33 replies to this topic

[A-Cell]

Nitriding or tuftriding heat treatment can strengthen a crankshaft.

[minilee94]

Okay but I don't want to keep my crank standard i want to improve it some how as my mate has kept his standard and it failed recently badly and i don't want that to happen to me

[A-Cell]

EN40B nitrided crank if you don't want it breaking, but mega expensive.

[TimmyG]

Okay but I don't want to keep my crank standard i want to improve it some how as my mate has kept his standard and it failed recently badly and i don't want that to happen to me

Having your crank 'bladed' or 'knife-edged' is unlikely to make it stronger. In fact making a sharp edge is more likey to make it weaker. What does make it stronger is stress relieving, which is basically using a sanding wheel/file whatever abrasive to clean the surface of the steel up until its smooth and any sharp edges rounded-off so there's no stress risers to start a crack. Once you do this you will then have to have it balanced again as material will have been removed.
Incidently blading/knife edging removes metal from the counterbalancer web of the crank, of which i believe there is insufficient to start with. 'Wedging' on the other hand removes material from the big-end journal end thereby improving counterbalancing (and therefore smoothness of running) whilst also lightening the crank.

So basically its free to make your crank stronger, as long as your getting it balanced anyway!

Edited by TimmyG, 08 January 2013 - 09:28 PM.

[minilee94]

So do you guys think i should have it heat treated , regrind but i still dont know if to have it x drilled instead of the other things what you think

[Cooperman]

You really don't need to do anything other than a full dynamic balance and a centre main strap to get the 6700 rpm you'll need to fully use a 286 cam.
Just make sure the crank is properly machined with good fillet radii in the journal corners. Having the corner radii too small is the main cause of crank failure.
You might want to re-think the SC drop gears if it's a road car. They are so noisy that you will need ear plugs on road journeys and are designed for competition use where a crash helmet is worn. They will cause hearing damage. I wish I had never fitted them to my rally 'S' and next bre-build they are coming out!

[minilee94]

to be honest cooper man i dont mind the noise the car wont e used loads and loads so won't be in the car too long and okay i just dont know what mods to do to the crank i just want a straight forward awnser on whats good to do to a crank

And I don't know 100% on cam yet

And a center main strap will be fitted

[Cooperman]

The A+ crank is stronger than the pre-A+ due to the improved corner radius design of the journals. Tuftriding doesn't necessarily make the crank stronger, it just makes the surface more durable. For a 286 cam where 6700 rpm will be used cross-drilling would be a good idea to ensure good oil feed at those high rpm's. The 286 is a rally cam really meaning that for best performance the revs need to be kept between 5000 and 600. If those sort of revs are not going to be used a lot of the time it's better having a 266 and with a 1380 the advantage is mainly better low- to mid-range torque and thus the need for any crank treatment reduces. The ley to the performance of a 1380 is in the head as it needs to be really well-flowed to release the performance.
So for a high-revving crank it's the journal corner radii and the balancing which are most important.
Edited to add that I do have an EN40B 1275 'S' crank for sale completely original and never re-ground. It's cross-drilled and nitrided as standard and it's ready to fit after balancing with flywheel and front pulley. It can come complete with the required 'S' rods as well. If interested PM me.

Edited by Cooperman, 19 January 2013 - 09:28 PM.

[minilee94]

Pm'd cooperman

[Gr4h4m]

You really don't need to do anything other than a full dynamic balance and a centre main strap to get the 6700 rpm you'll need to fully use a 286 cam.
Just make sure the crank is properly machined with good fillet radii in the journal corners. Having the corner radii too small is the main cause of crank failure.
You might want to re-think the SC drop gears if it's a road car. They are so noisy that you will need ear plugs on road journeys and are designed for competition use where a crash helmet is worn. They will cause hearing damage. I wish I had never fitted them to my rally 'S' and next bre-build they are coming out!

I'm not convinced on straps, without line boring and a lot seems to depend on who machines the cap and bar. They must be perfect. By the time you have done all this a 4 bolt cap must be the best option?

