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MG Midget and Sprite Technical - 1275 exhaust problem on Frogeye

I've been trying to fit a s/h single box standard exhaust from a 1275 (but same as 1098 I believe) on the 1275 Frogeye. The front pipe is fine - aligns quite well although I had to grind a bit off the footwell front lower flange. When I came to fit the silencer I found the rear of the front pipe doesn't sweep up enough such that the silencer bracket is too low in its "natural" position i.e. maybe 5/7cm below the boot floor stud it attaches to. It also sits inboard of the stud and projects too far at the rear. Is this normal? Do I need to be a bit rougher and force it? The problem then would be it binding on the axle when jacking car up with axle straps at full stretch. What to do?



Bill Bretherton

Bill, do you have the two part exhaust pipe, or is it one single length between the bottom of the manifold and the silencer?

Mine came in two sections and by rotating them I got the alignment to work. From your photo it looks like the rear end of the pipe needs to rotate so that it dips under the axle, and then rises up to the correct level for the silencer.
GuyW

I had this problem when I had a stainless steel pipe made. I ended up in having the pipe rebent so it would clear the axle and allowed the silender to fit on the stud. The problem is the standard 1275 pipe is bent differently to the frogeye one. The frogeye one is kinked at the end so the silencer exhaust pipe exits to the left of the rear bumperette and actually points slightly to the nearside. It does not come out straight. The early 1275 silencer has a longer exhaust pipe and exits more to the right. What I have seen is it that the rear silencer is allowed to 'hang' lower so it clears the axle. the bracket on the silencer is extended to allow for this. The aftermarket exhaust made by Maniflow and the like also fit but exhaust to the right of the nearside bumperette.
Bob Beaumont

Guy, it's a single front pipe so no adjustment.

Bob,thanks. So I do have a problem! Looks like it needs major persuasion.....
Bill Bretherton

How about using a longer bolt to attach the silencer? Just an idea.
Martin

Martin, I might do that but want to get the silencer as high as possible.
Bill Bretherton

Bill,

Having mulled it over night, I have a question, are you using the mounting bracket that holds the center of the exhaust pipe to the rear bulkhead? If so, that would give you the proper height of the pipe at the rear of the car which means that you would probably get some interference with the rear axle. If you lift the axle things should line up but that means that the check straps is useless on that side since the exhaust pipe will stop the axle before the strap does. At least that is how it works on my car.
Martin

Some check straps are shorter than others. Do you have the correct shorter ones?
GuyW

Since my old ones were pretty rotten I got the ones sold by Moss but I have thought about making my own. But since I don't know how long to make them (too lazy to do the math right now) I haven't done anything about it.
Martin

Martin
Yes, I'm using the rear bulkhead mounting bracket so the exhaust should be in the correct vertical and horizontal position. As Bob said, the original Frogeye exhaust was different such that it exits left of the nearside (USA driver's side) bumperette. I think I'll make an extension bracket to attach the silencer to the stud and cut a bit off the projecting tail pipe. I presume a lot of people with 1275 Frogeyes have an LCB so that the cut front pipe can be rotated to orientate the silencer. I can't do that.

However I note in Moss catalogue that the 1098 exhaust is the same as the 1275 (single box) so there would be similar problems with a 1098 engine as you need a later exhaust. Never straightforward is it!
Bill Bretherton

"Never straightforward is it!"

No, it's not.
Martin

your correct Bill

The 1098/1275 exhaust pipe is the same. Its after the middle bulkhead mounting the problem arises. I remember now I had this problem with a 1098 engined frog I used for production car trials.The rear springs had been retempered to give a higher ride height and the exhaust was close to the axle. I fitted the silencer to the right of the bumperette with an extended cotton reel mounting. The silencer tail pipe was also shortened to finish just after the rear panel.
Bob Beaumont

Bill. I bought a new 1098/1275 pipe for mine. When it came it was in 2 sections, I presumed for ease of postage. The front cannot rotate as you say because it needs to connect up to a standard manifold. But the rear half is joined with a clamp ahead of the rear bulkhead mounting point, and can be rotated. It has a slight downward bend, followed behind the axle with a more pronounced bend.

