Forum for discussion of MG and MGB motorsports, historic and current (SCCA, NASA, VARA, etc) car preparation, engine, bodywork, suspension, drivetrain modification.
My car was running real good with the turbo on my 79' 1500 midget, but then I blew the Payen head gasket. The head was rebuilt and decks of the block and head were good. Is there a better head gasket than Payen for my 1500?
Mark, I know of none but the deck of the block and the face of the head have to be as smooth as a mirrie in order to get a black, Payen gasket to work. Basil PS - got home a little while ago and It's too late to call. I sent you an email - let's talk Friday (I'm sleeping in so not too early) Basil
You may check with Cometic, I'm not sure if they make one for the 1500 or not, but these head gasket are what we used to seal up 15 to 1 A series race engines, their website is www.cometic.com . The head gasket arrangement on the 1500 is unique it has recessed area in the block deck for extra fire ring material in the gasket to aid in seal, if you start decking a 1500 block, then this is compromised, the recessed area are now more shallow and the gasket will not seal properly, with the 1500 race engines we had to deck block until the recessed areas in the block were gone, use a short compression hieght piston and then the 1300 head gasket. I have no idea if you decked the block on your 1500, but thought this was worth mentioning.
FWIW, I checked Cometic's site they show a 1500cc (look under Triumph) copper .043" head gasket, the one I use on the 1275 is the MLS design which is a three piece all metal unit, we had really good results with the MLS unit on the 1275s and the 948s. You can custom order a head gasket from them, and even vary the thickness on the MLS head gaskets it may be worth asking them about, the biggest issue here is how the recessed area in the block is handled.
Here's a photo of the area that blew. No decking done to the surfaces.
Thanks for the info!
I have never seen the inside of the block of my 1500, i.e. never had the head off. Looking at the picture provided, am I correct in seeing these two bores siamesed together with no deck sealing area between them? Is this what is being referred to above as "the recessed area?" How would you ever seal these two cylinders from each other? Are there metal O-rings in the head gasket to seal these two cylinders? Sorry if this is a sophomoric question, but a 1500 rebuild is in my future and I am trying to learn what I can prior to. Additionally, are the stock 1500 pistons dished, as in Mark's picture, or are these specifically for his turbo?
The Cometic head gasket is 5X the cost as one from say Moss. For those with more experience, is 5X the price worth in quality and longevity, etc, for a slightly hotter than stock rebuild?
What does performing this "milling of the block" do to piston, rod, and crank selection, i.e. are there shorter deck or dished pistons being produced, or shorter rods, or a destroked crank, to compensate for the loss of the block height to keep compression ratios down, or are any of these necessary? Off hand I'd assume someone makes a piston with the correct deck height to compensate for the loss of the block surface?
Well looking at the picture Mark has shown us of his block deck, it appears very little material has been removed, this was a lower compression engine to begin with, around 8.0 to 1, which should handle about 8-10 pounds of boost. As for pistons available in different compression heights for a 1500, there are not any of the shelf offerings, other than some have use TR6 piston in 1500 blocks (which have a much lesser compression height, and reqire alot of block decking) , but any piston can be custom made in any compression height with almost any piston top you can imagine, for a cost. Bottom line if you start making any considerable cuts to a 1500 block deck, then you will compromise the recessed areas around the cylinder bores that the 1500 head gasket uses for seal, at that point you must deck the recessed areas completley out of the block and use 1300 head gasket, which means you need a custom piston . Using the TR6 piston is a tricky deal, Rick Cline of Triumph racing fame came up with the recipe to use the TR6 piston in the 1500, the deal is they are like .250" shorter in compression height, and you can get close to the freeze plugs at the rear for the block when you deck the block enough to use them.
Hello Mark:
My name is Ivan Sotomayor, I live in San Juan, PR. I am the owner of a 1500cc 1978 Mg Midget. I made it turbo almost a year ago. I beleive i have blown my head gasket as well. I found you thru http://www.mgexperience.net/phorum/read.php?41,1374117. I have replace three blown gaskets PAYEN since I made it turbo. I was wondering what you did to solve this issue? I am running my car with 15psi boost and I upgraded the compression to 9.1. I also made it Fuel Injection and I am using a Microtech computer. I upgrade the camshaft to a race one sold by British Northwest parts. I bore my cilinders to .20 and I am using flat top AE Pistons. Have you had any trouble with your piston rings?
Did you tried the Cometic Gasket?
I hope you could help me because i am getting pretty frustrated.
