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MG Midget and Sprite Technical - Bad news bad news

Ok so after sorting the breather issue I started tuning my newly rebuilt engine.
At idle the engine is really smooth on its hif44 and comes up to temp great with great oil pressure. Good so far.
Then I give it a bit of gas. Revs rise nicely and then blue white smoke (not much) starts coming out of the Exhaust.
Damn. Disconnect the breather. Still smoke.
Blip the gas and big puff of white/blue smoke.
Give it more gas steadily this time. More smoke than idle but less than when blipping. Raise the revs some more to 3000. More smoke and a spark out if the exhaust! Drop back to idle. Still smooth.
What's going on !
I rebuilt the engine after + 20 rebore. Head has also been rebuilt and resurfaced. Doesn't seem to be a pressurising the water system.

Thoughts. ?
Quite pissed. Last stage of 4 year rebuild. Might just burn the car!!!
Tim
T Dafforn

no worries, i would suggest driving it for 1000 miles or so
a.o. arnold

I think more detail is needed and you need to clarify whether the smoke is oil or coolant based. If the engine is new then the blow by due to the rings can be severe but they bed in quickly, 100 miles or so in my experience, so maybe your breather system is being overwhelmed. What type of breathers or PCV is the engine using. I have also experienced a pin hole leak from the coolant passage into the intake tract that led to major white smoke plume from the exhaust from what looked like a small quantity of water when peering into the effected inlet tract.
David Billington

I had something similar with a 1275 midget. It turned out to be mice had built castles in the exhaust and the sparks were burnt mouse bedding (I guess).
After removing complete exhaust and cleaning the smoke and sparks were no more.
Sandy
DARNOC31

Interesting. Thought this might explain the spark as the exhaust system is old and has been sitting in the garage in 4 years.
I have a new second hand Peco system that I need to fit.
Re PCV. see good news bad news thread. All the stuff I mention was with the pcv disconnected.
Pinhole leak possible. Will bypass warming tube.
Tim
T Dafforn

Dissing the crank breather pipe obviously eliminates the timing cover and oil sucking.

I take it you then blanked off the pipe so you didn't have a massive air leak, or are still on the PCV? Plug it anyway just to be sure.

More revs, more smoke. More suction on the inlet. If it was 'only' a cloolant leak I think it would be very obvious if it was only steam. But You say white/blue smoke and a spark from the exhaust. Was this accompanied by a loud misfire? Does it run smoothly above tickover?

Is there oil in the water, or vicky verkcy?

Lawrence Slater

Is there oil being shoot out the small vent hole in the oil filler cap, While its smoking out the exhauste ???

I tend to agree... the rings need to bed in, the part that worries me is the white smoke, ....

If it continues and gets worse... id put a vacume gauge on to the intake manifold and see what that indicates

Prop



Prop and the Blackhole Midget

It could well be its just a new engine...and the rings need to bed in

Is there oil being shoot out the small vent hole in the oil filler cap ????

My 2nd thought ...without reading the other thread....you may not have a funtional oil sperator, and the fine oil mist is being drawn into the carberation

Prop
Prop and the Blackhole Midget

Sorry... avoid my last so called post... the BBS is resurrecting dead smelly pre edited postings agian that should have stayed in the trash can where they belong

Prop
Prop and the Blackhole Midget

When I said white smoke it was more an indication that it was bluey white.
Cheers
Tim
T Dafforn

Tim,
I am puzzled as to why, having sorted out your PCV system, you now appear to have disconnected it again in order to test run the engine? Or have I misunderstood the sequence of events?

If the white or bluey-white smoke is coolant leaking into the engine then it will smell distinctly of hot antifreeze. A sort of sweet, sickly smell. Even if you have filled the cooling system with just plain water, white smoke would smell distinctly of steam.

The bluish colour would suggest that it is oil. And it may be nothing more serious than oil getting past the rings and into the cylinders if the rings haven't bedded in yet.

I understand it is a newly rebuilt engine. What running in procedure are you following? Don't be over-gentle with it at this stage or the bores will become glazed and then the rings won't bed in properly, and your oil burning symptoms will persist or get worse!
Guy W

Guy,

My experience is that the engine will smoke when started the first time but once the assembly lube has burnt off it won't smoke due to the rings having not bedded in, piston blowby is another thing and settles as the rings bed in over a 100 miles or so . I have a very interesting book called "The component contribution engine progress through the specialist manufacturers" and it states that the amount of oil that passes the rings with each rise and fall is actually quite high but what effects whether an engine burns oil is the way the rings pass oil. Due to the ring profile the ring may pass oil better in one direction and so a ring that passes oil better as the ring goes down the bore will effectively pump oil into the cylinder leading to oil burning. Ideally the ring passes oil better as it travels up the bore so the net result is little retained oil in the combustion chamber to contaminate the combustion.
David Billington

Thanks David,
I know from when building engines for my rally mini in the 1970's we used to refer to the oil rings as "scraper rings". They were supposed to "scrape" oil off the bores as they travelled down so as to limit the amount left to burn off in the combustion chamber. A newly rebuilt engine would often smoke until the rings had bedded in as the cross hatched surface retained oil a little too well. That was my experience anyway, but I don't claim to be an expert.