It took a bit of experimenting but by rotating the rear part one can get a balance between dipping under the axle with enough clearance, and alignment to the silencer bolted up to the boot floor with its standard bracket. It exits to the right of the bumperette, not strictly correct for a frog but looks ok.

Maybe you could cut yours and remake the connection with a sleeve?






GuyW

Bob, Guy, thanks.

So I defintely need to shorten the tailpipe. I had thought about cutting the front pipe but it introduces another potential leakage point! But I may still do that. Interestingly the Frogeye is 12mm LONGER than the later cars so that extra length must surely be in front of the engine or the later exhaust wouldn't be longer at the back.
Bill Bretherton

CORRECTION:
I think my length comparison is incorrect plus I wasn't allowing for rear bumper on later cars.
Bill Bretherton

Bill, the boot floor is the same (or at least I used a 1275 boot floor panel and it fitted) Perhaps the overall length includes front bumper which I think is set further forward from the front "dumb irons" than the front bumpers of later models.

If you do decide to cut it, the easy connection is to find a close fitting sleeve piece, IntD the same or only very slightly larger than the OD of the existing pipe.
GuyW

I fitted a frogeye boot floor panel into a 1500 as Moss Bristol didn't have the 1500 panel in stock, a perfect fit. I think the difference is in the spare tyre retention with the frogeye having hoops fixed to the floor and the 1500 having a thread fixing IIRC.
David Billington

The problem you have is that a 1098/1275 exhaust is for 1/2 elliptic sping axles but a Frogeye of course is 1/4 elliptical.
I had this very problem fitting a 1275 Maniflow exhaust to a Frogeye. It just doesn't fit despite Maniflow saying otherwise ("we've never had any problems").
The 2 piece pipe joins just after the rear bulkhead. The part that joins to the box bends towards the nearside wheel then has an S bend into the silencer. The problem with this (in my case at least) is that on the Frogeye this pipe contacts the bracket on the axle for the shock down link. To clear this you have to rotate the pipe slightly, which causes the S bend to lower the silencer. I could find no happy medium so I had to hammer the crap out of the pipe to make it go straight back, just as the Frogeye exhaust system is supposed to do.
Rob
MG Moneypit

I'm surprised there isn't more in the Archive as this must be a common problem. Perhaps we're all suffering in silence(r)!
Bill Bretherton

Rob, when I first tried mine,like yours, whichever way I rotated the rear section of the pipe, it either contacted the bracket on the axle, or wouldn't align with the silencer.

I then reversed the pipe clamp that bolts up to the rubber mounted bush on the rear bulkhead. This moves the pipe over to one side by about an inch. This doesn't seem much but the amount is magnified further back so I could then get an alignment that comfortably clears the axle bracket. It worked for me.
GuyW

Just wondering - the 1098 mk2 Sprite/ mk1 midget use the later exhaust according to Moss. These models have quarter elliptic rear springs so you'd think they'd need a Frogeye shape exhaust but suitable for a 1098 engine. But there are only two single box exhaust types.
Bill Bretherton

Good point, but I think the 1098 Mk1 midget had a different exhaust manifold to the later 1098 Mk11 midget( which was the same as the 1275). I bet it used the frogeye system and Moss have just got it wrong. The morris minor had the same exhaust system regardless of engine size.
Bob Beaumont

I thought the later 1098 exhausts were just a larger diameter than the original Frogeye ones? But the alignment at the rear will have changed with the switch from 1/4 to 1/2 eliptic springs. The early pipe exits to the left of the bumperette, but if you fit a later system designed for the 1/2 eliptic cars the pipe ends up exiting to the right of the bumperette. It was moved across to clear the rear part of the spring and the rear shackle. Apart from that I don't understand why the pipe route for a 1/2 eliptic car won't work on a Frogeye. The axle, though hung differently, is in the same relative position as regards routing the pipe underneath it and although it must clear the suspension mounting bracket on the axle, this is in much the same position as the spring pad and rebound turret on the later axles.

