M20 B3x Naturally Aspirated Stroker build past, present and future

[BUDNUNTA]

When you made the crank spacer, did you use the 24v boss and machine it down?

Do you think that crank seal surface should be hardened?

[digger]

Really looking forward to seeing how the roller rockers and cam affect engine performance. It would be very interesting to see a comparison between two standard b25 engines with the only difference being the roller rocker cam setup. I even wonder if stroking beyond 81mm is worth the extra cost and effort if the most sufficient gains are from head/valve train improvements? Maybe just depends on your wallet, what you have access to, and what you'd be satisfied with?

to be honest you wont know for sure what effect that they have as you only see the result of the entire system.

the simulations i ran showed that for the 3.3L the same duration the RHD cam is worth about 15-20 hp due to the more area under the lift curve compared to an off the shelf cam designed for the OE rockers. it delays when the torque starts falling over so it makes more topend but does not negatively influence the torque at the bottom end either.

The simulations showed the same gains would not be realisedon a smaller engine as a smaller engine just doesn't need as much lift as a big stroker...

As i recall the original motivation for Rama was for the roller design to be more durable when you move to aggressive cams as some of the aftermarket stuff was rubbish and the pads were wearing excessively.

[E30 Wagen]

Really looking forward to seeing how the roller rockers and cam affect engine performance. It would be very interesting to see a comparison between two standard b25 engines with the only difference being the roller rocker cam setup. I even wonder if stroking beyond 81mm is worth the extra cost and effort if the most sufficient gains are from head/valve train improvements? Maybe just depends on your wallet, what you have access to, and what you'd be satisfied with?

[digger]

l will be having mine replaced. i have a few sets of spares. even if parts go NLA any engine builder/machine shop worth their salt will be able to buy some material and machine up their own

[ForcedFirebird]

It's not an overly difficult procedure to do the shaft bearings, not sure what that whole "let's hide part numbers" thing was about. BMW should have just treated them like standard pushrod cam bearings. No reason to have multiple sized shafts to fit the block, rather than have a tolerance like the cranks do. Ultimately, the m20's are just another engine in my eyes, shouldn't have over-complicated things from the get-go.

[digger]

My block for the build has 120k on it and the leading bearing looks partly fatigued bits flaked away etc but that may be damage post tear down idk

[nando]

That's awesome! Half these new kids wouldn't even know what the intermediate shaft is. :p

Ok, a little confession. I never replaced the IM bearings of my M20 stroker. When I had the block tanked, I packed the bearings with grease and left an old shaft in there, and told them not to leave it in the hot tank for too long. Also, the block has something like 300,000 miles on it.. original bearings. I wonder what they look like now, lol...

oh, there are little washers/needle bearings for the shaft that drives the oil pump. I have an extra set laying around if somebody is desperate. :p

[digger]

There was no need to goto the extreme of a tool steel. Some of those steels are very notch sensitive.

[ForcedFirebird]

To add..I have personally machined 4340, it's ratjer soft prior to hear treat. Straw color, dipped in carbonated oil, a file couldn't scratch it. Snapped like a pencil after we hobbed the gears. A & D tool steel in the raw, hardened, then ground took carbide to re-machine.

Perhaps it's too hard/brittle for an oil pump drive?

[ForcedFirebird]

If it were so easy, it would be common. Thanks again for the insight, Digger.

Why not treat it like a tool? Use something like D1, heat treat, harden, then grind? Wouldn't be far off from a HSS drill/mill

[digger]

Plain bearing journals are hardened to stop the journal being damaged if you get crap through the engine, the bearing fails or the film gets compromised to limit the damage that occurs, ‘normally’ its riding on a film and not required. I've seen many BMW engines with crapped rod bearings haven’t need a crank regrind (have seen others that do depending how severe failure is) it seemed like a good option.

The lip seal providers recommend (depending on brand) a HRC 35 for regular seals or 45 HRC for higher speed shafts or 55 for the PTFE seals. I don’t want the seal to wear a groove prematurely so seems like a good option. This should be noted for those wanting an oil seal sleeve for the stroker cranks when using in an m20 engine they need to be good quality steel to last a long time

Heat treatment to increase hardness increases the fatigue life though that’s not why I did it. Hardness is directly related to UTS which forms a large part of the endurance limit. Nominally the endurance limit is ~50% UTS then there are several knock down factors e.g. surface finish, loading, size, reliability factor and stress concentration and so forth.

It’s a modified “4340” material.

[LJ851]

It's a plain journal bearing and seals don't need hardened surfaces to run on. If it were a rolling element bearing, it would need to be hardened.

How did you heat treat it? Hardening can hurt fatigue life, depending on other factors.

I @$$ume you had at least the necked shank shot peened.

What steel did you go with? 4340?

What? Why are all plain bearing crankshafts hardened if they don't need it ?

[The Dark Side of Will]

Its heat treated because the journals , the oil seal surface and the press fit.

It's a plain journal bearing and seals don't need hardened surfaces to run on. If it were a rolling element bearing, it would need to be hardened.

How did you heat treat it? Hardening can hurt fatigue life, depending on other factors.

I @$$ume you had at least the necked shank shot peened.

What steel did you go with? 4340?

[LJ851]

Very Very Nice, digger !

[digger]

An important piece to the puzzle finished. I needed a custom intermediate shaft to clear the big 93.8mm crank as even with a nice aftermarket slim rod it fouls alot.

Most people know the intermediate shaft drives the oil pump, but it is also an idler shaft and as such carries the timing belt tension and loads to drive the valve train which are cantilevered off the end. This is the reason it is so large in comparison to the oil pump shaft. if you do some load calculations and stress analysis and estimate fatigue life you cant just hack into it and expect it to be trouble free

If you machine the stock ones down too much you can cut through the heat treat and end up with flimsy shitty cast iron of sorts so didn't want to risk it. Fortunately with the 89.6 mm shaft it needs minimal material removal so most don't encounter this. i did however get told by someone who lightened one to reduce rotating weight that it failed and that it is indeed hollow to get oil to the inner bearing.

Those with engineering back ground will know what a bending moment diagram is and be aware that bending stress is proportional to (D^3-d^3) and stiffness is (D^4-d^4). So if you have say an 18 mm shaft and neck it to say 14 mm the stress goes up x 2.12 and fatigue life reduces x 10.

Knowing this i also tried to minimize the amount of material removed so that I didn't make it too flexible which might cause the intermediate shaft bearings to crap out too soon. The reason they can crap out is as the shaft bends the edge of the bearing gets very high local pressures and improper lubrication and I’ve seen some blocks where the front bearing has deteriorated.

To address all this I got the shaft made from high tensile steel bar and had it heat treated, plus i designed it with very low stress concentrations in the areas I modified so i didn't introduce any issues.

Since i had no drawings to start with i had to do my own so onto designing one I destroyed a couple of old shafts to get the gear off to use on mine (press fit) and the oil gallery plug as well as measure some important parts like the oil gallery hole size etc

I measured every dimension in fine detail and then 3D modeled in CAD with full detailed drawings including dimensions, tolerances, surface finishing requirements and heat treat. Its heat treated because the journals , the oil seal surface and the press fit.

I got one 3D printed to check clearance before going to production.







did a test fit into the block i will be using and it glides nice and smooth

it may seem like a simple part but even being an Engineer i realised there is a lot more that goes into it than at first glance and i learnt a lot through the research i did in designing and understanding what specs to use etc.