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MG Midget and Sprite Technical - the bad history of the 1500 crankshaft

i no ther is a bad history of the lower end of the 1500 engine . is ther any one that makes racing crank and rod sets for these engings . i am curently rebuilding my performance engine because it spun a rod bearing. . i do all my own work on the building part


any ideas

thanks

Michael Koegel

Texas


mck mike koegel

With enough money anything is possible. I think Carillo do 1500 rods.

Cambridge motorsport made EN40 cranks for the 1300 midget of their own design.

Or do you just mean bearing sets?

I expect Deb will be along shortly to tell you more and prices!


Daniel Thirteen-Twelve

For here in the states try acmespeedshop.com you can find there ontact info on there website, "Hap" would have a good idea of whats avialable fr the 1500

If you got a full grown money tree in your back yard try these guys I think all 4 make custom cranks out of EN40B material

http://paeco.com/
http://www.carrilloind.com/WhatsNew/tabid/55/Default.aspx
http://www.pauter.com/
http://www.morspeed.co.uk/ (make sure you click the red enter button to advance the pages

But As Danial makes Note...You best source is Deb Evans with pristist race engines, I dont know anyone that knows more about high performance triumph / midget 1500 engines then Deb... (pr.engines@tiscali.co.uk)

Prop

Michael

Your car looks very similar to mine...hope I don't suffer the same fate!

Nothing to add here, but I'm interested in whatever you may find out.

I'm planning to rebuild my engine next winter (going through the running gear, brakes,clutch hydraulics, etc. this winter).

Thanks for the post.
Dave


Dave Rhine

There is a lot of misconception about the 1500 motor fitted to the later Midgets. This is also further fueled by 'armchair experts' who pontificate on and on about something of which they know about the square root of F all (and who probably wouldn't know how to build a reliable motor anyway!).

In order to understand the limitations of this motor one (ideally) needs to know (at least some of) its development history.


The following is an excerpt taken from an article I wrote for the MGOC regarding the Midget 1500 engine:



In 1968 Triumph became part of BLMC who were intent on cost saving such that in 1970 a major revision was made to the engine with the release of the Spitfire MkIV. It is this revision that would become the Achilles Heel of the later engines. The change centred primarily around the crankshaft. In order to rationalise machining operations the journal diameters were increased to the same size as those on the 6-cylinder engine (as fitted to the Vitesse, GT6 and TR5/6). Journal diameters increased from 2.0005” - 2.0010” to 2.3115” - 2.2120” (main bearing journals) and from 1.625” - 1.6255” to 1.875” - 1.8755” (crankpin journals). In doing so this made the crankshaft heavier with larger diameter but narrower bearings. Thus the later 1296cc crankshafts have more bearing drag than the early ‘small bearing’ cranks and, with the increased weight, take more power to accelerate.

Unfortunately BLMC compounded this by downgrading the steel used for the crank from EN40B to the far inferior EN16U. Given that the engine is a 3-main bearing design, the use of a heavier crank in an inferior material means that crankshaft flex starts to become a problem, hence the late 1296cc and all 1493cc engines are referred to as ‘floppy crank motors’. At some stage in the design of the engine (from 1296cc engine number FH25001E and all 1493cc engines) the cylinder bores were also recessed which was said to improve the sealing of the cylinder head gasket (even though earlier units had not had a problem). This would limit the safe over boring of the engine to a mere 20thou and, in fact, can cause problems with detonation in tuned motors. If overboring greater than 20thou I deck the block flat and use the earlier 1296cc head gasket. Doing this will also mean that the pistons will need to be decked so as to give 20 – 25 thou clearance beneath the head gasket.

In 1972 the engine was again increased in size by stroking it to 87.5mm giving 1493cc. By this stage the engine really was at the limit of what could be done to it and the fact that it had a ‘floppy’ crank coupled with such a long stroke meant that failures would be commonplace unless certain aspects of the design are addressed. Fundamentally, for the reasons discussed earlier, crankshaft flex on the 1493cc motor is a major concern since it can rapidly lead to the oil overheating causing oil film breakdown with concomitant damage. Given that the motor is a 3-main bearing design, aside from the stroked crankshaft being poorly supported, it is the centre main bearing that feeds numbers 2 and 3 big ends. Any form of oil film breakdown will rapidly lead to wear of these bearings and, if not caught soon enough, a connecting rod (usually number 3) making a bid for freedom at high speed through the side of the crankcase. This is one of the reasons why the 1493cc unit cannot be revved like its smaller brethren.

