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MG Midget and Sprite Technical - Is this normal?

Endoscope received as a present. First job was to check out no 1 cylinder.
Is the scoring normal or do I need to worry?
Not done a compression check yet and it uses very little oil, rarely needing a top up between annual services less than 2k miles in the last couple of years.




Jeremy MkIII

At first sight it looks okay to me Jeremy. Perhaps a little more pronounced looking than I might expect, but that might be down to your endoscope being better than mine.
It looks like normal crosshatching from a glazebreaker to me.
If there were heavy vertical scratches on the borewall I'd be worried but I don't see anything like that.
Willy is much more experienced with this - I'd be interested to know what he thinks.
Greybeard

Cheers Grey, thanks for that. At lease there are no vertical grooves as you describe.

The endoscope was a £20 ebay Chinese make with an app downloaded from the App store so they probably have a copy of all my contacts and email addresses by now!
Jeremy MkIII

I'm with Grey on this. Looks like normal (what we on this side of the pond call) honing marks. That tells me that the engine doesn't have many miles on it. As long as there are no vertical marks, I wouldn't worry.

And soon you will be getting E-mails and text messages trying to get you to buy a whole list of automotive related things.
Martin

Ha ha ha--nice little chinese man have set of pistons to suit car for sale at new friend's discount price to regular customer who buy camera---lol

Yeah ,I'd agree with Grey.
Typical crosshatch pattern, probably done with a fairly course stone taking the pic at face value---but the pic is probably fairly magnified with the light showing the scoring marks deeper than they actually are.
When you look at the pic on the screen you have to judge the bore size, On my screen it's about a 2foot bore so approx.8X magnification so the scratches reduced by 8X will hardly be visible

Good little camera you've got yourself there, I paid way more than that for mine and the pic isn't any better than yours---good toy, poke it in your partner's handbag for a look, it's interesting what they keep in there.
William Revit

>>poke it in your partner's handbag<<

You like to live dangerously, don't you Willy?
Martin

Do you have the ebay link/item number Jeremey?

I've been meaning to get one of those too.

There ate so many for sale, and to know that one makes such sharp pictures is very useful.

Yep looks normal to me too, but your big additional clues are, hardly using any oil, and presumably running well.
anamnesis

Damn, those of us with rebuilt engines all now need to buy an endoscope 😉
Bill Bretherton

😅😅
anamnesis

Haha Martin! Super discounts from my newly acquired Chinese friends are on their way. The engine's done about 10k so well surmised.

Not that brave Willy but thanks for the reassurance that it's normal wear and tear.

Anam, that confirms my thinking, thanks. I don't have a direct link as my son bought it for me.
This though is the same model (and I think where he got it from)
https://tinyurl.com/5n94tnxb

I went for 1200p with a 2m cable with wifi as my phone doesn't support USB. If yours does or you want to use it with a laptop then USB versions are about 1/3 of the price but seem to only come with a 1m cable?

It comes with a few attachments such as a mirror, hook and magnet and are supposedly waterproof - don't intend to test it!


Jeremy MkIII

I went for a USB version with a 5m cable initially which was a mistake. It was cheap enough but the cable was a PITA. Way longer than I needed.
I sort of solved the problem by putting it down the injector hole on a CAT diesel. It went in fine but wouldn't come back out and I broke it trying.
Humble pie for tea...
But before it died it showed us horrendous scoring in the bore and what turned out to be bits of the rings embedded in the piston crown so the engine had to come apart anyway. Luckily the CAT is a wet liner engine which was just about doable in situ.
The new scope has only a metre of electronic string which has been okay so far.
BTW it was less than a tenner delivered!

I wouldn't risk it in Mrs GBs swag either!
Greybeard

The best use I found for my very cheap endoscope was finding a wasp nest underneath the garden decking.
Les Rose

Thanks Jeremy, I'll check those out.
anamnesis

You're welcome Anam, hope you find one. They're the sort of tool where you look to find other uses for it.
Maybe we should see who can come up with the strangest use? Willy's winning so far :)
Jeremy MkIII

As my engine as recently been rebored and awaiting reassembly thought I’d take a photo of the machining that a local classic engineering company did.

