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MG Midget and Sprite Technical Head basket (again). BBS discussion at MG-Cars.info
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MG Midget and Sprite Technical - Head basket (again).
| My 1133cc (1098+40) Sprite has just blown its 4th head gasket since I rebuilt it in 2008. This last one lasted about 6000 miles. It was a competition item bought from Moss. I have uprated studs, nuts and washers fitted. It has previously blown between 3&4 and last time between 1&2. I’ve not taken the head off yet so I don’t know where it’s blown this time. No coolant issues, so I guess again it is between two cylinders.
So, a couple of questions. What is the best gasket to buy? (I’ve heard that Payen have had problems with leaks) Do I need to have the head and block surfaced, and if so do I need to buy new pistons? |
| b higginson |
| This is exactly the problem with which I struggled for years. Repeatedly skimming the head did not fix it, only decking the block did. You are faced with an engine strip down, machining, and rebuild. If your pistons and bores have only minimal mileage you might get away with keeping them as is. I tried many brands of gasket and nothing worked. Only skimming both faces did. |
| Les Rose |
| I’m wondering if the block is flexing. The 1275 blocks eventually got a thicker flange to stiffen them up, but my ‘65 block has the tappet chest which might make it more prone to flexing. Bernie. |
| b higginson |
| I'm no expert on big bore blocks, but from what little I have read the factory was always trying to reduce vibration. Hence the A+ block had lots of stiffening ribs. I don't think I've seen anything about flexing. On my small bore block the problem was distortion of the top deck, which could only be cured by machining.
I suggest that first of all you whip the head off and get it machined. The first time I did this the machinist found a warp of 0.004". That is more likely the problem than the block, but if it doesn't work then you're in for a rebuild. These engines of whatever size seem to run hot in the centre. I always see signs of heat staining in that area when I take a cylinder head off. I suspect the siamesed exhaust ports are part of the problem, and this is likely to be worse with the 1275 because the water passage between the centre cylinders was eliminated. But as I have found, the small bore blocks can be little better in this regard. We have to remember that these castings are well over half a century old now, and use and abuse are likely to have distorted some of them. Just a thought: you say you have blown 4 gaskets in 15 years. Are these failures clustered towards the end of that period? If they are evenly spaced then you will have to wait about 5 years for the next one. If you have had say two failures in the last year then you need to do something about it. |
| Les Rose |
| When I had my1098 rebored the company who did it said +20 was the maximum they could go. Would going to +40 but too much stress on the gasket like you are experiencing? Mostly curious. |
| James Paul |
| Bernie
First things first-- You firstly need to see what has happened--so off with the head and go from there. There's obviously an issue there somewhere but could be anything, getting the head off and checking is the only way to track it down You can check the head/block with a straightedge and feeler gauges--very unusual for the block to need facing off --unless it's been damaged Even the cheapest nasty gaskets you can buy should last longer than that- Do the studs have plenty of thread ---are you retensioning the head after it's initial heatcycle Will be interested to see some pics when you get him off- Don't worry about being .040" over that's nothing to worry about. willy Payen gaskets are fine but always start them up without coolant first and get them nice and toasty to cook the sealant Then do a normal retension and add the coolant ----this method is advised on the gasket packaging sometimes depending where they come from |
| William Revit |
| I had my 2" mains 1098 bored to take Hillman Imp pistons which is a 0.134" over bore, 3 offset 0.025" and 1 offset 0.015" as per Vizard, and no head gasket issues, big bore gasket and 12G940 head but don't know if that really makes a difference. Smoothest A engine I've driven probably down to the lighter Imp pistons but rods, crank, and flywheel were also lightened. |
| David Billington |
| Thanks for that, Willy. Yes, I retention the head (cold) after first heat cycle. I’ll be taking the head off today and I’ll take some pictures. And I’ll check for trueness of head and block. I think I might try Minispares for a head gasket. Bernie. |
| b higginson |
| Head off. Blown Between 3&4 Checked head and block with straightedge and feelers and the only measurement I could get was 0.003 inch Between 2&3 on the block. All other measurements were Zero. So still can't figure out why it blew. The engine was not overheating. Managed to dislodge a couple of cam followers when removing the pushrods, so tappet chest off,good job it wasn't a 1275. Bernie. 
 |
| b higginson |
| Hi Bernie It might be an optical illusion but is the wall thickness between 3 and 4 narrower than between 2 and 3? What should this wall thickness be, anybody know? Looks like gasket is very close to the edge. But it’s hard to tell from the photo. Les |
| Les Robinson |
| Are you overtightening the head studs Bernie?
