Engine and Transmission Tech

Hi guys,

It’s probably been asked a million times before so please bear with me.
I have a 300 engine that I’m going to rob the crank and other bits and bobs from and I want to fit it into a late large journal cross bolted block.
Has anyone actually done this with first hand experience, will the crank fit without modification, I’m going to use chevy rods and I have a set of forged pistons,
I’ve read various conflicting articles so I’m looking for some first hand knowledge.
Also, has anyone successfully fitted a 340 crank into a large mains rover block (after reducing the crank mains) or is that just too much stroke for a rover block.

Any info greatly received

Jeff 👍🏼

Jeff, the swing of the 340 crank is going to cause some trouble. The pan rails are narrower on the Rover than on the 300/340, you'd have to use a short rod and put the piston pin very close to the ring package and might have to use a small diameter pin but I *think* you can do it without having the pin bore intersect the oil ring land. Others have looked at it though and I believe the pan rails are going to be the real issue. That and the piston skirts. Then you'd have a short rod engine which puts extra stresses on the cylinder walls and the crank.

However, the 340/350 crank will fit in your 300 block just fine after the mains are cut down and makes a very fine engine that only weighs about 50lbs more than the Rover. The iron block handles the extra power much better and the MGB won't be affected by the weight.

Why build a Dixie cup when you can just as easily do an endurance motor?

Jim

I would offset grind the Rover 4.6 crank vs using the 300 crank, if you are after more stroke & want to use a Rover block.

Like Jim said, using the 300 iron block is better

Carl, had to ask being a newbie plus this forum is blowing me away vs regular "can't get answers" LR forums.
How much added stroke is gained offset grinding the 4.6 crank plus what about the journal diameters, what will they end up at in diameter?
Unless a welded up crank then ground down (not a good idea if welding a cast crank vs steel) as a stroker the journals would have to be much smaller also thinking a weaker crank.
THX. 95 D1 5 spd w/4.6, chipped plus other minor little tricks still legally passing Kalifornia smog tests. Minor item changes back to normal running conditions post test......~~=o&o>.......

4.6 crank has 2.185" rod journals where as earlier cranks have 2.000" pins. You can offset gring the 4.6 crank to 2.000" pin size and theoretically you can gain 0,185" extra stroke. In real life a bit less since you need to make sure that the pin is perfectly round. The actual stroke would be just over 86 mm (4.6 std stroke is 82 mm). John Eales in UK is selling large mains cranks with 86.36 mm stroke.

I have a 4.6 based stroker project with 91 mm stroke crank, SBC 6.000" rods and stroker pistons. I hit a speed bump with the dummy assembly: pistons sticking out of the block 60 thou. I knew that this would happen but was not expecting that much. The decks of the block had been machined in the past. No biggie if you could machine the pistons but they are stroker pistons with about 0.25" from top to 1st comp ring. That would leave marginal amount of material. This engine will have Wildcat heads with 1.94 and 1.60 valves so most likely valve reliefs will be needed. Valve pockets and lowered pistons means that there is a risk of machining the valve reliefs into the ring groove. Not ideal :-)

What I want to point out that increasing the stroke you will affect the rest of the package. Longer stroke may require longer rods, definitely shorter pistons and so on. Easiest would be buying a complete package, saves a lot of headache.

My options were either sourcing a new block (not easy), sourcing new pistons and reboring the block (doable but expensive) or finding shorter rods. Since the pin size is 2.000" the shorter rod option would be 5.850". That would leave pistons down in the bore some 80-90 thou which basically is not an option at all. I stumbled on 5.950 SBC rods but these are for 2.100" pin. Luckily there are specific 2.100 to 2.00 rod bearings so I bought these rods and bearings. Not so simple though, my crank is TVR stroker crank and for some very strange reason these engines have very narrow rods. I had to machine 90 thou from both sides of the rods. The bearings need to be narrowed as well. I have access to a lathe so maching was free. If you need to source it outside that is an extra cost again. I did a dummy build last weekend and literally hit another issue. The physically larger rod big end meant that two rod bolts hit the block and the crank would not rotate around. The rod bolts hit the oil gallery at lower RH side of the block. Smaller 6.000 rods cleared the casting. Some very nervous relief grinding fixed the issue. This is not the location where you would want to grind thru the casting.