Not sure if it gives you comfort or not with the work you’ve had done.

James Paul

Jeremy,

I are sure the scope is waterproof. I lost my BMW car key in the Water Closet while flushing but i could locate the key with the scope! BMW can replace the key for €420...

Flip
Flip Brühl

Paul that is reassuring, looks very similar, thanks for posting and hope the reassembly goes well.

Haha Flip, glad you retrieved your keys. What a way to test the waterproofing!
Jeremy MkIII

Just an outside observation with no hidden meaning or agenda--
When I first saw Jeremy's pic of his bore I thought, gosh that's had a course old hone job, normally you'd expect hone marks to virtually disappear after a few thousand Klms
Then when James put his pic up of his newly honed bore, then I realised your engine reco guys there are behind the times a bit-
Don't get me wrong both your engines will be fine--
Here now if I went to pick up a block at the machine shop and it had a course hone like that I'd be peed off.
Nothing you can do about it now as it's been honed to size, it'll be ok ,don't worry but it's a bit old school by todays standards
Ring technology has changed quite a bit and most, if not all quality ring sets are now prelapped to bore size meaning you don't need angry honing for running in and the bores to suit them are what is known as plateau honed which is done by a set size fine hone at low pressure which cleans up all the fine,jagged edges in the bore that the rings used to be expected to do
It's done by only 8-10 swipes down the bore with the fine hone
To get pedantic about it I used to do the plateau hone in the opposite rotational direction when I'm after something special which creates a bit of an issue as my local guy's bore/hone machine spins in one direction only---so it's back to the old manually operated hone which usually ends up with ,it's over there in the corner mate, go for it
Couple of pics---nicked from the net for demo.
#1-Normal hone probably 180 grit then should have a 240 grip chase up
#2- Plateau hone 240-320 grit in reverse direction--NOTE --Prelapped or moly insert rings are used for this finish

willy





William Revit

That's interesting Willy.
So because of improvements in piston ring technology you can have a much smoother bore which presumably offers less friction and therefore better performance. Or is that over stating the case?
Jeremy MkIII

And to add to Jeremey's question, does that mean no running in period anymore? Pre-runin?
anamnesis

Both correct-
Less early run in friction
After run-in the friction /performance should be same for both though, just a different way of getting there-
The advantage of the pre-lapped rings in a smoother bore is that there is virtually no runin period needed which suits new car manufacturers as they don't have to rely on buyers doing the right thing-
On a full on race engine you'd plateau hone with 360 or even 400 grit if you were going onto full power straight up
The trap is that if you use a non lapped in ring set in the smooth bore it'll take forever if ever to run in and seal up properly ,specially if it's a non lapped chrome ringset
Hope I've explained---
willy
William Revit

I always believed - and probably too simplisticly, that the cross hatch honing was to help retain an oil film on the bore and it was this film that helped create the pressure seal with the ring. If this is in any way correct perhaps the finer and improved oils work well without this "assist". Or at least with a much finer hone pattern.
GuyW

This is the sort of thing that these BBS topics are so good for. We can all tighten a screw, bolt bits together and even follow a set of written instructions. Even checking with Nigel's good book when necessary.

What is so much harder is the judgement thing, based on experience. Things like looking at those marks on the bore and knowing where that stands on a spectrum of possibilities from perfect to bu66ered. Or the feel of a bearing as you spin it in your hands - Is that amount of free movement acceptable? Then along comes Willy (and a few select others) with helpful advice and opinion based on practical first hand experience, good judgement and the engineering explanation to back it up.

It's just brilliant!
GuyW

Guy-I'm happy you're happy,I really enjoy this sort of talk-
You are spot on with your understanding of the crosshatch holding lubricating and cooling oil for the rings during the runin period along with having a surface that can bed in a bit as the rings/bore get used to each other
Even with the finer finished bores it's important to keep the hone angle correct at 30-45 degrees inclusive--that is 15-22 degrees angle from horizontal
Any flatter and the oil can't get dragged up/down the bore to lubricate and scrape back properly and can cause the ring surface to scuff up, and on the other hand if the honing is too steep oil can get pumped up the grooves and cause oil burning and also can cause the rings to spin in the piston grooves causing oil pumping and ring groove wear as they follow the honing grooves in a spiral
For some reason when the honing is at the correct angle, the crosshatch holds oil but doesn't cause pumping
To me the flatter 30(15) deg. honing just looks the business

willy
William Revit

Amazing this type of honing subject, and ring type, hasn't been discussed before on here.

