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MG Midget and Sprite Technical - blown up 1275, rebuild qustions

well as I stateed in the gen sec. I blew the 1275 engine today...

Its in the lower end, my guess is a main or connecting rod bearing died, or the bolt holding connecting rod togather let go.(most likely)

it went really fast ....went from running smooth to trying to ventalite the block all in under a 1/4 mile...started with going up hill passing a truck at 3500rpm and started sounding like the muffler had come loose, then it started knocking and by the time I got around the truck and back on the shoulder it want from knocking to banging...and no warning whats so ever



So my question is, if the block is okay, How do I determine if I need a new crank and rods, or what condition should the crank be in to just polish and throw new rods and bearings in....should I get all new (used in great shape) rods and have shot peened or just replace out the one bad rod...(agian Im guessing at this point a rod went bad)....


thanks

prop
Prop

Prop

did you stop it?

or did it stop you?

if you stopped it you may only have lost the bearings rather than a rod

Still going to be a visit to the machine shop but may just be crank grind and bearings

[dont forget though this is the ideal time for you to spend a huge fortune inside the motor ;-) ]

in fact if you send me many thousands of dollars I will come and drink your beer whilst we both suck hollow teeth at the job to be done

[I can spare next thursday afternoon]

no seriously, it is unlikely to let you get away with new bearings without a regrind

If you can get the main bearing centre strapped (if it hasnt already been done) that would be a good use of the down time

Let us have pictures wont you

I'm hoping the damage is minimal for you Prop

good luck
Bill

Btw...

this is going to be a high performaance engine I have been planning for as winter time project, I was going to do it in 2 sections, build the head first with a nice spare head that I got, (big valves, hardened seats, rimflow wasted stems valves, bronse bushings, ported, the works) .... then do the lower end, slap the 2 togather, and done!

So NOW my thinking is this...not sure if this is a good idea or not....but shift my focas from the head to the lower end of the engine

pull the engine, rebuild the lower half with the new high performance pistons, camshaft, lifters, oil pump, ect. ect the whole lower end, "Then install the old current total stock head, (which is in good shape), cause I dont have the time, money, or parts right now to finish building the new high performace head, that way I can break in the enngine make sure everything is fine then install the new high performance head later this winter when I have I have it finally complteted


is this a good plan or a bad idea???...Id like to get the midget up and running soon, but just not ready for a complete total engine build right now....


Currently I only need ....pistions, valves, arp bolts, gaskets, seals, and bearings. Then I still got to finish building and modifying the carbs, make an intake manifold, do the mods to the head. then Im ready for the rebuild. I got everything else. including a great bunch of guys at a machine shop, that will be doint all the machine work

Any thoughts, ideas, past experiances, opinions both postive and negitive are welcome.

thanks guys

prop

Prop

Prop. You need to tear down the engine and perform a visual inspection of the parts. At that point, you will have a good idea if you need to take things like the con rods and crankshaft to the machine shop to have them perform an inspection.

If the parts look good on your visual inspection, a machine shop will have the tools and measuring devices to see if the parts are in tolerance and to crack inspect them. If the parts are obviously trashed, no need to spend the money on a machine shop inspection.

Each engine failure is different and you never know what you will find until you tear down the engine.

I have included a photo of my latest engine "blow up" which happened at 150 miles on a newly rebuilt engine. Please note, on the lower right hand corner, the new Moss connecting rod bolts.

Les


Les Bengtson

Les,
OUCH!!! That's gotta hurt!
Graham P 1330 Frogeye

thanks bill...

how about tuesday instead...lol

luckly I shut the motor down,,,the whole experiance lasted around 30 sec. no more the 45 sec. from the time I heard what sounded like the muffler comming loose to the turning off of the key when it was banging a way....like I said it was fast.

Still I wish or could have shut it down faster...dodging simi trucks and crossing 2 lanes of traffic getting to the shoulder while wondering whats going on at 75 mph...is a bit time consuming as well as shockingly distressful.


the RE-grind is whats bothering me the most, because its going to be pumping out around a 100 hp (agian Im guessing)...im not sure what a good comfortable re-grind amount would be, granted it wont be raced that much...more of a look what I did cool factor kind of thing...I was planning on doing the center stap as well

There are always cranks and rods on evil bay...but still thats a gamble as well...

Im suffering from a bit of chink as to the new situation as to how to know what a minimal stardard of re-grind would be for a high performannce engine or figuring out what the minamle amonut of allowed stress can be applied to deteremine if I should replace out all 4 connecting rods...

intresting huh!

I certianly dont want to rebuild it agian a year later...so id really like to do it right the 1st time instead of 4 times later...but dont want to kill a house fly with a shot gun at the oppisite end of the situation.


prop
Prop

go see your machine shop and see what oversized bearings they can get.

Good idea to get the bottom end done - crank, cam, oil pump, followers, flywheel etc and use your standard head until you can do the top end.

Get the engine apart and lets see what you've done. Get a mate round and it'll be in pieces on your workbench being photographed within 3 hours of him arriving.
Tarquin

HHhhmmm, im guessing a little JB weld will have that connecting rod and piston back 100% performance shape ...LOL

you are coreect Les,

what Im trying to do is get ahead of the curve a bit, and have all my ducks in a row, by haveing all the parts ready to go or knowing where I am going to get them, so I dont have to wait around, hoping something comes up that im looking for.....I figure if I know the minume toleraances, I can be looking out for that stuff now, so I can grab it if I need it later....

