RallyBob's Tricks For More CIH HP

[hrcollinsjr]

Originally Posted by RallyBob Another method of lightening a crank is via streamlining or 'teardropping' the counterweights... This method is cheaper in cash payout compared to paying a machine shop to perform either of the other mentioned techniques, since I can do it myself with a grinding disc rather than a large lathe. Bob

Bob,

I didn't realize one could just hand grind the counterweights by hand and have it rebalanced. I figured it had to be a little more precise than that. I may have to try it sometime. It is my understanding that the tear drop shaping of the counterweights is preferred over knife edging.

Harold

[RallyBob]

Found some pics on line of a 'streamlined' or 'teardropped' crankshaft counterweight. Looks like this was done on a CNC mill. Crankshaft looks to be a billet steel racing unit as well.

Bob

[RallyBob]

Originally Posted by hrcollinsjr Bob, I didn't realize one could just hand grind the counterweights by hand and have it rebalanced. I figured it had to be a little more precise than that. I may have to try it sometime. It is my understanding that the tear drop shaping of the counterweights is preferred over knife edging. Harold

The more precise you are with your layout and your grinding, the less work the machine-shop will have to re-balance the crank afterwards. I also weld- up the factory drilled balancing holes at the ends of the counterweights in order to reduce the chances of oil getting trapped in the holes and creating more windage. Takes more time, but it looks cleaner and hopefully works better.

Bob

[GTJIM]

Unlike V8 crankshafts 4-cylinder cranks do not have bob-weights attached when being balanced - the crank is just dynamically balanced bare. So this means that the counter-weights can be drastically lightened ... as long as it is done evenly on the up and the down counter weights.

A bit more engine rocking couples ensue ... but, Hey! ... it is not a smooth street cruiser you are driving.

Here is a good engine building web site that has excellent pics of a drastically knife-edged crank - which broke due to a machined stress riser rather than the actual lightening ....

Here: Engine Building

Lots to learn from this site! The counter-weights have been reshaped on a lathes by the look of it.

HTH

[jeff denton]

Thanks guys! Wow, I'm seeing some radical work there. Not quite the extent I'll be going to... Awesome!!
I found a 4-1/2" grinder wheel does most of the work, some places can't be reached so a carbide bit takes over. Then I ran a hand file over all the surfaces to smooth out the marks, then some 80 grit cloth. I didn't like those notches carved out of four of the arms, I smoothed out these areas and rounded out all sharp edges
Tip: tape up all the journals real good before you start any grinding, you don't want to nick it.
I have ten hours work into my crank so far, will do a bit of counterweight leading/trailing edge work and call it good.
Should a crank be shot-peened next?
Smokey says cranks must have the journals re-hard surfaced, a job overlooked by most. He says to even lightly polish the journal afterwards is a no no. Anyone ever heard of that?
I've done all this work to a crank with a hideous #1 rod journal. Hope it will grind out, otherwise this crank goes to Crankshaft Craftsmen for some welding and stretching. I hear a 2.2 stroke works pretty good these days...

[GTJIM]

Unless the crank has been 'Tufftrided' or 'Nitrided' there is no need to re-treat after polishing - either of those surface treatments should be done AFTER polishing as they are very thin layers of hardening.

Shot peening - on the other hand - is not done on the bearing surface but concentrates upon the fillet radii to compact and harden that high stress area. Needs to be done by a VERY competent shop though ... just bombarding a crank with steel shot is NOT 'shot peening' - it is much more technical than that!

The 2.2L stroke of 77.5mm is the "Sweet Spot" for Opel crankshafts giving more capacity without the penalty of rods hitting the lower cylinder bores or making a long-stroke 'Tractor Motor' out of the engine .... Go for It!!

Mind you 79.85mm might be better .... "Nah! It's STOCK ... 69.85 is a misprint!

[jeff denton]

Thanks Jim, I've heard of those treatments but don't understand them, I'll do some studying.
I was thinking the shot peening would put a finish on the non-journal areas of the crank that would LOOK like something non-razoo, just in case anybody ever got the honor and thrill of perusing my shaft. Gee, that sounded borderline obscene. Sorry.

[hrcollinsjr]

Originally Posted by GTJIM Shot peening - on the other hand - is not done on the bearing surface but concentrates upon the fillet radii to compact and harden that high stress area. Needs to be done by a VERY competent shop though ... just bombarding a crank with steel shot is NOT 'shot peening' - it is much more technical than that!

This needs to be done when reshaping the counterweights, correct? I know it does for polishing and lightening connecting rods.