From what you say of the rings passing oil in one direction better than the other just makes me wonder if the compression rings are in fact fitted the right way up. They usually have a slight taper to them.

The other thing that may be causing blue smoke is oil from the valve guides. Possibly from the exhaust valves if there are seals on just the inlets and the engine has a non-standard cam.

None of this would explain the sparks from the exhaust!
Guy W

This is the 2nd head you fitted Tim, wasn't it? So new guides and valves?

I've never built an engine that didn't smoke a little on start up, but only for a few miles, and not as being described. Certainly not 100 miles. I re-ringed my worn 20+ with cords, and they take a while to bed in, but it hardly smoked at all.

Of course we aren't seeing the smoke. It may seem to be a lot, but may actually be insignificant. However accompanied by sparks from the exhaust suggests somethings amiss.

HG failure? Crack in the block face?
Pull the inlet and exhaust manifolds and see what's in the ports. If there's oil in the exhausts, you have to dig deeper.

Lawrence Slater

As aforementioned, why after so much debate is the PCV off? If blue smoke then more likely to be oil - any deposits in the exhaust?

Problem solving is essentially a process of elimination. Change one thing, if it does not work, revert to previous condition and try something else.

Piston rings passing may be one theory, and as Guy says, they are usually fitted with the stamp on the ring facing upwards due to the taper. Valve guides certainly another viable theory...however, personally afte ran engine rebuild, I would do the most simple thing and just give it a run to allow things to bed in and settle down.



Mark O

Woooohhhaaa,

""Sparks out the exhauste""

....good catch guy, I glossed over that one...this thread just got a whole lot more interesting

My guess is a busted piston ...most likely the piston ring landing, Wow, ive been there, and done that....not fun

In my case I used the haynes manual spec.for the ring gap, which was way WAY differant from the new AE piston specs for ring gap...once the rings fuse, there goes the landings imediatly after

Granted...im just guessing at that, but for sparks to be shooting out the exhauste something had to go wrong inside the cly. And burning oil just backs up my guess

If there is oil mist shooting thur the vent hole in the oil filler cap like I asked above....then your 3 for 3

I had a 6 foot oil geyser when I broke the front 2 pistons

I feel for you buddy, I really do, hopefully the cly survived okay... if so its just a fast hone, new piston set and the rods re-rounded back to true, And a new head gasket

Good luck....ill see if I can find some pics of my adventure

Prop

Prop and the Blackhole Midget

I've seen sparks out of the exhaust on my car before and having just been for a high rev blast and pulled up I wasn't worried and the engine was fine. I put it down to the build up you get on the back of the inlet valve breaking off and burning up through the engine. I had noticed in the past when cleaning valve that often the build-up is uneven where sections have come off. On a new engine with clean valves I would be more worried as to the cause.
David Billington

Hi Lawrence et al,
Second head, first one that had been reconned..
Pretty sure that the rings are all the correct way up (checked and double checked) when I assembled.
ring gaps were checked and were in spec with the book, but prop's comments now have me worried..
Hopefully spark could be just the result of burning dust etc from the exhaust as it was left in the shed for some time..
regarding disconnecting the breather, I am still not sure that the PCV is working as it should..
Will have to summon up some strength to take the head off again!
Tim (tired!)
T Dafforn

Well...
took the head off (getting good at this < 20 minutes!)
heres what I found...
oil in the inlet manifold
oil in 3 out of 4 of the exhaust tracts (front just a bit sooty)
cylinder bores fine
small puddles of oil in each of the cylinders..
thoughts?
To me this means something up with rings? seems strange as I would have had to have put all the pistons/rings together wrong?
Possible I suppose, but not had the issue before.
Cheers
tim
T Dafforn

Tim,
Before you take the head off, what do you hope to discover by doing so?

If you are getting blue smoke with the PCV and breather hoses disconnected, then you know that the blue smoke (i.e. oil) is not coming from the crankcase and therefore not from piston ring blow by. NB Lawrence pointed it outr earlier, but if you do disconnect the breather hoses you MUST plug the connection into the manifold.

