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MG TD TF 1500 Oversize pistons or a sleeve? BBS discussion at MG-Cars.info
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MG TD TF 1500 - Oversize pistons or a sleeve?
| Just had the spare block back from Redi Strip and it looks really clean. The bore is on the edge though. Assuming no ovality in the bore, #3 is the largest @ 2.737" and #4 is 12 thou smaller (2.725"). Standard 1250 bore is 2.618" These measurement were taken with my digital vernier and will need to be confirmed with a micrometer at a variety of points in each bore before I make a move. Not much info in the archive. So the options are:
Find inexpensive NOS .120" or .125" over pistons and rings. Next to impossible. And on the very edge of desirable. OR Order these at about AU $2,000 for a set. Sleeve to accommodate .060" over pistons. Pistons and rings quite inexpensive (AU $310) and available. Sleeving all up less than AU $500. Unless someone is looking to get rid of .100" and .120" over and is happy to part with them cheap because of the risk involved with these bores, then option 2 seems the only way forward. Be great to get opinions from those who've gone down the 100/125 over route though? I'd like to find a balance between cost, risk, reliability and performance. Cheers Peter TD 5801 |
| P Hehir |
| Best get it measured up by someone I feel Peter i can't see how there would be .012" diff between two cylinders Can you measure the skirt of the 4 pistons, down the bottom at rightangles to the pin and we'll get more of an idea as to what you've got going there |
| William Revit |
| You really need to have the bore measured with a dial cylinder bore gauge, to exactly indicate the wear all around the top half of the bore, where most of the wear takes place. And have the bore measured in both dimensions, for ovality. I also suspect it very unlikely that there is .012" difference in bores.
If you decide/need to sleeve it, I would have it sleeved back to STD. That both provides the most ridgity for the block, but also allows most future re-boring. Perhaps you already have +.060" pistons in hand. Tom Lange MGT Repair |
| t lange |
| Sage advice. I could only measure the top 15 mm of the pots and had intended to have an accurate measurement done before making a decision. Surprisingly there was no sign of a lip at the top of any of the cylinders and the bores looked and felt fine, but this is no test, just an observation. I don't think I could bear sleeving it back to standard. I hope for another 20 years of spirited driving. Then the block will be someone else's problem. I still enjoy driving like a twenty year old so every bit of extra capacity helps. If the cam with the roller lifters in the engine in the car does what it's supposed to do, then I won't need it for a few years yet. I'm having the bore and the wall thickness measured accurately on Wednesday and logic dictates I'll almost certainly go with the resleeving and + .060" pistons. Unless the bores with a very light hone and the wall thickness checks out OK; AND someone wants to donate a schmick set of 0.120"/0.125" over pistons :-). Some XPAG's have been successfully taken out that far ... Cheers
Peter TD 5801 |
| P Hehir |
| Happy to swap a totally restored original MRN or FA ignition switch with a rechromed bezel, new lever, all NOS internals and an original unused Wilmot Breeden Union key, if anyone has a set of big pistons lying around. Cheers Peter TD 5801 |
| P Hehir |
| I wish the Aussie was in better nick as I've just seen on the FTFU site 100 and 125 over pistons are US $323/set! Cheers Peter TD 5801 |
| P Hehir |
| Peter
Have you had a chance to measure the pistons, i'm a bit interested to see what's happening there My suspicion is-- Because of the differences in bore size up the top and no wear ridge, either your measurements are up the creek a bit, we may possinly have experienced that earlier on, or probably what has happened is that the bores had a ridge previously and have been cleaned up with a ridge remover creating the discrepancy in the sizes up where you are measuring What size are those pistons--on the skirt--? willy |
| William Revit |
| Peter. Try Grahame Burling 38 Adams Street, Frenchs Forest , mob. 0412228235 who may be able to help you as he can supply made to order or hard to get pistons and piston rings - worth a try. John |
| J Walton |
| I can't answer that Willy. The pistons that I have were standard from the 4/44 and I'll be selling them along with a set of standard new big end bearings. The bare XPAW block has been sold. I'm using the conrods and the crank, which has been checked professionally. The mains are standard and the big end journals needed to be taken to 0.010". The XPAG block was nude and unused since the 60's so I've had to chase the components that I couldn't use from the 4/44. The XPAG bores are definitely way oversize. These are the VERY rough digital vernier measurements, as we all agree this isn't the tool for the job. I've just checked each bore again three times N/S and E/W at the top of the cylinders and the results were reasonably consistent suggesting some variation between cylinders and are as follows;
