cross drilled crank

[902a]

As you know, there were two different cranks used in our boxer engines.
Some earlier Alfasud had the cross drilled version , later models then had a crank with straight shot oiling.

What do you think, is the best crank for racing? With an engine, that revs up to 8000 rpm..

Coss drilled crank below

Ali

[AlfaCorseChris]

I thought they did the straight drilling afterwards as an improvement.

I suppose it also depends on your oil pressure.
The straight holes were also significantly larger, werent they ?

[902a]

I thought they did the straight drilling afterwards as an improvement.

I suppose it also depends on your oil pressure.
The straight holes were also significantly larger, werent they ?

No, the straight drilled bores are not larger, but there is one bore less per journal.

So, is the later crank with straight drilled oil bores really an improvement..?
Or would be the earlier cross drilled crank the better one for racing..?

[Johnboy]

I would ask the Bls boys ,as there boxer revs around that level I be leave

[BS25]

Hi Ali,

We always used a cross drilled crank as a basis for our non-steel crank 8v engine (the one you now have the heads from). I would use 8000 rpm without an issue - obviously everything else was healthy. Keep an eye on big end bearing wear though, there hasn't been a competition suitable material for years. Other than the need to use more rpm reliably, another benefit to going to a steel crank was to take out the standard big end dimension so being able to use a bearing made from a race suited material. On the 8v we used to swap them after 4/5 races (typically 250 mins of running) - there was appreciable wear evident.

[PETROLHEAD]

Was that a modified crank, i.e. you had the crossdrill carried out on an otherwise stock crank,

or was it a crossdrilled crank as suggested by 902?

[902a]

Hi Bryan,

did you use a standard oil pump with 33 mm gears with this cross drilled crank?

I´m afraid, at very high rpms the pressure created by the standard oil pump is not strong enough to counteract the centrifugal force that is pulling the oil away from the rod journal feed hole.

And the higher your revs, the higher the centrifugal forces will be.

Swapping the big end bearings every 250 min means to swap them every two races. There are 15 laps with 20,8 Km each to go a race, so each race is about 312 Km..

Ali

[BS25]

Should have made that clear - it was a stock 1.7 crank that was subsequently cross drilled.

The oil pump we used then and now is a new 16v pump shimmed to increase the pressure. Not sure on the specific details on that one but I'll ask my Dad for more info tomorrow night.

[PETROLHEAD]

Hmm, interesting!

I'm very eager to hear more on that oil pump mod, i can only assume that means pretension on the relief valve?

The one thing that has escaped me to date though, is the use of 16v pumps only, to my knowledge the only justification i've heard is that the drive gear is deeper, and therefore more reliable, BUT, in the early sud and 8v motors, the oil pump gear only shows contact of around 75/80% of its driven surface anyway.

Is there another reason i'm missing?

hardened gear material? or just the fact that 16v should mean more youthful perhaps?

[KevJTD]

deeper gears, 33mm against 30mm, give more volume per given revolution. 10% more volume by the looks of it.
higher volume rather than a higher pressure.
the pressure relief valve can be altered with the springing to make the pressure higher before it starts to bypass the produced oil pressure which merely gets dumped back to the sump

that's what i think anyway

[902a]

Was that a modified crank, i.e. you had the crossdrill carried out on an otherwise stock crank,

or was it a crossdrilled crank as suggested by 902?

@ Shrew
Today I thought about your objection above..
And yes, your are absolutely right. There is a big difference in fact in crossdrilling a standard (not crossdrilled) crank and using an standard crossdrilled crank. I hope, you know, what I mean..
So two possibilities were now three..

Ali

[Veesix75]

Bryan - when using the standard crank in your 8v, what shells did you use?

In my class F spec car I fitted standard oem, and changed them every 4 or 5 races (on the advice of Tom)

However I was unsure if standard oem would withstand 8k rpm?

I want to change mine, and it is a std 1500 crank.

[PETROLHEAD]

@ Shrew
Today I thought about your objection above..
And yes, your are absolutely right. There is a big difference in fact in crossdrilling a standard (not crossdrilled) crank and using an standard crossdrilled crank.

Ali

Oooh, objection is a strong word Ali! lol!

Subject to clarification sounds more like it!


Yes, i know what you mean, which is why i asked.

a "Crossdrilled" stock crank would probably end up quite different to a crossdrilled alfa supplied designed crank.

Yes?

[902a]

Oooh, objection is a strong word Ali! lol!

Sorry for that..

a "Crossdrilled" stock crank would probably end up quite different to a crossdrilled alfa supplied designed crank.

Yes?

Yes, the crossdrilled stock crank is Version no.3. But which one is the best for racing? Who knows...?

[KevJTD]

a steel one

[BS25]

Definitely a steel racing crank is best, no doubt.