<<because over-torquing will almost certainly distort the gasket to the point where failure is likely to occur. The most likely areas are the fire-rings that seal the head face (chambers) to block face (bores) off. Particularly between the bores where the steel fillet inserts are in non-copper/composite gaskets, and where modified heads have been a little over-zealously ‘relieved’ around the gasket fire-ring line. Especially between the centre two exhaust valves.>> https://calverst.com/technical-info/torque-down-and-head-gasket-problems/ Over torquing the head studs crushes the fire rings to the point that the pressure is then spread over the entire head surface instead if being concentrated on the fire rings. This then reduces the pressure ( measured as per unit area) and the gasket is then likely to fail as the fire rings are no longer sufficiently clamped between head and block. |
| GuyW |
| The reference to “Especially between the centre two exhaust valves” is more applicable to 1275 blocks/heads. The small bore engines have a lot of meat there. Bernie, although the 1275 doesn’t have tappet covers, you can’t dislodge the cam followers as you can with the small bore engines. |
| Dave O'Neill 2 |
| Bernie
Just looking at it--it appears that the headgasket or head isn't locating on the studs properly and in this pic the fire ring on No4 has been hanging into the chamber---maybe last time the gasket was in a different position and it was hanging into No1 or 2 if it's a floaty fit- Just try sitting the gasket on the studs and check if it's held in place ,or has any movement backwards and forwards--By rights it should be held firmly in place by the studs-----check the head for this as well Also ,seperately, because you've had this issue previosly, maybe the head has been machined incorrectly. If the machine shop has their grinder set up wrong the head 'can' be machined with a trough through the middle. Measuring with a straight edge along the head won't pick this up but if you set your straight edge across the end part of the head beyond the combustion chamber and check the surface across the end there for trueness then that will check for that. Hmm--wrong gasket-?--just relooking at your pics, the sealing surface of your gasket between the bores 1-2 and I'd guess 3-4 if it were with us look wider than the matching part on the cylinder head--If the fire ring of the gasket is hanging in the chamber at all it'll burn up Did you have the correct gasket--was it a small bore on a medium bore block(yours) There are three std sizes your's being --Maybe you'd be best looking for a bigger bore gasket--doesn't really matter if the gasket bore is too big but it certainly won't last if it's too small Do you know the part number of this gasket shown in your pic--? |
| William Revit |
| James Paul, Maybe this comment from Vizard page 332 might explain your machining companies reticence about boring more than 0.020", see image, but also show they lacked knowledge of the engine series. 
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| David Billington |
| Thanks everyone for your comments.
Willy. I measured across the head between each of the chambers. I can see what you mean about the marks on the head looking like the fire ring on 4 is intruding into the chamber and when the new gasket arrives I'll do the checks you mentioned. I think the part number in the Moss catalogue for the old gasket is MST207 listed as a competition item made from copper and asbestos. The one I've ordered from Minispares is "What all the racers are using" and is a multi layer type. The head has had no work other than a skim by my local engine machine shop, which is a well respected company and have an A series "Guru" on the staff. Guy. That link is very interesting, particularly about overtightening. David B. That extract from Vizard is interesting. My engine is from March '65, or at least the car is, so I guess the engine could be earlier. Les. If there is a difference, that's how it came out of the factory as no work has ever been done on the chambers and the car had only done 7000 miles when I got it, so it was unmolested. |
| b higginson |
| The gasket in your pic isn't a copper/asbestos, it's a black composite--but that doesn't matter now A MLS gasket is definitely best choice as they don't have a firing ring as such---is it a Cometic brand---there is a little issue with some of those but we'll run that by you when you get your gasket----don't forget to get back to us when it arrives willy |
| William Revit |
| Now, that's interesting. I'm all agog now... Prop was a fan of Cometic as I recall, and he had plenty of practice:) |
| Greybeard |
| Willy. The old gasket is a copper/asbestos one, that is the other side view in the pic. The side you can’t see is copper. The new gasket from Minispares is by Victor Reinz . Bernie. |
| b higginson |
| Bernie, I think that Calvert's comments about overtightening refer only to gaskets like the Payen one, with fire rings. I think that logically, I cannot see that it would apply to the multi layer Cometic sort. |
| GuyW |
| True Guy- tweek them down hard- Bernie-yep thanks but it still looks like it's been a small bore gasket on a medium bore block, I'll look the Victor Reinz gasket up, we don't get them here Grey-Most of Prop's issue was that his head had been bored out for larger studs and it wriggled around everywhere but there is/was an issue with the MLS gasket as well, which we'll also double check when Bernie gets his new one willy |
| William Revit |
| New gasket arrived. Not what I expected.