#1 2.733"/2.737" #2 2.732"/2.731" #3 2.737"/2.737" #4 2.734"/2.732" The biggest dimension is 2.737" which is 0.119" oversize. I have no idea yet of the bore size in the gudgeon pin region where the skirt spends most of its time. I'll have the bores and walls measured accurately on Wednesday using the bore gauge and the wall thickness indicator and post the results. So I'm still unsure whether oversize pistons or a sleeve is the way to go, as both approaches appear to present issues. Ideally if I have the wall thickness after a hone, (apparently there was some variation in castings), then my preference would be to go out to 0.125", simply to regain the zip lost by fitting the 4.3. I'm encouraged by the fact that FTFU sells pistons at this size. So this has to be possible. Whether it is desirable of course is a whole other matter, hence the original question. I'll give him a call John. Cheers Peter TD 5801 |
| P Hehir |
| John, Grahame has retired but will call a couple of people on my behalf who might be able to assist me. The feedback I have is to stay away from used pistons. This sounds like good advice. Yes? Cheers Peter TD 5801 |
| P Hehir |
| The answer to my query comes from the block itself. An engine rebuilder using a dial gauge has measured the wall thickness at all 16 water jacket holes surrounding the cylinders and the results indicate that the only way forward is to re-sleeve; even though 15 of the 16 measurements fell between 0.160" and 0.200", more than adequate for + 125" pistons. But #3 only showed 0.070" on the front jacket/left hand wall. So I'm taking his advice and going with a new set of + 0.060" pistons and having the block re-sleeved. Cheers
Peter TD 5801 |
| P Hehir |
| Who with Peter. John |
| J Walton |
| Peter why are you not leaving the engine bores at std with the new sleeves? That way you have more meat in the cylinders to work with later if needed. |
| W A Chasser |
| John, the assembler is up the mid north coast and does a lot of engine work for central, rural and northern NSW square rigger owners owners. He has a terrific rep for working on XPAG's. You know who used the dial gauge. Things were looking good until we hit #3. :-(
Bill as I have to sleeve, it just makes way more sense to me to go to 0.060" over, simply for a bigger capacity and a little better acceleration, as I'm running the 4.3 rear. I may not still be driving in twenty years time, though I certainly hope to be, so further rebores are not a concern. This backup engine and gearbox is going to be on standby if I do have issues with the roller cam setup in the car now. I wont know that until I'm able to complete the few remaining items prior to starting up the engine, so it would be great to be able to just change the lot over if it all goes pear shaped. So 0.060" over it shall be. When I finally do part company with the car it will come with two complete engine/transmissions and sets of ancillary equipment. I have been collecting components for years. I'm not able to drive with the meds I'm on now, the car is 5 miles away, and Covid and the surgery has slowed things somewhat. This rebuild is happening largely over the phone and on the net with me gathering all of the required parts so as not to delay the builder when I'm ready to give him the word. Cheers Peter TD 5801 |
| P Hehir |
| Four new 0.060" over pistons from Auto Surplus are on their way. Includes rings, gudgeon and wrist pins as well as a set of King big end bearings @ + 10 thou. AU $376.20 plus $20 shipping from Bendigo for the lot. Best deal that I could find anywhere. The bottom end components are now sorted. Cheers Peter TD 5801 |
| P Hehir |
| The bolts holding the gudgeon pins need to be replaced. The original types require a special tool and the torque is critical. While you can fabricate a tool by grinding and turning a spare socket, even then torquing them is touchy. I would strongly suggest you get a new set from Tom. His have a hex socket and this makes torquing them a breeze. Jim B. |
| JA Benjamin |
| Just saw this. Thanks Jim. I'm definitely using the ones with a hex socket. The problem before I weigh and balance each of the conrods (I have a large old set of scales that weigh to 1/10 of a gram,) is finding a Whitworth socket to sacrifice. I don't want to ruin one of a set of 10 new Whitworth sockets just for this one operation. And I take your point about torquing. The little end bolts didn't come with the new piston and ring set even though I did ask if they were included. Cheers Peter TD 5801 |
| P Hehir |
| Well the little end bolts that I just removed from the 4/44 standard pistons WEREN'T Whitworth heads! So much for all of the bolts in the engine being Whitworth with metric threads. We used a 13 mm open ended spanner without any drama, which was a nice tight fit on all of the the bolt heads. The 1/4" Whitworth was a sloppy fit. Good thing I didn't ruin a Whitworth socket! The con rods and caps were marked 1, 2, 3, and 4 and three of the pistons marked (C433) and rods (Mowog 24005 BH Star 1), were obviously original, the #3 - (Mowog 24005 Star 71) (No BH letters) - was a ring-in. It also had an unmarked piston. I'll check these numbers out.