However these failings can be addressed so as to produce a reliable unit with longevity between rebuilds. Primarily it is the oil system that should be sorted out, since this is at the heart of the problems. Fundamentally it is high oil temperature leading to oil film breakdown that kills Triumph 1500 engines. For this reason it is ESSENTIAL that an oil cooler be fitted; a 13 row by 235mm cooler is perfectly adequate (although for 'hard' use a 16 row is better). This is especially the case with the 1500 Midget, since it has the lowest overall Factory gearing of cars fitted with this power unit, as well as an engine bay that runs far hotter than (say) the equivalent Spitfire.

In terms of the oil being used you MUST use a good 20/50 (with ZDDP to prevent tappet wear) and change it yearly or every 6000 miles (whichever comes first), my personal choice is for Valvoline VR1 20/50 Racing. If the engine is in any state of tune (Stage one upwards) then use a 20/60 such as Penrite HPR 30.

Having sorted the oil and oil cooling, then modifications can be made to the oil system to increase its efficiency. Firstly it is essential to use the later type oil pump. This has an angled pick up that sits lower in the sump and better resists oil surge (if surge becomes a problem such as on Track Days then a single longitudinal baffle can be brazed into the sump, or better still a 'Windage Tray'). Additionally care should be taken to reduce the endfloat on the pump to the minimum quoted figures:

Inner Rotor endfloat – 0.0004”
Outer Rotor endfloat – 0.0004”
Rotor Lobe clearance – 0.010”
Outer Rotor-to-Body clearance 0.008”

Given that the centre main bearing feeds numbers 2 and 3 big ends, then an increase in flow to here is beneficial. The gallery can be opened out to 5/16” (7.9mm), to do this requires the removal of the distributor driveshaft bush and care should be taken upon reassembly to attain the correct distributor endfloat.

While the crankshaft is not particularly well supported, the use of main cap straps or even steel main caps is not required on a road going motor. What should be done however, is to bottom tap the main bolt holes and fit longer high tensile bolts (3.25” UHL), my preference being for socket headed bolts (with case hardened washers) which can be wire locked in place (in addition to using loctite). At the same time as addressing the mains, the big ends should be fitted with high tensile bolts (the originals should NEVER be re-used). Given the amount of 'monkey metal' fasteners being supplied these days, I suggest you use ARP bolts (which are stronger than the con rods) – a bit of a 'no brainer' really. Alternatively (for those in the UK) Ford Sierra Cosworth big end bolts can be used since they are a straight swap (and somewhat cheaper!). Similarly I use ARP head studs and flywheel bolts.

The crankshaft / flywheel / front pulley / clutch MUST be accurately balanced to help cut down on vibrations inducing crank flex (the stock factory balance is poor at best and is, I believe, a factor in shortening the life of the engine); a lightened flywheel is also of help here. Additionally I lighten the rods by polishing them down the beam (as well as removing the 'cup' at the little end). I then balance them end-to-end and overall to within 0.1g. If you are worried about con rod strength and unwilling to shell out ££££ on H-Section forged rods (qv later) then use the early TR5 rods since they are basically the same albeit stronger and lack the hole in the shank above the big end.

With respect to bearings, ideally a lead-indium type should be used since these will better resist the loads encountered than will reticular tin ones. Unfortunately Vandervell VP2 are no longer available for this engine. This leads us to some choices:

For 'hard' use it is possible to fit MGB big end bearings (original part no. AEB4512) at 0.010” undersize (for a standard crank). The crankshaft should be ground to 1.8665” – 1.867" (ie 8.5 thou). The outsize edge of the locating tang on the bearings needs to be filed down slightly to locate them correctly in the con rods. Additionally, since these bearings are wider than the originals, the fillet radius of the journals must be checked after grinding and modified as necessary.

Having done this, while Tri-Metal VP2 bearings are unavailable, the alternatives are:

AE GS2541LC, which is a Tri-Metal, sintered lead-copper bearing. This is essentially the same bearing as the Glacier Vandervell VPR91173LC but which uses a lead/tin/copper overlay as opposed to the lead indium in the old VP2 compound.
This is a high quality bearing piece able to withstand moderate to high loads

A better alternative is the Clevite 77 compound (part no. CB792P), which is made in the USA. This is another Tri-Metal design using a lead/tin/copper overlay, the difference being that it uses a cast copper/lead material (similar to the old VP2) and, hence, is about 20% - 30% tougher in its ability to withstand loads than is the GS2541LC.