Harold

[opelwasp]

Originally Posted by jeff denton Thanks Jim, I've heard of those treatments but don't understand them, I'll do some studying. I was thinking the shot peening would put a finish on the non-journal areas of the crank that would LOOK like something non-razoo, just in case anybody ever got the honor and thrill of perusing my shaft. Gee, that sounded borderline obscene. Sorry.

I would consider using the TiAlN very good lubricity and super hard.

Here are some informative links for PVD coatings:
http://www.guhring.com/downloads/CoatingS.pdf
Titanium Aluminum Nitride
BryCoat Titanium Nitride Coatings
Welcome to SECA - Surface Engineering Coating Association
Titanium Aluminum Nitride Coating: Pvd Suppliers from the PowerSourcing Directory - Distributors, manufacturers, and wholesalers of titanium aluminum nitride coating: pvd

[GTJIM]

Harold - the shot peening is done to strengthen the fillets in the shaft and is not necessarily done because of the machining done to lighten the shaft - standard shafts benefit just as much from correct shot peening.
In this case Jeff may be hoping for a little bit of disguise on the surfaces machined for lightening .....

There are many surface treatment that improve the surface hardness and lubricity of the bearing journals - pay your money and take your choice!

[hrcollinsjr]

Originally Posted by GTJIM Harold - the shot peening is done to strengthen the fillets in the shaft and is not necessarily done because of the machining done to lighten the shaft - standard shafts benefit just as much from correct shot peening.

Jim - It was my understanding that the lightening and polishing process removes the outside hardened surface and that the material was actually weakened. Shot peening is needed to reharden the surface. IIRC rods at least were lighter and stronger after polishing and shot peening because all surface imperfections that might be the start of a crack had been removed and the shot peening rehardened the surface as well as help with stress risers. Whew, hope no one knows what a run on sentence is!

Harold

[Paul]

Harold,

Shot peening doesn't harden the surface.... Its puts the surface stressess into compression (as opposed to tension or even neutral forces). Yes the polishing removes surface imperfections that could be the beginnings of a fatigue crack, which is a good thing. The act of polishing can remove material that would have been in compression, if the manufactring process (such as forging) had left the surface in compression. Then shot peening would have restored the fatigue strength, if the previous surface condition was in compression. Or the peening process would improve fatigue strength if the previous condition had not been in compression.

Fatigue life is improved because the compressive stressess must first be overcome before the surface can go into tension...

Clear as mud, right?

[RallyBob]

Considering the horsepower Dave's 2.5 litre engine was making, and the fact that the crankshaft started out as a billet piece, I personally think there was a defect in the crank before Dave bought it (second-hand). I've never even seen a stock Opel (forged) crank fail like that, so it seems to be an obscure failure. Who knows what the previous owner subjected the crankshaft to?

Bob

[jeff denton]

That is a huge bummer.
Interesting, he doesn't exactly give up a lot of info about how he got to 190 horsepower, other than compression ratio. By the way, it seems odd that 21 degrees ignition timing was pinging 98 octane fuel. Did he maybe have a lot more compression than he thought? Something seems strange there. Maybe some really excellent intake tract "supercharging"? No cam specs given, possibly some good amount of lift though.
I have heard that an engine that stopped real suddenly, like in a bad crash, has a ruined crankshaft. Not ruined as in noticeably, but stressed, cracked internally, ready to fail if used again.
I'm getting more and more nervous about using old (even meticulously reconditioned) parts.
Where do we get our new billet cranks these days? I mean a good one, not a cheap wanna be crank. If money was a serious problem I wouldn't have an Opel, that's for sure. A serious problem would be blowing up an expensive engine because one part was too cheap!

[RallyBob]

Originally Posted by jeff denton That is a huge bummer. Interesting, he doesn't exactly give up a lot of info about how he got to 190 horsepower, other than compression ratio. By the way, it seems odd that 21 degrees ignition timing was pinging 98 octane fuel. Did he maybe have a lot more compression than he thought?

Jeff, if you check out the rest of Dave's site, he gives full specs on the engine, including the camshaft specs. My opinion on the pinging...the cam is far too small for the engine displacement and the compression ratio, so the VE is extremely high at mid-rpms.

I've seen stock Opel engines ping badly with 8.5:1 compression, and I've had over 11:0 compression engines NOT ping on the same octane fuel because of a cam chang. It's all about the entire package: cam specs, cam timing, port volumes and velocity, induction lengths, exhaust tuning, etc.

Bob

[GoinManta]

I have two (or maybe three) 1.5L heads and an early 1.9L if anyone wants one..