I keep my car is a storage building that I run my painting business out of...10 x 20...so space is a issue....cant have the car down for 2 - 3 months...so thats why my need for organisation is so curscial

When I make the move to build the bottom end, I want to do it in under 10 days....so alot of advance planning is a close secound to every thing else.


prop
Prop

Tarquin,

Are you telling me, that with Arie's help, I can have my midget back togather and running in almost no time...lol


Yeah...I knoww your correct, I guess ill get the pistons, arp bolt set, and conversion gasket set before, I yank it out....and track down some rods and crank on standby....then tear it down and get it to the machine shop, for bearing measurement...that way if i need the rods and crank, I can get those delivwred while we are waiting for the bearings...


thats not a bad Idea...that probable the best Idea for the situation Im in currently


looks like I definatly got to get a digital cam now for this new adventure.

prop
Prop

I would question if your block is damaged. If the rod bolt let loose and the rod broke, a lot goes on in a short time at 3500 RPM. You will be spending a lot of money to get 100HP with a questionable block. If the rod bearing spun and just chewed up the rod and crank journal, life is good. If you do look for a crank and rods on eBay, look for oldgreynorm. I have bought many items from him, including rods and never had a problem with the parts or the seller.
J Bubela

Prop, I think you might be best to strip the engine down before buying loads of bits as spares. You might be pleasantly surprised.

I'm sure someone over there will help you with crank & rods at short notice if you need them.

You can always keep the engine in the kitchen at home...
Tarquin

I'd have the crank checked at an engineering shop. If OK, install with fresh oiled main shalls torqued to spec, turn the crank over a couple of timesto check it doesn't bind. Take a look at the shells to verify with no marks. If OK, then you have a clear path for the rest of the rebuild.

A
Anthony

Prop do remember centre main bearing cap strap for extra rigidity

that will allow for more use of higher revs in safety

my very next engine mod, machining for this is not very expensive and can save on the price of the next crank

even if I don't have any other job done to it, it will be coming out for that

seeing the tacho showing 7k on change downs at the track days I've done has been a bit (A BIT???) alarming...


I dont think an oversize on the bearings (mains or big ends) will cause any loss of ability for the engine generally

some factory engines come/came off the track at one grind oversize some times, or at least they have been known to!!!

ps sorry I cannot make Tuesday this week
Bill

there is a 1275 rebuildable engine on ebay with 3 days left to go, for $400 ...i wonder if that might be a better option, just to eliminate any problems...

still I guess its just going to have to strip it down for a looksy...so I know what I got...

prop

http://cgi.ebay.com/ebaymotors/73-MG-MIDGET-WORKING-1275-ENGINE-TRANSMISSION_W0QQitemZ150295134214QQcmdZViewItem?hash=item150295134214&_trkparms=39%3A1%7C65%3A10%7C240%3A1318&_trksid=p4506.c0.m245


Prop

Prop:

I just checked the eBay link and then followed up on the seller's feedback - looks like this engine (or what is left of it...) came out of a 1974.

You might want to get the engine number from the ID plate on the block to confirm just what type of pig in a poke you might end up with...

Beats a stick in the eye!

I can't believe that you can't find 1 1275 closer to your part of The Woods..

Mike P.
Buffalo, NY
Mike P

IIRC the 1974 engines were rated best because of the bigger bottom end flange.
Bas Timmermans

"the 1974 engines were rated best"
So are the 1974 born boys!

ahum,

As a objective and completly neutrall person i think it just had to be said! LOL
Arie de Best

Prop,
Before you spend a lot on pistons and bearings get the block and crank to a machine shop for examination.
Shame to buy standard or +.10, then the shop tells you they need .20 to make it right.
Same w/ pistons. I went for +.20 from high comp "Cooper" type from APT.
Phil
Phil

THe spare engine is the way to go. With only 10 days for the car out of service, you really need to consider getting a second engine. Then you can put your blown engine on a stand in your shed with plenty of time to do it right. I'd recommend doing the engine rebuild SLOWLY - take your time, see what you need, don't buy anything till you take it apart. Slow and methodical will get you a great engine when you finish.

BC
B C Hamper

"""the 1974 engines were rated best"
So are the 1974 born boys!

ahum,

As a objective and completly neutrall person i think it just had to be said! LOL""



is that because you have a thicker bottom end flange Arie


it just had to be asked! LOL
Bill

Bill, there is something bigger but it aint my bottom! LOL



Allright this is still an open door for some of you jokers: is it the plate infront of your head, beer-belly, ego, nose/ears, hamroids and what ever you sicko's can come up with... LOL
Arie de Best

Ego?
Bas Timmermans

E do
Bill

E.L.O. ?
Arie de Best

ELO?
Elephantinely Large Orifice?
Extra Licking Optional?
Exceptionally Little Organ?
Tarquin

>>>>>>Bill, there is something bigger but it aint my bottom! LOL<<<<<<<<<<


Im not sure I know what you mean....is it what comes out of your bottom??? 8 ^ (


prop
Prop

The thick flange blocks are considered stronger, but they were not just on 1974 engines. The thin flange blocks were primarily on the early 1967 1275s (IIRC) and came with the best crankshafts. I seem to recall that these were really Cooper engines pressed into service while the "proper" 1275 engines were getting into production. I think the added strength of the thicker flange is a bit mythical...
David "couldn't find anything on it in Snopes, however" Lieb
David Lieb

This thread was discussed between 21/09/2008 and 23/09/2008

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