MG-Cars.info

Welcome to our Site for MG, Triumph and Austin-Healey Car Information.

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG Midget and Sprite Technical - 1275 end float question

Hi Gang - not been on for a while and in fact chose lockdown 3 to rebuild the engine. After a long wait it is now back with me and plus 20 thou, so 1293 cc. I go to fit the original crank, which spins nicely, but the new thrust washers really jam things up. I fit the originals, which to be fair are in great order, and the crank resumes spinning nicely. However there is no detectable end float, which IIRC should be 4 thou min.
Have i overlooked something ? is my memory right on the end float required ? if so its a surface grinding job i assume for the thrusts to give me what i need.
Over to you lot. . .
P Bentley

i should have mentioned the block was changed from my original over bored block, back to a standard block.
whoops
P Bentley

My thinking is the blocks are ground pretty accurately, so swapping shouldn't remove the endfloat completely.

If the new thrusts lock the crank solid, that suggests to me that they are oversize. They may be marked as standard, but these days, you are well advised to double check by measurement. --- Assuming they are new standard size, and you haven't been sent, or bought oversize by mistake of course.

The front washers take the push. The rears do very little. I've swapped fronts to rear and rear to front before, if not having the thrust faces ground on the crank.

If the thrust faces on the crank have been ground, the machine shop used to provide the thrusts, or at least mark your ticket to tell you what sizes you need.

anamnesis

I’d start by doing a lot of measurements and checks. Compare the thickness of the thrusts, old and new. Measure the end float with the old thrusts, preferably with a DTI.

If you still have the old block try and compare the thickness of the thrust faces and see if there is any difference to the new one.

I’d also check that the centre main cap is definitely the right one for the block and that the dowels are tight. Bolt it on without the shells or thrusts and make sure the joining faces are perfect.

I’m not saying that any this will help or change anything but it might give a clue as to what is wrong and eliminate a few things.
John Payne

I don't know how relevant this is but when I had a crank reground and fitted into a different block, the machine shop line-bored the block and bearing caps.
GuyW

Perhaps check the crankshaft for burrs on the web shoulders. I got caught out with that once on a Pinto engine after a big end bearing broke up.
Unlikely but possible. Maybe....
Greybeard

thanks guys - will report back
P Bentley

PB
A std. thrust washer is .092" thick ,if that helps
Are you measuring the endfloat dry--you are measuring the oil clearance so needs to be dry
If it spins freely with the original washers it must have measurable clearance
When you put it together to measure up, get yourself a block of wood and give the crank a bit of a tap in both directions to just make sure the thrusts are settled in place
Std spec is .002"-.003"
Racers tend to like them out to .003"-.005" for some reason that's beyond me, I like them tight like .0015"-.002"
There's nothing wrong with mix and matching to get a result with say, std on one side and OS on the other--and contrary to what An. said the main thrust is taken on the rear washers not the front
What part number was on your new thrusts/packet

willy
William Revit

Ha ha. Ar*e about face. I wondered when someone would correct me re front/rear thrusts. I missed my edit window and figured I might as well leave my error in place for correction. Only one person spotted it? ; Or at least mentioned it. 😉
anamnesis

This thread was discussed between 08/06/2021 and 09/06/2021

MG Midget and Sprite Technical index

This thread is from the archives. Join the live MG Midget and Sprite Technical BBS now