Sincerely,
Ivan
Buenos tardes, Ivan, and welcome to the Forum. I'm sure you'll find friendly and helpful advice here on the Forum, and might I suggest that you start a new thread on this topic? I think you'll find better response than renewing this older thread.
You'll find that Hap and many others will be tremendously helpful to you. I'm less familiar with the 1500 engine than I am with others, but I'm sure you'll find new friends and new information here.
Cheers and welcome,
Dick
Thanks a lot Hap for your quick response. Yes, i installed ARP bolts to the head! However I didnt know about the 5 ft lbs torque! Great Tip! I will give a try to the copper gasket provided by Cometic before reducing the block since that would considerably increase my compression since I replaced my pistons to flat top plus bored to .20 over factory. But if i decide to reduce my block top, besides using the 1300 gasket, do I have to replace pistons and rods? What about engine temperature?
I have noticed that I always had blowby on my engine even before the turbo induction. But it got agravated after the induction. There is oil spiting out of the oil stick. Serious white smoke is coming out of the valve cover thru the catch can breather. Could it be the piston rings? or is the same story with the gasket? How can I make a crank case breather for blow by? Is theres ANY way to totally eliminate the blowby to my crank?
I know too many questions! But I would appreciate what you can answer.
As soon as I get home today I will post pictures of my Feroz!!!
Should you have time check out on my Facebook profile link below some pictures. The second link is a video of me testing my car and you can even see a light smoke coming out of the valve cover. on the third link is me trying my Feroz in the Dyno an you can see there is no smoke that time coming out of the catch can. The time between the 3rd video and the second video is only days.
https://www.facebook.com/media/set/?set=a.326370655234.339262.898535234&type=3
https://www.facebook.com/video/video.php?v=385988325234
https://www.facebook.com/video/video.php?v=348552670234
The flat top pistons in a 1500 are the 9.0 to 1 pistons, and then add 15 psi of boost to that, in my opinion, that's too much compression ratio for that amount of boost. Not that people don't get away with it, they do, but always at a cost, high boost in a forced induction engine is easy way to make power and you can get some unreal numbers, but the cost of that is engine reliabilty. There is guy I know, has a late model VW Beattle, he's got better cams, adjustable cam gears, probably a few other tricks I don't know of, he gets serious work done to the car at my buddy's import shop, he is running 14 psi, in the last year he had first get the head rebuilt, and now the entire bottom end, high boost comes at cost.
One thing I do need to add here, when working with a MG/Triumph 1500 or TR6 recessed block engine, if you deck the block, which should only be if you fail the straight edge test, then you can only deck the block very minimumally, say just a clean up of .010" or so, should you ever deck a Triumph reccessed block .020" or more, 1500 or TR6, you will compromise the head gasket seal, and from expereicne, let me tell you, this is not something you want to do. In theory the recessed blocks with the extra head gasket fire ring should have been improvment in head gasket seal, but it didn't work that way for these engines, almost everyone performance or race building of these engine goes back to non recessed block set up.
Hap:
Any suggestion on Forged Pistons for my car?
Have you used total seal rings?
Ivan
I love Total Seal and use them on all rebuilds, regardless of make.
I am curious. What would the static CR be for TR6 pistons and decking off the fire ring only? Would 15# boost be enough to make up for it or still far too low?
I don't have a dog in the fight, just curious and too lazy to look up the information and calc it myself. ;)
Sorry Mike got lost on your question about the 15# boost! Pls be more clear.
Hap, I removed my head and the gasket was not my problem for the serious blowby. I had too much compression coming out of my valve cover. Question? What is the perfect clearance for the pistons with the rings. If i bored my cilinders to .20 can I still use the cometic gasket that you suggest me last time?
Thanks
Ivan
TR6 piston requite alot to be taken off the block, even with a high boost forced induction engine. At near zero deck hieght on a race engine suing TR6 pistons, a Rick Cline formula, it was like .250" off the block, it's get dangerously close to freeze plugs on the back of the 1500 block, I done two race engine using this formual and the only reason to go this route is to save on piston cost, I think coming up with custom piston with a better compression hieght is a much better choice, more costly, but less lieky to be a issue with the block, I have a 1500 block in my shop right now, somebody goofed up by taking too much off it, they got into freeze plugs, it's now scrap metal.
Hopefully more clear:
I was just wondering...
1) What would the approximate static CR be for using the mentioned TR6 pistons in the 1500 block when you only mill the block down enough to remove the fire ring?
2) Would 15# boost be enough to compensate or is the resulting CR so rediculously low that it is a "non-starter" figuratively and literally?