Now to do some weighing of the rods. Overall weight first, just because I'm curious, then I'll do the little end/big end using the purpose made test stand and finally balance each of them so that they match the lightest of the four. I'll hold off until I have the little end bolts. Some useful 'how to's' on You Tube. The idea is to have the assembler spend the least amount of his time and my money working on the installation of the crank, cam, followers, bearings, timing gear, main and big end bearings, pistons, rings, pressure plate, crank pulley & shim, dog and the final balance. Cheers Peter TD 5801 |
| P Hehir |
| Peter If you're going to get into balancing these rods your self you need to have a good weighing up session first and determine which end of each rod needs attention, don't get caught out by matching the little ends first, The little ends have little effect on the weight of the bigends but depending on how much you have to remove from the caps on the bigends then this will alter the little end weight- So bigends first then little ends Any pics of your weighing setup------- |
| William Revit |
| Peter
If you're going to get into balancing these rods yourself you need to have a good weighing up session first and determine which end of each rod needs attention, don't get caught out by matching the little ends first, The little ends have little effect on the weight of the bigends but depending on how much you have to remove from the caps on the bigends then this will alter the little end weight- So bigends first then little ends Any pics of your weighing setup------- and the package from victoria, i'd be leaving that untouched for a day or two with what's going on there |
| William Revit |
| That's tricky, i wonder how i did that |
| William Revit |
| Thanks Willy. Double the value I guess. :-) The package came from Bendigo, which is well away from the hot zones, so I'm hoping all is good. I could mess about making one from ply and some brackets. There's a nice DIY one on You Tube, but making it seems an unnecessary deviation. I'll use my heavy scales and the borrowed genuine rod attachment from a mechanic mate. Big end first it shall be. The different rod may well be a different weight. I'm hoping the other three will be really close. Doesn't matter though as I have a good linisher and I'll proceed with caution. I'll also review the four or 5 posts on You Tube and go with whatever suggestions make the most sense. I'll take some pics as I go and write a piece for the mag. Just on the subject of bores I met an owner today who's rebuilding a TF engine, whose bores are 0.160" over, which seems outrageous! I have no idea where the pistons came from but the cylinder walls were paper thin. Needless to say this is why he's changing the block. Cheers
Peter TD 5801 |
| P Hehir |
| The boss has an unused set of digital kitchen scales. I'm in trouble if I damage them as they have a glass top and are about the size of a paperback novel. They'll weigh from 5 kg down to 1 gram. I kept her calm by using a clear plastic takeaway food container lid so I could read the scale and zeroed using the TARE function. These show all four con rods within 2 grams of each other. I'll remove the old big end shells and weigh them again. Obviously 1/10 of a gram is ten times better than one gram when balancing. What tolerance do/did/should XPAG engine builders work to does anyone know? (For those unused to the metric system there are 28 grams to the ounce.) I have another set of heavy large old school balance beam mechanical scales accurate to 1/10th of a gram and I'll probably end up using them, but is this overkill? I'd like to hear opinions from professionals or serious amateur engine builders. Plenty of conflicting advice on You Tube. Cheers
Peter TD 5801 |
| P Hehir |
| Advice offline says within 0.1 gram if you're going racing, 0.5 gram seems common and 'within a gram and you should be right buddy' was the biggest margin. Obviously less is more. Odd advice on where best to remove metal; either the side of the wrist pin housing NOT the bottom cap or the reverse depending on who you talk to. Even some who say balance the little end first. But I'll follow Willy's advice on the order.