I forget - yours isn't the engine that someone has added an extra breather hose between the rocker cover and the air filter is it? That won't help at all.

That leaves either oil left on the bores by the oil control ring (the oil scraper). This is typical of a new engine where the rings have not yet bedded in and there is a good chance that it will improve with further mileage.

Where else could it be coming from? Possibilities are cracked head or even cracked cylinder wall, but both are relatively unlikely and I would totally ignore that for now.

The other possibility is that this is oil drawn down the valve stems from the rocker cover. On A series engines this is usually dealt with valve stem seals on just the four inlet valves. But if you have a non standard cam then the valve overlap can result in pulses of negative pressure (suction) in the exhaust tract and this can draw oil down the valve stems. The solution is to add stem seals to the 4 exhaust valves as well.

Guy W

OK Tim, I was typing at the same time as you. The easiest thing would have been to do a compression test before you removed the head. That would have highlighted any piston ring problem, But its too late for that now!

Oil as you describe it could be coming down the valve stems as I described before. Do you have stem seals on the inlets? Do you have stem seals on the exhausts? The puddles of oil in the exhaust tracts is exactly what you get when oil is drawn down the valve stems into the exhaust valve chamber. Unlike the inlet valves which then suck oil into the cylinder, on the exhausts it collects in the outlet tract where it will vaporise and create a blue smokescreen in the hot exhaust.

At this stage I would definitely add stem seals to the exhaust valves and then put it back together for another trial.
Guy W

Hi Guy,

Guess it was a bit of a knee jerk reaction to Props comments. That last thing I wanted was a chipped piston gland and scored piston..

Regarding the breather, yes I plugged the manifold end..
Given that there seems to be only oil I am guessing that it is probably not head gasket (the water that came out was clean as a whistle)..

All the valves have stem seals and new guides so cannot be coming from there..

the only issue I am concerned about with running it in is that to me the smoke was enough to fail the MOT which would mean I wouldn't be able to run it in..

Hmmm..
tim
T Dafforn

Tim,
New valve guides may well have a wider tolerance than as originally specified if they are for unleaded specification. So they are even more prone to oil seepage down the valve stems. So don't rely on new valve guides to control oil seepage.

Are you sure that all 8 have stem seals fitted? Is that what you or the engine builder specified? It isn't standard. It can be quite difficult to see the stem seal hidden behind double valve springs.
Guy W

Hi Guy, Like your thinking but I am pretty sure I fitted valve seals to all 8. Just been out to the garage (paranoia that I left them out when I rebuilt the head with the swiftune double springs). The are there.
Interestingly I never considered that you wouldn't fit them to all valves.. Mind you the last engine I rebuilt was a lotus twincam and that has no seals..
Cheers
Tim
T Dafforn

O yes,
I should have said, considered doing a compression check but Props comments were in my ears and I didn't want to risk running (even on the starter) if the pistons were in the process disintegrating!
Cheers
Tim
T Dafforn

Tim

An unusual one but it can happen:

Are you running a high lift cam? We have had cases where a combination of valve guides a bit too high in the head and a high lift cam has resulted in there being very little clearance (about 20 thou) between valve cap and seal at full lift. Result was oil pumped past the seal and into the guide.
Paul Walbran

The stem seals need a close inspection. The original ones not only tend to work harden,but are also prone to losing the little spring ring that helps to grip the stem. My vote would be to never reuse old seals, but fit all 8 with the later Dupont Viton ones, and once fitted make sure they have a full valve spring working clearance.
F Pollock

Tim,
Another line of inspection to consider is the condition of your rocker shaft and rocker bearings. If there is excessive wear, especially in the shaft, then oil will be pumped out into the valve area faster than it will drain back down to the sump. The oil accumulates and if it overtops the valve guides in the head, then suction of oil down the valve stems is greatly increased. Coupled with a missing or damaged or ill fitting seal would allow oil loss.
In theory this might explain the oil in exhaust ports #2,#3 and #4 but not #1 as the engine slopes slightly to the rear so the back 3 would get oil swamped first.
Guy W

New seals throughout. Didn't reuse anything apart from the crank , block, head, and rockers. Even the con Rods were replaced!
Ok, have a clear head this morning.
To me the oil an only be coming from 4 places.
1) past the pistons
2) past the valve seals
3) past the head gasket
4) crack in the head

4 seems unlikely as I have tried 2 heads. On with new springs and stem seals but not refaced. One completely rebuilt using the springs from the first and new stem seals.

3 would have led to oil water mixing which I haven't seen.