I called Minispares and the guy said that there is no sealer on it, normal torque setting and as there appears to be no difference in texture either side, ( he thinks) to fit it with maker's name uppermost. It just looks like a normal gasket, although there does appear to be a very thin layer of metal between the top and bottom layers when looking at the edge. I am now paranoid about what Willy said about the fire ring intruding into the cylinder. If I run my finger round the top of the cylinder on 4, I can feel the fire ring is not intruding but is flush with the edge. Same on 2. It's as if the whole gasket should be very slightly more forward than it is. The studs do hold it firm though so it can't move. So, I've fitted it, torqued it to 42ftlb and am waiting for tappet chest gaskets before I fire it up. Bernie. 
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| b higginson |
| Shouldn't uprated studs (which you say you have in 1st post) have nuts torqued to 50ftlbs? |
| Bill Bretherton |
| That gasket does appear to be narrower between 1-2 and 3-4 so should be better than the last one you showed Shame it's not an MLS gasket but, if they've had success with them it's worth a go When you say you ran your finger around the edge on no4 and it was flush, was that on the block or the cylinder head chamber willy |
| William Revit |
| Hi Willy. The fire rings are well described. They're the only type I've ever used. If the Cometic gaskets don't have fire rings(or similar), what's used instead round the bores/combustion chambers? Just interested. I know they're supposed to be very good, and a tad expensive. |
| anamnesis |
| Willy. It was around the block.I can't upload a pic because apparently the file is too large. |
| b higginson |
| Bernie, so you have Paint as a program on your computer? You can open the image in that, then resize it to make the file size smaller? |
| Jeremy MkIII |
| Stuff on MLS gaskets.
“In a lot of cases, the minimum gasket bore size is dictated by the combustion chamber configuration, as opposed to the cylinder bore size,” — Jeff Evers, Cometic Gaskets" "Depending on the type of gasket you are using, you might have a large off-the-shelf selection of available gasket bore sizes, or you might have to make do. Then, there is always the option of having Cometic make you a custom gasket, if your desired configuration doesn’t exist already." https://www.enginelabs.com/engine-tech/engine/hanging-out-discussing-head-gasket-bore-sizing-with-cometic-gasket/ ------- And I found the answer I was looking for anout fire rings in composites vs MLS. "These design and construction elements are examples of why MLS is quickly being preferred over composite gaskets, which start out as a basic metal core with a pliable material such as asbestos applied to both sides. Asbestos was soon rejected in favor of less hazardous composites but the design tactics were the same: use a material that easily conforms to the imperfections of the block and cylinder heads surfaces. A flange or “fire ring” is then installed around the bore opening to retain cylinder pressure. Other types of sealant may then be applied around fluid openings, but the fire ring is still basically a separate element that has to be fixed in position on the gasket. In contrast, each layer of a MLS gasket is a single unit with the embossments acting together to perform the same function as the fire ring when the gasket is compressed." https://www.jepistons.com/je-auto-blog/seal-of-approval-the-science-behind-jes-pro-seal-mls-gaskets/ 
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| anamnesis |
| An-yep. the fire ring on an mls gasket is simply pressed into the steel sheet like a groove around the bore
I would have liked to run Bernie through the process of checking the gasket against the block(which he's done and sounds ok) and against the combustion chamber shape, but a bit late now, it's done and dusted. Having used a fair few Cometic mls gaskets ,they are 'adjustable' if they hang in the chamber a bit in a spot or two----Having the firing ring pressed into them makes it possible to trim the edges a bit for a good fit Hopefully Bernie's gasket fitted up to the head ok, it certainly looked more suitable than the earlier one. Bernie , do you have a part No for that gasket--just out of interest Thanks willy |
| William Revit |
| As far as I know the filler in the copper/steel sandwich gasket hasnt been asbestos for the last 40 years, and certainly on those which I have verified as not asbestos the reliability of the gasket depends heavily on the quality of the asbestos substitute. If that succumbs to heat and collapses the gasket is a goner.
