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MG MGA - Con rod interchangability
|The MGA came with the 1500, 1588 & 1622cc engines, also here in Australia there is the 1620cc engine as fitted to the Lancer and of course the early MGB 1800cc three bearing engine.|
What I'm looking for is the interchangability of con rods.. I know there is a difference in little end sizes 0.685" for the 1500 and the 1588 engines and 0.750" for the 1622 and 1800 units. What is fitted to the 1620 engine and do the B/E journal sizes and over all rod lengths vary...? Plus do the B/E offsets vary..?
Many thanks in anticipation..
|M T Boldry|
|It is my understanding that the Australian 1620 engine is essentially a 1588 engine bored out to 3-inch piston size to make 1622-cc (and has "1620" cast on side of the block). It uses the smaller valve "15" head (like the 1500/1600 engines) and the dished pistons to match. Pretty sure it also uses the 1500/1600 type crankshaft (smaller main bearings) and the 1500/1600 type connecting rods (smaller wrist pin). The pistons then will be unique to the 1620 engine with 3-inch basic diameter, dished top and small wrist pin. The rest of the internal parts should be interchangeable with the 1500-1600 engines.|
Since I've never had my hands on a 1620 engine this is all second had information, so I'm certainly open to correction if I'm wrong.
|Correction to my prior message. All MGA 1500, 1600, 1622 and 1620 engine have same diameter main and rod bearings.|
The 1622 engine has different crankshaft with narrower center main bearing to allow thicker webs on teh crankshaft, and also different con-rods with larger floating wrist pin. The 1622 crankshaft can be used in the other engines if the center main bearing cradle is machined narrower to match the 1622 crankshaft center journal and thrust surfaces.
|The 1489/1588 rods are interchangeable with each other, as are the 1622/1798, always assuming checking for proper weight/balance.|
|And to add to Bills comment,be very careful and check the width of the big end. When a rod is rebuilt they split the cap, machine the parting surface.It is the cap is torqued and the inside diamater is remachined to the correct diamater.Then they machine the sides of the big end to clean them up.|
The reason I bring this up is I had them done on mine and the crank reground. By the time they were done I had anywhere from .036 to .040 rod to crank side clearance,factory says .008 to .012. You just don't know how many times the engine has been worked on.Too large a clearance causes a loud knocking when running a constant speed,accellerating or coasting no noise. In the end John Twist was able to help me out. I was able to get rods from him that seemed never to have been machined. Could never find a spec on big end width but was able to find ones in the range of 1.213 to 1.218 compaired to mine that were 1.195 to 1.200. Cranks were all over also 1.243 to 1.232. Got another but it was no help either 1.225 to 1.233 so 2 measurements were still over by .005 to .010. Ended up having a engine shop used and recommended by John to weld up my original crank to match my rods and get them back to .009. Been running since '95 with no problems. Sorry for the long post.
This thread was discussed between 03/07/2012 and 08/07/2012
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