A final alternative is to use ACL Duraglide 780 Tri-Metal heavy duty bearings (part no. 4B2250). These are essentially similar to the Clevite design.


If you don’t wish to go to the effort of fitting MGB bearings, and for a car that will see only normal / occasional track day use the expense is probably not worthwhile, then 'normal' Tri-Metal bearings to fit the big ends are available from King (part no. CR4403AM).

With regards to the main bearings having a VP2 like compound isn’t as critical however I still believe the best bearings available should be fitted. To this end I would suggest using King part no. MB341AM.

With regards to bearings made by King, while they are available from the manufacturer in sizes up to +60 thou in the USA, for those of us in the UK the sole supplier is 'County' under the brand name 'County Heavy Duty'; while the parts come in boxes marked 'King' they are actually stamped 'County'. Furthermore County have cornered the supply of these bearings and (for some unfathomable reason) do not supply in sizes greater than +20 thou.

Another worthwhile modification is to source an earlier style 'small bearing engine' camshaft and insert cam bearings into the block since in the 1493cc motor the cam runs direct in the block with no bearings.

These engines can also suffer oil feed problems to the rocker gear (although this is more the case on the earlier 1147cc motors) and there are a number of companies that will sell you an external rocker feed kit. Unfortunately ALL these kits are fundamentally flawed as they come, and lack adequate instructions as to their fitting.

EVERY kit I have seen uses a –3 hose with a banjo fitting to go into the oil gallery plug at the back of the head, and a 3/8" UNF female fitting that attaches to an adapter block that has a 1/8 NPTF male thread that screws into the main oil gallery beneath the distributor (the adapter block is there so that the oil pressure gauge line / pressure transmitter can be retained). A moment’s thought, given what I have said about oil feed to the centre main bearing, will show up just why this is a BAD idea. By connecting the rocker feed in this way you will INEVITABLY rob oil from the centre main, hence you will actually make your motor more likely to go pop! Additionally, with no restrictor, you will over-feed oil to the rockers causing problems with inlet valve stem oiling at low rpm (meaning your motor will both burn oil and be closer to causing detonation from the reduction in octane of the fuel/air charge!). Finally, merely fitting an external oil feed while the internal oilway to the cylinder head is active will cause cavitation in the oil galleries and all sorts of flow problems.

By far the best way to fit an external rocker feed is to firstly block off the vertical oilways in the block and head (use a tap and an 8mm grub screw in both block and head) and to take the feed from the main gallery at the rear of the block (opposite number 3 main) via the 5/16” UNF oilway plug tapping. To do this you will need a –2 to –3 male-male adapter to screw into the side of the block (the fact that this tapping is -2 means that you do not need a further restrictor).

Another problem often reported with the Triumph 4-pot is the tendency for the thrust washers to drop out on high mileage engines. This will rapidly result in wear to the sides of number 3 main bearing cap and a block and crank that are scrap. While you could silver pin the thrusts in place, this is really only of use on a race engine that undergoes routine teardowns and rebuilds since wear of the thrusts will mean the heads of the silver pins becoming proud and damaging the crank. For a road / occasional Track Day motor I wouldn’t bother, just check the thrusts every 40,000 miles or so.


With regards to forged cranks and con-rods:

Farndon engineering in the UK http://www.farndon.com/index.htm have supplied Triumph 1500 cranks in EN40B but the cost is horrendous (around 2-3000 GBP) and IMO too expensive for a road engine.

Additionally Carillo will supply forged H-Section con rods (at around 1000 GBP), but again these are pointless on a road engine. The reason being that a road going motor will never see the sort of rpm that requires such. The stock rods are good enough for power outputs upto around 120bhp, but in order to get this sort of figure you'd have a car that would be virtually undriveable on the street. Additionally you still run into the problems with the narrow big end bearings so you'd still have to go down the MGB route.
Deborah Evans

wow . thanks that has given me a hole new insite on the problem.. i am no armechaair mechanic . haha. we go threw some of the bearing problems at the john deere dealer i work at . i am a diesel tech. i have been working on my midget sence i was 14 . and i am 20 now . . and love every moment of it .

thanks yalll for all the help

Michael Koegel

Texas



p.s. o i have seen the ah spridget tuning books . do they include the 1500 in thos tuning guides ?


mck mike koegel

Hey Deb,

Awsome artical, But you failed to address one if not the most important points... How do you attach a 140 ounce 7-11 super gulp cup holder to the 1500 engine...LOL.