2 again have used two heads both with new stem seals. I am assuming all stem seals are created more or less equal. Mine were from a top end gasket set from eBay.

1 to me seems most likekly and as many of you have said i do need to run it in. I can only trust that the rebore was good. The guys who did it are a large concern and do rebored on every thing from automobile exotica to aero and truck engines. I have used them before with no issues. They assessed the engine and supplied the pistons (county brand). The bores are nicely crosshatched. I fitted the rings to the pistons and am sure that the compression rings are the correct way round. The oil control rings where the 3 part types and they seemed to go in ok. Two scraper rings did not have any up or down written on the which I was not surprised about as they are thin and would not be asymmetrically shaped. I checked the rong gaps and they looked pretty much spot on. The pistons also went in fine. Regarding running in. So far it has been a bit non ideal.
First start up had issues with smoke (loads of it) and the car was shut down after 3 mins or so running at idle. It was run once more for a similar amount of time to check the breather issue. The engine was started a second time this time with the breather issue solved ( or so i thought ) and left to idle at until warm. It ran rough until I realised that 2 of the spark plug leads were crossed. Than ran beautifully.
Finally it was run for another 5 mins with the new head. For some of the time the revs were raised to 2 k. Now I know this is not ideal. I had planned, 5 mins to temp. Re-Tighten head. Then run at 2k for 20 mins. Whatever the problem if it is piston related it is going to be more work than just seeing if it needs running in!

I think I will put the head back on and do the 2000 for 20 mins and then leave alone until I can take it for mot. Then see what happens?
Cheers
Tim

Cheers
Tim
T Dafforn

Guy, we crossed posted again. The rocker is the only part of the engine with unknown provenance. It came in a bundle of parts which came with the car. I assumed is was new as it was in a plastic bag and looked clean. Hmmmm I wonder. How do you check wear?
Tim
T Dafforn

A worn rocker shaft will show scoring and ridges where the rocker bushes run. Always worst on the shaft underside because of the upwards pressure from valves, pushrods and springs. Wear in rockers is evident by them feeling slack/ loose on the shaft but this won't show up whilst the rocker assembly is bolted down because of the spring pressure.

Tim, I am not saying that these ideas are absolutely the problem! Just following a train of thought and saying what I would be checking. I may of course be on completely the wrong track!

From your last post I gather the engine has had very little total running time, and almost none, if any at all, at a proper running temperature. As regards the oil smoke it could well just need a proper bedding in procedure to cure the smoking so it could be you are chasing an unimportant issue at this moment. My earlier comments still apply regarding oil retained by the cross hatching of the bores and not being removed by the oil control rings as they haven't bedded in yet.

The running at 2000 rpm for 20 minutes is critical in bedding in a new camshaft. If a new cam is run at low revs the cam lobes apparently wear rapidly so that 2000rpm running needs to be done very early on in the sequence - just as soon as the engine can be got stable enough. I would say this is much more important than chasing a bit of blue smoke in the exhaust.


Guy W

Tim, were any of your rings "cup" rings. And if so did you fit them the correct way?
Lawrence Slater

Addendum - Did you check that the rocker shaft has its screw-in end plugs fitted?
Guy W

Hi Guy,
Will check rockers...
Agree about the cam break in..
Lawrence, not sure what you mean by cup rings? compression rings were fitted with the correct side up.
oil control rings didn't seem to have any indication of a specific orientation. There were the ones with two scrapers separated by a corrugated spacer ring.
Cheers
Tim
T Dafforn

Hi Tim. Picked up this thread now after your reply to mine. You are getting a lot of advice from knowledgeable people, some of it scary, but for what it's worth did you use a copper or composite gasket? When I first put mine back together I was advised to use the modern composite. It leaked. Another chap said that the a series would not put enough pressure on a composite and to use a copper one. I did this and it was OK.
I know how you feel and the idea of a fire sometimes seems like a good one
Walter
W Clough

Checked rocker. Has plugs not grub screw in each end. Where these the screws you were talking about. The rocker gear is also unworn. Compared with another I have that came off a running engine and the rockers have a lot less ( virtually none) play one the shaft.
Still can't work out why there is oil in the inlets? O well
Plan.
Rebuild
Check compression
Run in at 2000 rpm for 20 mins
Change oil and filter
Leave it alone until mot
Tim
T Dafforn

Tim

What source did you use for ring gap spec.

Haynes manual - or - the piston manufacture parts box / website

With the head off, id pull a piston that looks most suspect for a looksy.....its an extra 1/2 hour and $10 to have the big end of the connecting rod re-trued to round, and a pan gasket

Imho....it just seems like your getting way more oil then what would be normal for a new engine break in

Prop
Prop and the Blackhole Midget

Photo of what happens if you use the haynes manual for ring gap spec....