Better? :)
I was just wondering...
1) What would the approximate static CR be for using the mentioned TR6 pistons in the 1500 block when you only mill the block down enough to remove the fire ring?
Michael, It would be too low, the recess is maybe .060" deep so it would still give you deck height of near .200", so it would have the compression ratio of hit and miss engine :D
2) Would 15# boost be enough to compensate or is the resulting CR so rediculously low that it is a "non-starter" figuratively and literally?
I went over this with a guy doing a turbo MGB one time, he was shooting for 10 psi of boost and wanted pistons with a CR of 7.0 to 1, I talked him into 8.0 to 1, I think then the deal would be, it would bo a total dog until the forced induction kicks in. You would have engine that felt like it had absolutely no power, then once the boost kick, it would take off like a rocketship, I think that would make for terrible street engine. Of course none of this would work for the 1500 with the TR6 pistons because it would be more like 5.0-6.0 to 1, or something crazy like that, it would be lucky to even run at low of CR.
Ok, also keep in mind you can cut the living crap out of the 1500 head, we would cut .100" off them to just get to 11.0 to 1 with a near zero deck height, and 1500 carb racers would cut alot more than that, I've never built a full prep high CR 1500 race engine, but it would be one helva slice off the head to get up there in SCCA high CR area, like Steve sargis runs in FP in the SCCA. Note, you can do anything more than say a servicable skim cut on 1500 block is the most you can do, if you say cut half the recession, say .030", the the head gasket will not seal, once you decide to starting doing considerable decking to a 1500 block, it get rid of all of the recession or nothing, but a skim cut.
Actually you don't see alot of love from the 1500 street crowd when it come to performance, no one in the US builds them with passion for the street like they do the 1275s, but with the right parts, it could be a for sure be a 1380cc killer, I've always wanted to build a serious street 1500 perforamcne motor, but those guys don't seem to go that route, but it will come over time, and I'm ready for them when they do. :)
Thanks! 6:1 is low allright!
And I see what you mean about the turbo kicking in... old-school Porche x10.
Thanks Hap:
BTW I am more than clear that I should lower the 15#psi boost for the next time, and I WILL!!!. Ok I included 2 pictures on this thread. Do you see too much clearance between the pistons and the cilinders? Remember my car was running super, after a few rocks, white smoke started flowing out of the valve cover.
Please look at the other pictures I included below for a total of 4 pictures. One of my pistons was giving me 60cr, and the other three gave me 145. Car was accelerating incredibly with those numbers, at low idle no feeling of damage was perceived it was smooth at idle speed (1000rpm). But white smoke kept coming out of the catch can and when I took the oil stick lots of oil coming out. Thus, lots of compresion expressed at the crank case as well. At first I thought I have blown the gasket, but gasket was perfect, no signs of jumping compression from one chamber to another. So, my theory before pulling the pistons down is that I have too much clearance in the pistons or since I used factory piston RINGS they are fatigated, thus compression is going down thru the clearance that I have.
Please what would you recommend me to do at this point. Besides avoiding the 15#psi. jajajja Please remember I am in Puerto Rico and we do not have too many experienced people with this type of engines. As a matter of fact, when I take my parts to the machine shop surprised faces I always get.
Kindly your thoughts, for a very frustrated "Fiebru"
I'll be the first one to say that I'm not familiar with the 1500 motor, but, dang, it sure looks like twenty over pistons and rings in sixty over bores... ::o
In pretty much all the engines I've ever worked on the piston-to-bore clearance was measured in thousandths of an inch, and it looks like you could measure these with a yardstick. Similarly, the rule of thumb for compression ring end gap is .003-.004 for every inch of bore, so I'd be looking for, maybe, .012-.015 end gap on the top ring and, unless my eyes deceive me, it sure looks like the end gap on the top ring is at least 3/8 of an inch.
Whassuppp?????? :S
Hap? Hap?
Dick
"it sure looks like twenty over pistons and rings in sixty over bores... eye popping smiley "
UMMMM>>>> More like +.160 or maybe +.260 About enough for the rings to jump out altogether.
In fact, pic #4 looks like some of the top ring in the LH cylinder has already traveled elsewhere.
I can't wait for Hap's comment!
FRM
Hap:
Another question? Are you supposed to have even more clearance when the piston goes down rather when hits the head? In another word is the cilinder wider in the top rather in the bottom? as we can see on picture #3?
Ivan-
I suggest you get some books and start reading, and some measuring instruments.