I've been in Lincoln and taken a few photos to help explain what we did on our non-steel cranks. We always used a stock 1.7 crank and had our cranks crossdrilled in a manner entirely different to the stock Alfa way!

The photos below shows one of our cranks. Looking at the left hand side of the crank, the standard Alfa drillings are those with the wire inserted. We left those unchanged, but crossdrilled each main and big end separately and then linked the main to the big end by drilling down through the web and picking up the crossdrilled holes. The ends of the drillings through the web were then tapped and plugged.

We use a new 16v oil pump, lap the pressure relief valve in carefully to ensure it seals and add a 1mm shim under the relief valve spring and also add restrictors in the block oilways to the cylinder heads to try and keep oil pressure back in the crank. The restrictors reduce the gallery size to 1mm.

The big end bearings were 105 series big end bearings as the material was better, but had to machine them down on each side as they are originally too wide. We would change them as a precaution after every 3rd race. We would also change crank thrust bearings at the same time. Mains would do a season. On the 16v we use Joe Gibbs XP6 race oil - its very good (but not cheap) - it wasn't available when we were running the 8v but we have run Ted's engine on it and will supply it for Simon's Trofeo. The technical advice we received on it would be that it definitely helps reduce wear.

Tim - the shells were certainly wear if you are using 8000 rpm - but also remember that if you are on standard rods then big end bolt life becomes a concern - as well as crank/rod material and age.

Hope that helps!

[902a]

Thanks a lot Bryan, very helpful..!!

Ali

[Veesix75]

Yes, many thanks Bryan.

Mine has Nord shells fitted currently, and I have an old set as a reference.

Is the machining simple to do?

And you know the next question, which bolts did you use on the std crank?

Thanks again.

[BS25]

Tim - the crank cross-drilling was very difficult and we struggled to find someone to do it - it cost approx £350 - we've not needed to have it done since 2010.

To be honest we wouldn't contemplate a high (ish) revving engine with standard rods/bolts - we've been using H rods for years - Arrow do the best. Naturally those rods are fitted with ARP bolts. Perhaps speak to Arrow about converting a standard set of rods to ARP bolts. I know it sounds OTT to be cautious about engine spec and sustained high revs though any failure tends to do catastrophic damage - taking expensive heads, pistons, etc with it. I know the Class F guys were using 7600 rpm all the time - but the more standard engines were a little more throw away back then. It's really a case of building reliability, unfortunately it's what makes these engines expensive as they are pretty much one-offs - but I can vouch for the reliability of a well specced and well built engine - as will Ted - he's never had a problem - dating back to 1989.

[Veesix75]

Wow, I certainly didn't use 7600 in class F.

Sorry, I meant machining for the shells, the old set look like they have had 1mm or so taken off each side. They are still wider than std boxer shells, 19mm I think, bit will need to remind myself.

Thanks again.

[902a]

which bolts did you use on the std crank?

I used ARP Bolts which are for a Renault Clio 16V (same thread M9x1) with standard rods. Since 2012 I´ve been using Arrow rods as well..

Ali

[BS25]

Wow, I certainly didn't use 7600 in class F.

Sorry, I meant machining for the shells, the old set look like they have had 1mm or so taken off each side. They are still wider than std boxer shells, 19mm I think, bit will need to remind myself.

Thanks again.

That must have been those running 16v engines - or nearly legal 8v!

I don't think machining the shells was too much of an issue, though luckily for me it was always something Dad sorted

[Veesix75]

Thanks Bryan.

And thanks Ali for the info on the Clio arp bolts.

[Ted27sud]

but I can vouch for the reliability of a well specced and well built engine - as will Ted - he's never had a problem - dating back to 1989.

Totally agree Bryan. The crank in my engine dates from 1989 and the rods from 1992. When Tom rebuilt it in 2011 all were checked for dimensions and wear and were proven to be perfect. I think that it's testament to fastidious maintenance by Tom, quality of original components and careful warmup procedures.

[Johnboy]

which bolts did you use on the std crank?

I used ARP Bolts which are for a Renault Clio 16V (same thread M9x1) with standard rods. Since 2012 I´ve been using Arrow rods as well..

Ali

Hi chaps
Are these the bolts you used?

[902a]

ARP 216-6301, yes..

[Johnboy]

Brilliant thanks

[Veesix75]

I assume those ARP bolts fit 8v also? Thanks Tim

[902a]

I assume those ARP bolts fit 8v also? Thanks Tim

I can´t say, if they fit 16V rods as I never used them, but 8V rods they fit for sure.
But 8V and 16V rod bolts should have same thread and length..

[Veesix75]

Thanks, I have an 8v.

Sorry for another question, what do you torque the ARP bolts up to when tightening them up?

I've used a Haynes manual to get torque setting for the standard bolts previously, would it be the same settings for the ARP bolts?