Yepp...JB weld wont fix that. LOL

http://db.tt/mpYc8Af1

Prop

Prop and the Blackhole Midget

Nice. What brand of piston?
Tim
T Dafforn

Possibly some progress.
Refitted the head. Risked reusing the head gasket.
Then did the 20 mins at 2000 rpm run.
Had to stop at 5 mins to let things cool a little ast the electi fan had come adrift. Then ran fine.
Result still some smoke at 2000 rpm, but none at idle.
Blowby from the crankcase breather seems pretty minimal.
Will retighten the head and then try the compression tester.
I did notice that the smoke at 2000 rpm seemed episodic at times. Certainly no smoke at 2000 on restart even though the engine was hot and for one section of 5 mins virtually smoke although there was quite a breeze running through the garage at this point!
Also drove the car into the car park to turn it round.
Counted as my first ever drive in a midget.
Cheers
Tim
T Dafforn

That piston was an AE version made in japan...I cant think of the name now, it was considard a good name

Congrats...hopfully it just needs breaking In.

Sorry to have freaked you out


Prop
Prop and the Blackhole Midget

Not sure I'm out of the woods yet, but perhaps there is a light at the end of the tunnel (too many metaphors induced by too much wine!)
Cheers
Tim
T Dafforn

"Refitted the head. Risked reusing the head gasket."

I'm afraid you'll quite possibly come to regret that. If you don't pull the head and replace it, then make sure you retighten it after "some" miles. However, be careful not to overtighten it. The hg has already been compressed once, and if you over-compress it, it'll stop sealing at the fire rings. This has been discussed a few times recently.
Lawrence Slater

Hi Lawrence
Absolutely agree, will replace (didn't have a decent spare at the time) before I run it next. Getting quite slick, should be able to do it in under an hour.
Cheers
Tim
T Dafforn

Yeah you can get quite good at it. I did my hg once by the side of the road in France, circa 1978/79. I broke a stud when I built the engine and was torquing the head. As I was able to extract the stud, I thought I'd get away with it, and I did for about a thou or so miles. Then later that year me and a mate drove to Spain and Morocco in my Sprite. Somewhere down south in France, it started overheating and burning a lot of oil. I knew it might be a problem so I took a spare hg with me. Just as well. lol



Lawrence Slater

Impressive !
Have to say that doing the head gasket on the mg is easier than on the lotus I used to have!
Mind you that didn't produce smoke when in rebuilt it!
Cheers
Tim
T Dafforn

Update.
Looks like the issue is with the way I fitted the spacer for the oil control rings. Fitted it with an overlap rather than butted
Wasn't helped by a lack of instructions with the pistons.
Will refit and see how it goes
Cheers
Tim
T Dafforn

Hi chaps
Well, started the engine after fitting the oil control ring separator with the ends butted.
Result.
Smoke free engine.
Vvvvvvv happy camper :-)

Tim
PS Prop, recommend fitting the rings butted
T Dafforn

Hi Tim
Good news! Where in Warwickshire are you? I am in Warwick, would love to see the car if you are passing.
Carl
C Bintcliffe

Hi Carl
I'm in kenilworth. The car is not MOT 'd yet but hope to get that sorted by the end of the month. It'll be the first time since 2007 and the first time since I bought the car as a basket case. Just need a number plate and a new V5. Happy to meet.
Cheers
Tim
T Dafforn

Hi Tim

One quick query. You say that you refitted the oil control rings. As that must involve removing the pistons, is that possible with the engine in situ or did you have to take the engine out to do that? I presume your engine is a 1275 A series and not a 1500 or have I misunderstood.

Chris
Chris H (1970 Midget 1275)

Wow! Im Impressed... Prop got you threw that? You were able to take the pistons out rearrange the oil rings put it back together and no more smoke.

I think I may have lived with it alot longer before coming up with an answer unless it was on my mind before hand. Still pretty amazing you were able to solve that so quick. Goodluck!
Steven Devine

Not too bad a job really..
30 mins to get the head off
car up on ramps
1 hour to get the sump off, big ends, pop the pistons, refit the rings.
1 hour to refit pistons and sump,
20 mins to take the sump off again to check the big ends where bolted down the to correct torque (paranoia!)
10 mins to refit sump
30 mins to put the head back on..
3:30 total
(Engine is a 1275)

Cheers
Tim
T Dafforn

This thread was discussed between 04/09/2013 and 11/10/2013

MG Midget and Sprite Technical index

This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.