About 20-25 years back we found that was an issue with MGB gaskets, had a number with fails between cylinders. Examined the filler layer and it was basically the pinkish material that SU carb gaskets are made from, and between the cylinders which hadn't failed completely the filler material was scorched and crumbling. Not only that, but some clearly had been double dipped with minor gaskets punched out of them. Fortunately for us someone else had supplied and/or fitted the errant gaskets. |
| Paul Walbran |
| I did a run of about 20 miles yesterday after a re-torque to 48lbft,(uprated studs) and all seemed OK, but the last one lasted about 6000 miles so we'll see. Willy, the part number for the gasket is GUG702506VR but I suspect that is a Minispares number and may not relate to any other supplier. Bernie. |
| b higginson |
| Found him Bernie Looks like it's good for your engine--German gasket and multi fit for all the small bore engines I was just curious as I got caught once with a genuine 850 gasket and it was too small in the bore for an 1100- both what we call small bore engines Looks like they're only doing the two though, small bore and large(1275)bore so most likely have increased the size of the small bore gasket to cover everything up to 1100--should be good to go. willy |
| William Revit |
| Bernie
Following this thread with interest as small bore too (my engine; others might say I am a much larger bore!) Thanks for the info the gasket Minispares sell: http://www.minispares.com/product/Classic/Engine/Cylinder_heads/Gaskets/GUG702506VR.aspx?100401&ReturnUrl=/search/classic/GUG702506VR.aspxBack%20to%20search Do you have a standard heater matrix plumbed in and using the standard route, and if not how did you plumb from the heater take off or using a blanking plate? I know you said you weren’t overheating but guess worth asking about the heater in relation to total volume water in your system plus possible scope for hot spots potentially exacerbated depending on how a heater delete is done (if it is). Also if you have a heater is it normally turned on, i.e, water circulating. Cheers Mike |
| M Wood |
| Mike
I have a rather convoluted heater valve usually found on FX taxis,from eBay. It allows me to control heat inside the car via an extra cable, while still maintaining coolant flow in the head.It works well. I'm sure it had nothing to do with the recent HG failure because I'd had a couple before I installed it. In the picture you can just see part of it, the brass bit, and I have since replaced the tap with an elbow for a Mini from Minispares. Sorry about the orientation of the picture, I don't know why it loaded that way. Bernie. 
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| b higginson |
| Bernie Glad to hear you still have the heater plumbed in and water circulating.. Good luck with the new head gasket. Cheers Mike |
| M Wood |
| I had the same problem as mentioned by Les Rose. The problem was shoddy machine work in the previous rebuild. Properly surfacing the block fixed this. I had installed 5 head gaskets after the previous rebuild, Payen and others only to suffer low compression and blowing out between cylinders 2 and 3. Good machining in the latest rebuild lead to and amazing running condition with no leaks at the head gasket. |
| Glenn Mallory |
| I had a constant running problem on removing the head I found that the gasket had blown between 2 & 3.
The gasket was Payen AF470. On checking witha local garage that does a lot of rally and race cars and has a dyno. The owner said that the AF470 were a problem. MED and Swiftune return their stock, The replacement is a composite gasket BK450.I'm in the process of refitting as I have changed the camshaft so I'v not run the engine yet. Minispares do a green gasket which is plastic that they use on their race engines and MED use BK450 on their race engines. |
| Peter King |
This thread was discussed between 08/10/2023 and 23/10/2023
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