Cylinders are straight up and down, until they wear. Extreme wear would be .010" at the top of the ring travel, and maybe .006 at the bottom, with less wear in the middle of piston/ring travel area. The clearance at the top of the skirt just below the rings should be around .003; you cannot measure that with the pistons in place. Around the top of the piston, the clearance will be greater, maybe .020max all the way around, but nothing like what you have.
I don't know what is going on here, but it really does look like the pistons are simply far too small for the bores.
Stock 1147 bore = 2.728 +.020= 2.748
Stock 1296/1493 bore = 2.900 +.020= 2.920
Piston size at the top will be smaller, exact number depending on piston manufacturer, but about .020 less than bore size is typical A well used standard 1300 piston I have here measures 2.902 across the skirt and 2.873 across the top.
Crazy as it seems, it looks like you have 1147 +.020 pistons in a 1500 block!
FRM
Thanks, Yeap I will read. Last time i did trust a local mechanic that apparently either him or the machine shop didnt pay attention to this important detail. But after today I will have to study and learn how to do it myself. I do not want to get ripped off again.
Thanks again for your help.
Very confusing! The number 20139 on the pistons appears to be correct for 1500, though there are some bizarre parts listings to be found. Bad part is that that means the bores are really OS. You may have to sleeve it. $$$$!
FRM
Yeah, the piston to bore clearence does look huge, on a engine with this bore size it should maybe .0025" measuring the piston opposite the pin bore. I can't tell in that one picture if I'm looking at the top compession ring gap or not, could be a shadow or discoloration, but if that is the ring gap, not good, with this bore size, ring gap would be maybe .013"-.014" tops, without doing the math.
I always use this formula for ring gap
top comp ring: bore size x .0045"
2nd compression ring: bore size x .0035"
Oil control ring minimum of .015"
(note in some stock LBC pistons, they have three compression rings, use 2nd comp.ring formula for 3rd comp. ring.)
This is pretty common ring gap formula, it comes with most of all the high end rings, the ring gap can be slightly increased for a forced induction engine, but we're only talking a extra thousands or two.
Hap, Fletcher:
Thanks for the info!! I pulled out my pistons today, The pistons measures are 2.895 bottom and 2.918 at top without the rings. Pistons have very very small chip where the rings go. Rings were broken. However the sleeves are in perfect perfect condition. I am assuming that with those measures my bore would and should be 2.920. If the bore is 2.920 where can I purchase forged pistons with that exactly measure?, so I only have to give honey to make .003 clearance to the cilinder and plug and play. How about the JE Forged pistons that you reccommend me last time.
Gracias
Ivan
Ivan-
DO NOT ASSUME ANYTHING!
You MUST accurately measure the cylinders, at numerous locations, each cylinder, then decide what to do. Normally, you have the pistons in hand, then match the cylinder sizing to give the clearance the piston manufacturer calls for. Getting pistons matched to existing bore sizes would be very special order, and certainly makes little sense unless the bores are perfect and the size known known exactly, within tenths - .0001.
Would like to see pics of your dead pistons. The numbers you give are goofy - show us exactly where you measured.
FRM
I took the measures from the top exactly at the crown
and the bottom exactly 1/4" from bottom of piston
"Pistons have very very small chip where the rings go"
Pretty quaint description of pistons with half the ring lands missing!
Read everything above again. Read more books, think.
Basic piston measurement is just below the oil ring at 90 deg to the pin bore. That's the one you work from for clearance. Top of piston is usually smaller, by up to about .020.
Bottom of the skirt, again at 90 to pin is sometimes bigger, maybe by the clearance figure but no more. If bottom measurement is less than first measurement, then the skirt is collapsed. These are really collapsed, if you measured right!
FRM
Fletcher look closely to pic #3. Next to the Flash thats the chip I was refering to. (Not the rings) anyways the reason for me to be sahring info, pics etc is beacuse I am certainly not an expert on this field, nor a mechanic. Nor I have found and expert on this type of cars in the Island.
Although I am reading as you suggested me, my intention with this sharing is look for professionals and experience people who can help me to enjoy my car.
I will post my bore measures in the near future.
Thanks
Ivan, Pistons are conical in shape, if that the right term, meaning larger in diameter at the bottom of the skirt than compared to the top of the piston, bascily this is done because there will be more heat expansion at the top of the piston, where the heat is. Ok with that being said the industry standard of where to measure a piston for actual size is opposite of the pin bore center line, that is the location on the piston used to reference the piston to bore clearence. On your engine that would be, roughly 2.9ish bore, that would be say .002"-.003" piston to bore clearence.