Willy, pre-lapped rings. Does that mean we should make sure to get those first as a prerequisite to also asking for plataue honing insted of coarse honing? Or are all piston rings these days made pre-lapped, and can be used in the coarse hatch finish too?
anamnesis

Opened a can of worms here--this could go on for a while i thinks-

Me, personally, yes, I always go for plateau honing, but ring choice is important, specially if it's a road car and near zero oil consumption is expected-
With the finely finished bore it's important to only give it the 8-10 swipes with the hone otherwise it will be too smooth and won't hold any oil for breakin, even with prelapped rings there needs to be some visible hone marking---The choices are ,prelapped ,or a ringset with moly/plasma inserts which are designed to bed in quickly to a smooth bore although these are known for taking quite a while to finally completely bed in and can use a little oil in the meantime
You can identify the prelapped sets by the look of them on the bore contact surface, they'll be that light grey colour there and semi dull texture, easy to see if they're a black cast set with their grey edge and the chrome sets will be shiney chrome with a dull grey edge.

With the courser honed bore you can run either prelapped or not, the bore finish will do the lapping job as has been done for years and will be for years to come probably-with prelapped it'll bed in quicker

The main advantage of the plateau hone method is as we mentioned earlier --early break in, meaning new engines can get onto full power early on in their lives

I look at it a bit differently, my view of it is just say for example you want to build an engine with for example 3" bore and normal cast pistons so it'd have probably .0015" clearance and .006"-.008" ring end gap
With the course bore finish you'd need to go probably .001" clearance and the lower .006" gap so that after run in it's out to the .0015" and probably around .007-8" gap
You'd have to make sure it's not overloaded during runin otherwise it could scuff up the pistons and rings from being too tight
With the smoother bore and prelapped rings everything can be set to specs and they won't change at all during/after runin
On your question of are all ring sets prelapped- NO
It was getting towards being that way here a few years back but now with ringsets coming from who knows where , India, china , turkey there's a flood of non lapped and unfortunately it's becoming the norm. But there are good sets out there
I guess that's the main reason the average engine reco place goes for the courser bore finish-to cover their backs against ring choices ----If they did them all micro finished and someone poked a set of non lapped chrome rings in there they'd probably never bed in and they'd have unhappy customers
It's all a matter of choice----
willy
William Revit

Thanks Willy. That's what I call a comprehensive answer.

I wonder if machine shops here all understand that as well as they should. Might be worth asking the shop about it to see if they do, before letting them do the job. And with your explanation, we'll have a better idea of exactly what to be asking them too.

I've got a bit of piston slap (which is getting worse) in my 30 thou over 1275. It still has great compression, runs well and doesn't burn excess oil, but it's done at least 180000 miles on those bores and pistons, -- been re'ringed. So I've been considering a rebore, and this subject has come up at just the right time for me too. -- Although I don't do that many miles per year now, so it'll probably do a good many years before it causes any problem.

It all 'seemed' so simple back in the '70s. 😄.

anamnesis

This is fascinating and an education although I'm only on the edge of understanding it! I'd assumed that modern cars need less or no running in because of more accurate CNC machining and that older blocks e.g. A series could never be machined as accurately so that the pistons (or rings) in a newly rebuilt engine were "fighting" the bores a bit more so took a while to bed in.
Bill Bretherton

I'd reckon they know all about what's good and what's economical for them- There'd be plenty of good machine shops in the UK i'd think
The thing is though, for a car enthusiast doing his own engine, if he's loaded up with info he can ask the right questions instead of just dropping his bits off and getting back whatever he's given.
In the big scheme of things the extra cost for a good job is virtually nothing compared to the total cost of the job
Don't get me wrong, I'm not knocking the courser hone job, it has been ,and still is the norm for most domestic work and does the job just fine.
Just letting you know there are other options -
Cheers
willy
William Revit

This thread was discussed between 24/06/2022 and 30/06/2022

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