Mine certainly fitted ok, that is using a 1098 engine and standard CI manifold linked to a 1098/1275 middle 2-part pipe and silencer box.
GuyW

The problem with mine is when the car is jacked up on the exhaust side so that the axle is at maximum stretch on the strap and is tilted down on that side, so it's an extreme case I suppose. With the pipe touching the axle the silencer is too low. However I haven't fully tightened the suspension yet and it could be that I can get it close enough. Probably next week now, will report back.
Bill Bretherton

On 1/2 elliptic cars the shock absorber downlink is attached to the spring pad, the downlink being U shaped. On 1/4 elliptic cars the downlink is attached to a bracket well away from the spring attachment point and the downlink is Z shaped. The bracket on the axle on 1/4 elliptic cars is 3 to 4 cm closer to the exhaust pipe which is why I had trouble fitting the Maniflow exhaust for a 1275 to my Frogeye which has a 1275 engine fitted.
Rob
MG Moneypit

Effectively the 1275 pipe needs to be broadly the same shape and curve as the 948 one!!
Bob Beaumont

I've got a Moss GT system on my Mk1 which is for a later 1275. It fits nicely BUT it is one for an LCB so you can rotate the main pipe until it fits. It doesn't have the small bends for the axle, just two small parallel bends about 18inches apart. It leaves the rear box angled down at the front but that means it sits nicely at the back - but only if a bumper is fitted, it would look a bit low on a bumper less car. The only problem I've had with it that I was suffering from fumes being sucked back when the top was down, solved by fitting a downwards angled SS exhaust trim.
John Payne

John has put something that was in my mind when there was talk of cutting the tailpipe. Previously a fellow Spridgeteer reported carbon monoxide from his vehicle (from headrest IIRC) and even for those who are too macho to worry about such things as possibly being poisoned still are macho enough to worry about appearances, cosmetics and the like so might worry about staining to the rear of the car.
Nigel Atkins

Nigel
As I understand it, the tailpipe shouldn't project further back than the most rearward part of the body/ bumper so may have to be cut anyway.
Bill Bretherton

Yes, I cut mine so it was just level with the edge of the bumper, just to the inner edge of the overrider.

As soon as you got above 40mph you could smell the fumes which obviously isn't good. A bit of searching the archives and someone recommended an angled trim which works perfectly. Only problem is it looks a bit naff but better than being poisoned!!
John Payne

Before:




John Payne

After:



John Payne

Bill, unfortunately my car is all wrapped up for winter or I'd try and get some decent photos of the exhaust fit for you.
John Payne

John,
probably me that recommended the naff tailpipe trim, there used to be a choice of them when I was much younger and they looked posh as they were chromed rather than rusty broken metal black as the tailpipes could be.

Bill,
I'd leave it longer, at least as far as the outer edge of the bumperette, you can always cut it later. Mine is about 1"+ out than the outer edge of the rubber on the overrider, and it's on a slant.

Who know if you get more, less or the same blowback from the Frogeye boot shape.
Nigel Atkins

Thanks John. Nigel, I won't cut it yet - will wait until the bumperettes are on sometime next year. Easy to remove material but more difficult to put it back. DAMHIKT!
Bill Bretherton

Well it's on. I've made a "dogleg" bracket to allow the silencer to hang more inboard than a Frogeye one. It is correct fore and aft. Also, with the car jacked under the rear spring hanger I had to drop the silencer 2 inches so that the axle casing was just touching the exhaust. I have Moss springs and the car sits high so I assume the axle is dropping more than normal with body jacked up - check strap at full stretch. When the car is on the road and "settles" it could be I can adjust the silencer upwards. But it will do for now. Garage cold as hell today!

Thanks for all the help and suggestions - really appreciated.



Bill Bretherton

IF I ever get aroundtuit I'm going to have a very short hanging bracket (if a unf cup hook isn't available) and if I can get one small enough, use a small modern pig's nose rubber fitting.
Nigel Atkins

Being high on the suspension shouldn't make any difference to the exhaust clearance on maximum "hop" as this is limited by the check straps. That's assuming you have the correct length (shorter) Frog check straps. If it stands high on the suspension to start with then there is just less movement available before the check straps stops the axle dropping further.
GuyW

Guy
The check straps are Moss rubber ones - only one length available. Same part no. for semi elliptic.
Bill Bretherton

There are definately two lengths. Though maybe the difference is between 1500 and then all earlier models.