[Cooperman]

You really don't need to do anything other than a full dynamic balance and a centre main strap to get the 6700 rpm you'll need to fully use a 286 cam.
Just make sure the crank is properly machined with good fillet radii in the journal corners. Having the corner radii too small is the main cause of crank failure.
You might want to re-think the SC drop gears if it's a road car. They are so noisy that you will need ear plugs on road journeys and are designed for competition use where a crash helmet is worn. They will cause hearing damage. I wish I had never fitted them to my rally 'S' and next bre-build they are coming out!

I'm not convinced on straps, without line boring and a lot seems to depend on who machines the cap and bar. They must be perfect. By the time you have done all this a 4 bolt cap must be the best option?

Yes, for really high revs a 4-bolt high quality steel cap is absolutely ideal. For up to around 7000 rpm just a centre-main strap will help to avoid cap distoration so long as the cap is ground flat and the replacement bolts are very high tensile steel. Cap distortion and eventual metal fatigue is an issue with standard main caps and anything which helps reduce this is an advantage and will help the centre main bearing to last a bit longer as well. The problem with oil pressure at the centre main is that it has to go to lubricate two big ends, rather than just the single one as front & rear mains do, and there has to sufficient flow there to feed the thrust bearings. Plus the centre main will always tend to distort more than the end ones.

[Gr4h4m]

You really don't need to do anything other than a full dynamic balance and a centre main strap to get the 6700 rpm you'll need to fully use a 286 cam.
Just make sure the crank is properly machined with good fillet radii in the journal corners. Having the corner radii too small is the main cause of crank failure.
You might want to re-think the SC drop gears if it's a road car. They are so noisy that you will need ear plugs on road journeys and are designed for competition use where a crash helmet is worn. They will cause hearing damage. I wish I had never fitted them to my rally 'S' and next bre-build they are coming out!

I'm not convinced on straps, without line boring and a lot seems to depend on who machines the cap and bar. They must be perfect. By the time you have done all this a 4 bolt cap must be the best option?

Yes, for really high revs a 4-bolt high quality steel cap is absolutely ideal. For up to around 7000 rpm just a centre-main strap will help to avoid cap distoration so long as the cap is ground flat and the replacement bolts are very high tensile steel. Cap distortion and eventual metal fatigue is an issue with standard main caps and anything which helps reduce this is an advantage and will help the centre main bearing to last a bit longer as well. The problem with oil pressure at the centre main is that it has to go to lubricate two big ends, rather than just the single one as front & rear mains do, and there has to sufficient flow there to feed the thrust bearings. Plus the centre main will always tend to distort more than the end ones.

I understand the theory I just wonder if the strap method can also cause the cap to change shape and nip up the bearing a little. I have seen some reports where It was critical the orientation of the strap when building the enigne.
I'm starting to believe that some of these mods need to be completed perfectly or they cause more issues than they solve?

I don't know I'm only starting to build my first engine, just what I have found from reading? I'm still undecided if I should strap or not....

Edited by Gr4h4m, 21 January 2013 - 10:20 PM.

[Cooperman]

I was asked to take a look at an engine which a 'friend of a friend' was buildinh. He had fitted a centre strap amnd then the crank would not turn smoothly. I discovered that years ago there was an articcle which advocatred leaving a 0.003" 'step' at each end of tne cap when finally grinding it to allow a bit of 'pinch-down'. This was distorting the cap at the correct torque and 'pinching-down' on the bearing shell & hence the crank journal. After getting the cap ground accurately flat the strap was fitted and all was well.
On race engines a 4-bolt line-honed steel cap is much better, but a bit 'overkill' for a road engine revving at not too much over 7000 rpm with a fully balanced bottom end.

[Gr4h4m]

I'm thinkng of revving to 6500 and 6800 to gear change. I might strap.. need to decide soon

Edited by Gr4h4m, 21 January 2013 - 10:19 PM.

[Cooperman]

Many have used a centre strap over the years with good results. As you said earlier, it needs to be done properly by surface grinding rather than just milling as a smooth surface parallel with the base face is vital.