fire?

[prilofx]

So, what's this I've read a couple of times about the 240zs with flat-top pistons tending to catch on fire? I'm assuming that's what mine's got in it until I open it up and find out otherwise. What can a person do, besides change these out (if they do indeed tend to catch fire) to minimize the chances of it happening?

Thanks!

[Arne]

April, I've heard lots of different complaints about the US flat tops (which your car does have, I looked at your Gallery pictures), but I can't recall ever hearing about them catching on fire. Here in the US, they are jetted quite lean, and tend to run hot and cause vapor lock, but fire? That's new to me.

[sblake01]

Arne, she said pistons not carbs. Since she mentions opening it up could be she really does mean pistons. Though I've never heard anything about 240Zs with flat top pistons tending to catch on fire........

[Arne]

Saw flat-tops, glossed right over the piston part. April, can you amplify your concerns?

[prilofx]

I may be just confused about terminology. I'll poke around some more and see if I can square it up.

[prilofx]

aha. Got it. I WAS confused. there are flat top pistons AND flat top carbs? Am I languishing in American musclecar-headedness when I hear about differently shaped "tops" and think immediately of pistons instead of carburetors?

[TBone028]

As far as flat-top pistons causing a fire...I would say no, they do not make it more likely to catch fire...unless by fire, you mean detonation/knocking. With flat-top pistons, you would generally have a higher compression ratio then an equal engine with something like dished-pistons. A simple example would be flat-top pistons have a 9:1 compression ratio, dished have 8:1.

If you were to have a high-compression engine with flat-top pistons, and were to have a lean condition or low octane that caused knocking, then yes, it could eventually lead to damage to your engine. Simple fix? Run higher octane like premium gas. If that still doesnt work, then you could retard your timing.

Flat-top carbs or Round-top carbs seem to be a term that is specific to SU carbs and Datsuns. They refer to the edge of the piston chamber of the carbs. The more gentle, rounded curve are the Round-top SU carbs found on 70-72 240Zs. Flat-tops are from 73, and some 74 260Z's.

Detailed info here: http://www.zparts.com/zptech/tech_tips/izccposts/su_differences.htm

Sorry if this was an overly basic post, it seemed like you had some confusion.

[prilofx]

I did, T-bone! Thanks! Haven't spent any time prior to now working with these cars- it's been EFI Toyotas since '95. So, it's a new vocabulary in some areas.

[Bruce Palmer]

So just around the corner the second weekend in JUNE is DATSUN DRIVING CANBY FUN at the Clackamas County Fairgrounds in Canby just outside of Portland. Would love to see you show up. We at Ztherapy are planning on being there and if all works out, will have an early carb "Show and Install" for all to take in.

For info on Canby go to www.datsunsnw.org

In the mean time we sell a DVD on the early SUs (Hitachi variants) that you might want to consider replacing your flat tops with. A $25 teaching tool worth every penny from what we hear back from customers.

[prilofx]

Totally hoping to get the car roadworthy for summer, Bruce! But even if it isn't, if that's during the transition from spring term to summer term, I'd definitely like to come up to check it all out in our Bomba Azul (the 4runner).

[Arne]

Canby is a good place to meet most of the Oregon CZCC group. Here's some pictures of the group caravan going in last year.

[Mike B]

Canby is a good place to meet most of the Oregon CZCC group. Here's some pictures of the group caravan going in last year.

Don't forget the Washington CZCC folks who make the drive down too. At least two of them are in your photos .

-Mike