Point still remains, How far the axle drops is dependant on the length of those straps and is not related to the ride hight. Its just that if the ride hight is high, then the available "slack" in the strap is less, that is all.
GuyW

You're right so it must be that my exhaust doesn't sweep up enough behind the axle. I got it with other used parts from a local Midget owner and don't know its vintage.
Bill Bretherton

Part number change for those straps is for the 1500. They must be the longer variety so unless you were sent the wrong ones that won't be the problem.
GuyW

I originally bought the rubber straps from Moss, and a year later when I came to fit the Maniflow exhaust I found they were too long to fit the exhaust.

I ended up measuring what I needed and found some on eBay.

The rubber straps had been used for a year, so im not sure if they were too long in the first place or had stretched whilst the car was on stands in the garage.

I'm not sure my comment is particularly helpful :-/
Chris Madge

Some dimensions from my Frog Bill so you can lay this particular cause to rest.

Strap length, eye to eye is 22cms. My car is still a little high on it's suspension so direct line between the two fixing eyes with the car on its wheels is 18cms. So there is around 4cms of droop available.

Current clearance to the pipe is 7cms so I have about 3cms in hand. Possibly a little less, depending on how much stretch there is in the straps. Mine are laminated with a reinforcing webbing so I think are not supposed to stretch much if at all.
GuyW

Guy,
Not been keeping up with this thread but that is a shiny silencer on your Frog !!!
Assume you have ejected the very dangerous Somerset spiders !

R.
richard b

Richard, I thought I would leave the rare Somerset spiders as they will ward off the midges when we go up to Scotland next spring.
GuyW

Thanks Guy. Have just measured mine quickly - strap length is 25cm eye to eye (one side jacked up only with strap at full stretch). On wheels strap is 20cm eye to eye (so car sits 2cm higher than yours). Clearance top of pipe to bottom of axle case, car on wheels, is 5cm. When jacked up, exhaust almost touching axle. Rubber straps, so they stretch - yours sound better, my axle would clear the exhaust by 3cm at full droop. However, my silencer bracket is still about 4/5cm below boot floor so the upsweep on the pipe behind the axle is less than it should be.

Bill Bretherton

Unless I misunderstand those measurements, it doesn't sound like the straps are stretching. Just they are slightly longer to start with.
Your strap is 25. Mine is 22. This when not under tension.
My available slack in the strap when on its wheels is 22-18 =4cms
Yours is 25-20 = 5cms

Clearance under axle to pipe on mine is 7 CMS so if strap doesn't stretch that still gives me 3cms safety margin.

Yours appears to be 5 CMS under axle and you have 5cms slack available, which is why your pipe is contacting the axle, with no safety margin. If you had 22cm straps you would have a 3cm safety margin.

Where did you get the straps?
GuyW

Guy, the straps are from Moss, correct part no. in their catalogue. Agreed, shorter straps would be better. Where did you get yours?
Bill Bretherton

They came with the car. They are still in good condition. I don't know if they are original, or replaced at some stage. But if they were that would have been pre 1984 unless the PO who started out on the rebuild bought them as second hand as although they are OK, they are not unused.
GuyW

Shorter straps might simplify the exhaust clearance problem. But that doesn't necessarily make them better. If straps were too short they would result in more frequent rear wheel lifting, presumably at lower speeds.
GuyW

So should one expect a Sprite rear axle to occasionally drop to the limit of the straps with "normal" driving?
Bill Bretherton

For what it's worth, my original straps were some kind of woven material. Since, when I replaced them about a year or so ago, they were grimy and falling apart I'm not sure what they were made of but they were original and not rubber. I'm not too sure about the current Moss replacements since they look as they might stretch and break with time, so I've been thinking about getting some woven nylon cord like that used for tow ropes and making my own as someone here (can't remember who) did a few years ago.
Martin

Its not the axle dropping. Its the body (and exhaust with it) lifting as a result of body roll. Corner fast and body roll will lift the inside rear corner of the car. When the strap pulls tight it will start to lift the axle and the rear inside wheel lifts.

How often this happens on the road will depend on how much you push it on the corners. With a reasonably low C of G you need to be going pretty hard to get to that stage.
GuyW

Yes, I guess that's obvious thinking (!) about it. I've kept wondering how strong the Moss rubber straps are against the weight of the axle in the event of body roll or even when jacking the car up by its body.
Bill Bretherton

This thread was discussed between 02/12/2020 and 08/12/2020

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