Shortnose Crank Issue

corners · Postby **corners** » Sun Feb 22, 2009 4:18 pm

Hey All

Well after pulling apart the car on saturday is appears I have the shortnose crank issue again.

Just wondering if anyone has heard of a method where the crank is welded and then respun and balanced??

Cheers
Jaron

JBT · Postby **JBT** » Sun Feb 22, 2009 6:34 pm

I think a good used engine is cheaper in the long run.

tbro · Postby **tbro** » Sun Feb 22, 2009 7:19 pm

Jaron

Spray welding on crankshafts is only really successful if done on a tapered or plain nose, despite what most machine shops will tell you.

If a keyway is used then the success rate is very poor, 100% failure rate on every crank I had done, some last 5 mins, some 6mths.

Really only a temp measure if you are desperate.
Price up a second hand motor, you and your wallet will be better off in the long run..

Terry

corners · Postby **corners** » Sun Feb 22, 2009 9:27 pm

Bex037 wrote:If you're into rebuilding engines, there was a Mazda fix called the "Long Nose Crank". That is, new crankshaft. I don't know whether Mazda still support the mod or whether its too expensive. If you check it out, let me know; I've got a 1990 with short nose crank but no sign of any problems

The issue can occur at anytime though.

Depending on many factors mainly who worked on the timing sprocket last and how it was put back in

corners · Postby **corners** » Mon Feb 23, 2009 1:43 pm

Thanks for the other suggestions.

Has anyone attempted the 1.8 upgrade themselves?

From reading stuff there is very little that has to be changed apart from the stuff included in the flyinmiata kit.

Any feedback appareciated.

Cheers
Jaron

Postby **Okibi** » Mon Feb 23, 2009 2:29 pm

W.A. members have found it's not worth trying to run the 1.8 on the factory 1.6 ECU, factor in something like a plug n play wolf/megasquirt. Upgrade to the 1.8, ditch the AFM and make even MORE POWER ... it's win win.

corners · Postby **corners** » Mon Feb 23, 2009 2:48 pm

Okibi wrote:W.A. members have found it's not worth trying to run the 1.8 on the factory 1.6 ECU, factor in something like a plug n play wolf/megasquirt. Upgrade to the 1.8, ditch the AFM and make even MORE POWER ... it's win win.

Oh really? What kinda issues arise? Do you know?

Postby **Okibi** » Mon Feb 23, 2009 5:49 pm

I think it was getting the fuel mix right, Les would know better.

Postby **mx52nv** » Mon Feb 23, 2009 6:31 pm

Specific to club members Robyn and Vaughn's 1989 NA6CE, which Vaughn (mechanical engineer) did the 1.8 conversion himself after making sure he read up on the information about this on Miata.net. After completing the conversion, the car just did not have any torque after about 5,000 rpms and no matter what he did, it just couldn't pull after that rpm range. When it was brought it to the old workshop, we put it on the dyno straight away to see what it was doing exactly and to get an A/R reading.

The dyno told the story as the 1.8 injectors were just not putting fuel in after 5,000 rpm. Since we had a Plug 'n' Play Wolf for NA6s, we quickly swapped ECUs and with our basic tune, the car was working fine with power all the way to 7200rpm. We put it down to the 1.6 factory ECU not being able to control 1.8 injectors completely. May work for some but not for Robyn and Vaughn.

corners · Postby **corners** » Mon Feb 23, 2009 9:43 pm

Thanks for the info!!

Much appreciated

Fatty · Postby **Fatty** » Mon Feb 23, 2009 9:49 pm

i would have thought a simple fuel piggyback (of course, jaycar dfa springs to mind) could possibly solve the issue above 5000rpm. it could be worth further investigation, as it'd be a lot cheaper than going to a full standalone ecu. altho of course it won't give you as much tunability.

Postby **Okibi** » Mon Feb 23, 2009 10:26 pm

Les, i thought other club members also went the wolf as part of their shortnose to 1.8 upgrade? Rod? Neville?

ampz · Postby **ampz** » Tue Feb 24, 2009 9:26 am

The CAS (crank angle sensor) is different between the 1.6 and 1.8 ecus.
The signal starts to differ @ higher rpm's, on the na6 the signal gets way noisy up there (shifts phase is the best way to describe it) and the ecu reads the sync differently.
I am pretty sure the 1.8 cas is different internally (hall effect and not optical) which sends a slightly different signal, which confuses the ecu.

corners · Postby **corners** » Tue Feb 24, 2009 7:11 pm

I was speaking to a guy today in QLD who used to race and work on them and he advised against the 1.8 upgrade as the coil is different which causes problems.

This is a hard decision to make as there are so many mixed reports....