Prop....Deb always makes me so horny every time she talks engines .... What a Gal, Im SO in love.
Prop

Michael, YES including gearbox stuff and alloy parts you guys have never heard of.
Daniel Thirteen-Twelve

Michael,


David vizards bible and Danial Stapeltons super pro series of midget books are the only globel treasures that MUST be saved on dec. 21, 2012 when the world ends.

get your copys Of Danials work soon, with the hattie earth shake situation his books will be limited, no doulbt rioting will in sue shortly as these poor earth shake victiems strive to find a good replacement copy of Danials books that have been lost in the tragady.


Prop...Keeper of the midget flame
Prop

Where can I find the whole MGOC article you wrote Deborah? This is really intriguing!


Ron Koenig

Deborah, that's great information, thanks for sharing it with us.
Bill Young

Deborah, fantastic information. I thought I would share my experience with my 1500 as it my be of some interest. Purchased the car in 1986 with 50,000 miles on it. When I asked John Twist (University Motors) how to maintain the 1500 he stated to change the bottom end bearings every 45,000 miles and change the thrust washer and keep .003 - .004 end float on it. Don't go by the factory setting of .006 - .014. He also stated to change the oil at least once a season. We did the bearings at 50,000 then again at 95,000 (this only costs about $50). The engine has always had great oil pressure. Last winter I decided to pull the head off of the engine to see what things looked like since the engine now has 106,000 miles on it. I found some pitting on the tappets and on the cam. So, I kept tearing the engine down. There was no noticeable wear in the cylinder walls. I decided to go for a mild upgrade so I had the head ported and polished and milled 50 thousands off of it. I honed the cylinder walls and replaced the pistons with flat top pistons. Compression is now about 9.0 - 1. I replaced the cam with a mild cam from APT. I also replaced the timing chain. I did all this with the engine in the car since the bottom end didn't need anything. The car doesn't have an oil cooler on it but I do run a synthetic blend oil with high zinc content. The engine runs fantastic now and is a joy to drive.
tim swanson

Yes, great information!

Bought my 1500 last June with 76,000 on the odo...don't know the history of the car (bought it off a used car lot, rust free, all the pieces were there ,etc.).

Oil pressure is great...35psi @ hot idle, 75 to 80 psi @ 5000rpm hot...no knocking or rattle on cold start up, but put a dial indicator on the crank shaft nut & did the thrust washer test (10 times to be sure) & had readings of .010 to .014 inch free play.

Probably time for thrust washers, bearings?

Tim, how hard was it to do the work you did with the engine in place?

I've also been considering the flat top piston change over.

Been going through the brakes, suspension, electricals, etc.

Will soon turn my attention to the engine internals.

Just trying to build a reliable weekend cruiser.

Got too much time & money in it to stop now!

Dave

Dave Rhine

Memory loss being the second sign of old age it seems to me in my distance past thet there was someone that was installing a four piece thrust washer by doing machine work on the block and main bearing. This would allow much better control of the end play in the crankshaft.
Please remind me.
Sandy
SANDY SANDERS

Sandy -
I've heard of that, and it could certainly be done, but since the big end bearings are always due for changing at 40-50,000 miles, you just change the TW then. Especially if you keep your big foots off the clutch! A lot cheaper and easier than doing the TW machine work correctly and then having a rod out the side of the block as they do.

FRM
FR Millmore

Dave, yes it is time for a new set of thrust washers. It would have been easier to do the work with the engine out but I wasn't worth the time to take it out. Once you drop the oil pan and unbolt the rods, most of the work is done from the top anyway. It is a little tricky getting the crankshaft pulley off.

It is possible to machine the block to take four thrust washers but if you keep the endfloat tight you shouldn't have any issues.

Tim
tim swanson

This thread was discussed between 16/01/2010 and 31/01/2010

MG Midget and Sprite Technical index

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