd set of bearings .002, or .003 under whatever size is in the engine, and thats possible.
He said it doesn't sound like a bearing if there is no noise hot, and I cant argue with his hypothesis, so as I progress eventually to single out the cylinder with the problem, I will oil it up, night before and test in the morning. If it is a piston, its going to be quiet. If it is the bearing it will be noisy..
kevin s
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Re: Cold start rattle

Post by kevin s »

It could be piston slap, ignition timing affects this, try retarding it a few degrees to see if there is any change.
niftyrodman
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Re: Cold start rattle/knock

Post by niftyrodman »

Starting the engine with No.3 Lead off the plug, it was quiet. So Ive squirted 8 oil can squirts of 20/50 oil into that cylinder and I will leave it and start it tomorrow morning, and see what happens. If it knocks, I have an over clearance number 3. big end bearing. And in theory it should be a little louder. So, if the Reconditioner Mathew is right it will be quiet. What do I think? I think it is the big end. We will see. I thought about this, and also wondered why I didn't have a knock when the motor was hot. I believe that with 40+ psi oil pressure the extra clearance is not enough to show up hot, we will see.
niftyrodman
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Re: Cold start rattle

Post by niftyrodman »

Goes to show reconditioners can be wrong. Its all about oil pressure, and its interesting. Knocking on No3 with lead back on plug. Sump off again, measure properly, ( thanks Phil) and hopefully I have an all round room for a .002 under shells. I don't mind buying a set, as they will be used eventually. Clearance allowing rattle must be .004 and a half. Gee, never thought that possible to be enough to cause noise. If I know the original crank dia, and note the undersize on the bearing cap, I should be able to work out what the rod end/crank clearance has been, hopefully I can get the rod low enough to measure it, but the lesson learned here is that the crank rod clearance when setting up a reco, is obviously critical.Maybe in this case, the offset at the rod end, could be a mitigating factor accentuating the movement?
kennatt
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Re: Cold start rattle

Post by kennatt »

check the oil pick up pipe,From memory I remember someone having same problem and discovered that if you overtighten the pipes bolts on the bearing cap it can distort the pipe fitting to the block and cause an air leak until oil circulates,take pipe off and refit may just be the problem.
Pretty sure this was on a minor but could have been on mgb.
niftyrodman
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Re: Cold start rattle

Post by niftyrodman »

Thanks Kennet. The thing is the noise disappeared when I disconnected the plug lead on No3 before starting the engine cold. Completely. So oiling up the pot, would change a piston noise, which I did and the knock persisted. Im amazed, because its only a couple of thou over what it should be.At the most .004,so Im pulling off the sump and miking the shaft and rod( the shaft was ground, its only done a few hours running if that) Hopefully I can resolve it properly, as the last thing I want is to be pulling the motor apart again so soon. So thanks for your observation
kennatt
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Re: Cold start rattle

Post by kennatt »

do you know the history of the block prior to reconning ie was no three big end knocking before. I say this because(although not common on A series)certainly on the B (Most of my rebuilds on MGs) If there had been a lengthy big end knock or a run bearing it was advisable to change that particular con rod because there was a chance that they had been knocked out of oval at both big end and little end. Had a couple like this that knocked after a very short run time after a re con. One a big end the other a little end. Worth a good check of both. good luck
oliver90owner
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Re: Cold start rattle

Post by oliver90owner »

Also, if the rod journals have been ground under-size, you likely need to check the mains as well!

I remember, but not all the details, of putting an engine in an Escort about 70 miles from home one weekend. Fitted in a cowshed after the engine had been hastily put together in a dairy. Found oil pressure light would not extinguish until quite a lot of revs. No knocking or rumbling, just no oil pressure. I drove that car the 70 miles home at about 4000rpm, as I recall, to keep the oil warning light off (and a bit).

Found the main bearings were the right size for the crank but the block had been line-bored to +15 thous. A change of bearings sorted it with no damage done.

About twelve years ago a friend was having trouble with oil pressure for a Fordson Major diesel engine he had rebuilt. It took me less than ten seconds to diagnose his problem - the same as I had been caught out with back in the 1970s! He was no more amused with the bearing supplier than I was, when I was supplied with the wrong bearing shells.
niftyrodman
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Re: Cold start rattle

Post by niftyrodman »

Thanks Oliver. The main journals were ground as well. The whole thing is, if you have a knock, and you can stop it by disconnecting a plug lead, on start up,then one can assume that normal combustion pressure etc is going to increase the load on the conrod crank bearing, and if the noise stopped when oil pressure rose, it does seem likely that the up and down forces if not insulated by oil pressure, when there is too much clearance between the bearings and the crank a knock can be heard. I cant explain the physics of why this engine doesn't knock when it is hot, as it would make a lot of sense. If I don' fix it now over time it will hammer out the bearing .
oliver90owner
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Re: Cold start rattle

Post by oliver90owner »

I think you may have missed my (too subtle) point?

New mains, out of spec may not show up in the short term - but if that crank has under-sized mains, as well as under-sized big end journals, it would be better to check out now and avoid problems in the nearer future than one should expect for a reconditioned engine.

My engine problem, back then, was simply far, far too much clearance between shell and crank - 15 thou, not just 2 thou. but it was fine at 4000rpm for 70 miles of gentle driving. It would not have lasted long if driven in my usual manner - yes, I often used full torque and power for prolonged periods🙂. I shifted to 5 main bearing engines (from 3 bearing cranks) as those with 2 fewer main bearings would not withstand the hard work expected from them.🙂 Also the bigger mills had a lot more grunt than a tuned 1200 engine.
kennatt
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Re: Cold start rattle

Post by kennatt »

it dosent knock when running because the oil is now up round the system,after a longish stand if there is any wear in the bearings,mainly the mains, the oil drains back so on start up you get the dreaded death rattle. a few years ago I was informed that a couple of escort owners had wired the ignition via the oil pressure switch so it couldn't start until pressure was up.Apparently ran this way for years without the need for a re con.My initial thought was that it should be the engineers problem to sort out,but then since you did the re assembly that would probably leave them with an opt out.
I don't really follow your reasoning re fitting different shells If the crank has had a regrind then the shells supplied by the engineer will be oversized by the same amount ground off the crank .That figure for the grind would have been limited to the sizes of shells available. So the shells you have SHOULD be the right ones for the crank. So the marks on the caps should match the size shown on the back of the shells. If on checking the crank you should be able to work out how much has been ground off from the standard and then check the shells ,if these don't match then back to the engineer,and lets hope he has ground the crank equally again check them all :o
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