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MG MGA - Engine Scroll

My fellow motor heads! I removed my crankshaft tody to begin replacing my spun rod bearing. After analyzing the crank I noticed that there is hardly any scroll left. I'm sure this contributed to what I felt was excessive oil leaking. It does appear that the PO did rebuild the motor to a certain extent,(new oil pump, pistons,bearing, crank) Howerer I need to determine why the beasring spun and did the scroll get recently "damaged" or did the PO do a lousy job and installed an inferior crankshaft.
Comment welcomed!

WMR Bill

Here is the block were the sroll sits.

WMR Bill

I wanted to add on more pic of the crank sitting in the block. Notice the scroll touching the metal. Now I do have a new crank from a 1600 engine I plan to use to replace this 1500 crank, However, do I need be concerned with the surface on the block?

WMR Bill

Have you read the BMC Service Memorandum MG212 on Barney's site?
Some comments on scroll clearance.

Mick Anderson

I did. I think that pertains more to the "oil drain" from the rear jurnal. Although it does refer to to the clearence spec I need. I think my questions really refers more to (in plain terms) Is my block to boogered up? :)
WMR Bill

The scroll seal dimensions are here:

If the rear main bearing goes bad the scroll seal area on the crankshaft can touch the block and bearing cap, and all will be damaged. Building up the metal on the crank and re-machining the scroll groove could be more expensive than a good used crankshaft.

The block and bearing cap can be saved by line boring. The bearing caps will be shaved a bit (typically 0.010") to reduce the bore. Then the bearing cradles will be line bored a little higher (typically 0.005") to restore the original cradle bore size. In the process the scroll seal bore will also be restored, but pay attention that the scroll seal is not the same diameter as the bearing cradles. Line boring is relatively expensive, so a replacement block might be cheaper. But then you may get into cylinder boring and new pistons, so consider all in advance for cost comparison.

A cheaper and more expedient alternative is to install a custom built rubber rear seal. I do not recommend this for minor leaks, but it is quite useful for stopping the gusher resulting from a damaged scroll seal. See here:
Barney Gaylord

I did the conversion Barney mentions. I had a gusher alright. Looked like a coffee machine after a hard drive. I would lose 4 qts on a typical weekend run. It still leaks a bit. Several drops at each stop but it's minimal and much better than before. After the first run post seal I used about 1 qt in 700 miles, and some of that was from the leaky side covers and valve cover grommets.

If you decide to go this route, pay attention to Barney's great instructions especially the part about the RTV sealant!
Tom Baker

This thread was discussed between 23/07/2008 and 29/07/2008

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