I'll try for the same weight - within 1/10th gram, weigh the big end and correct there first and then do the little end. AND I'll leave the bottom cap alone, removing the minimal amount of material from the wrist pin housing. Unless someone has a serious reason for not doing so? Once I've removed the bearing shells, given the conrods a good clean, weighed and fitted the new wrist pins, I'll get underway. Cheers Peter TD 5801 |
| P Hehir |
| Peter
If you have a set of rods within 2 grams dif. that's a pretty good set of rods to start with---You could just run them as is- A 5c piece is 3 grams -A4 sheet of paper is 5 For a std roadgoing T type you're well inside already, most are 10/15 grams out, or more If you're going to balance them the target to aim for is within .5 of a gram on either end and .5grm total weight for a performance balance job Going for .1 of a gram is full on big rev racer stuff You'll find plenty of places to remove some metal up the sides of the bigends near the joint with the cap, there's usually a few bits and pieces poking out that can be buzzed back a bit there On the little end you can just do a little 45 deg.chamfer job around the top edges, it doesn't take much to make a difference willy |
| William Revit |
| Thanks Willy. Your advice is always appreciated. I'm sure others as well learn considerably from your posts. Again many thanks. Cheers Peter TD 5801 |
| P Hehir |
| Peter
Just to explain my reasoning for doing the bigends first If you're taking metal from along the sides of the bigends, then it's probably not so critical which end you start, more of a habit thing really The reason for starting at the bigends on some rods is that some rods actually have a pad on the bigend cap specifically for balancing, Later square-cut MGB rods are built like this so bigends first for them as the pad is well out past the centreline of the journal and removing metal there has the cantilever effect of adding a little weight to the pin end, not much but enough to put it out if you've done the pin end first. not really an issue with a T type as there is no pad and metal would be removed from the sides of the bigends All a bit of a balancing act really----------lol willy |
| William Revit |
| Pete Hehir,
One thing you want to watch out for when installing sleeves, is the parallelism of the sleeves. In my shed, I have spare block, sleeved out to 1460, So I had it checked for geometrical authenticity with the intention of rebuilding to to modern specs. I wasn't surprised to learn the only two of the cylinders, were perfectly parallel; the others at some cockeyed angles! I have never liked cutting into the water jackets. Once the material of the bores is removed, the block looses some of its structural integrity; and because most sleeves are very thin, I don;t see how they can return the block to its original strength. It the case I have quoted above, in my case, the block ended up with 3 sets of bores, all going in a different direction! I have no idea what effect that would have on a rebuilt engine - maybe none, but I can't help but think, that having all 4 bores identically parallel, is not the ultimate solution. Gord Clark Rockburn, Qué. |
| Gord Clark |
| Thanks Gord. Sleeving a block is one thing I'll leave to the professionals. The guy who's doing mine has done scores of XPAG blocks so I believe I'm in good hands. Once he's got it in his machine shop he'll no doubt make me aware of any issues. Thanks for the post. Cheers Peter TD 5801 |
| P Hehir |
| Nearly there now. I've had the rear main bottom cap machined in concert with the rear upper and lower white metal bearing shells in order to help minimise rear oil seal leaks. The final hurdle is a suitable cam. I'd love to be able to locate an original TC early TD cam in good condition, complete with a timing card, as these had a wilder profile than later TD, TF and 4/44 cams. I have a 5/45 and two re-profiled cams in good nick, but of unknown parameters. It'll cost me $100 just to get a timing card for each of them! I have a lead on a re-profiled cam, again of unknown detail that I've agreed to purchase. I also have the option of a purpose ground Aussie billet cam for about $700 AU, an off the shelf item new for $450 +, both of which are at the top end of my budget. Somewhere in all of this I'll end up with a cam that works with the bigger exhaust, machined head, carbies, TF valves and springs, bores and pistons, in my balanced and carefully built back up early TD engine. The journey continues. It seems the original early TD vertical oil pump can and filter is just not available. Can someone, somewhere prove me wrong? Cheers
Peter TD 5801 |
| P Hehir |
This thread was discussed between 11/07/2020 and 27/07/2020
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