My "L29" build.

jonbills

Membership Secretary
Site Administrator
Maybe it was designed for the flimsier 240z with thinner footwell metal :)
To be honest, It is very big and it is very nicely tucked up into the space. A little bit of fettling was always on the cards.
It'll be worth it in the end.
 

jonbills

Membership Secretary
Site Administrator
Since it's quiet around here, I thought I'd add another interesting factoid from the rebuild.
My rods stretch just about 0.6mm, revving to 7.5k rpm.
I know this because:
1) piston 3 had a carbon free area in a shape that matched the squish area of the head. The other pistons didn't.
5f1df258034d3495079f521713bbe34a.jpg

AND
2) I use a gasket 0.8 mm thick
AND
3) piston 3 was 0.22mm up above deck height and all the others were 0.20mm or less up.

So there we go. And we shaved 0.04mm off piston 3 so that now it's all back together, all the pistons are below 0.20mm up. :thumbs:
 

Moriarty

Well-Known Forum User
24 thou is too tight
Personally I wouldnt go below 35 thou

Rods and pistons stretch, crank and gudgeon pins deflect.....it all adds up
Also to tight a squish can create det
 

jonbills

Membership Secretary
Site Administrator
How do you know it actually touched the head? Would you get a mark if it was just very close?



My interpretation is that on piston 3, there was contact, enough to clear the carbon deposits but no mark was left on the metal of the head or piston.
 

jonbills

Membership Secretary
Site Administrator
24 thou is too tight
Personally I wouldnt go below 35 thou

Rods and pistons stretch, crank and gudgeon pins deflect.....it all adds up
Also to tight a squish can create det


Do you think the stretch/deflection gets worse over time? I was thinking that since I ran it like this last year for a few months with just the near miss on #3 I should be fine now.
The risk of det is one to think about though. Home made arduino knock sensor to the rescue ? :)
 

johnymd

Club Member
How much ignition are you running under load Jon? I'm trying to lean L-series after too long away.
 

jonbills

Membership Secretary
Site Administrator
I'm going to go for about 30 to be conservative initially. For stock heads 34-35 is normally best performance. With a lot of squish less advance may be needed. I aim to find out on the rolling road what's optimal for mine.
 

jonbills

Membership Secretary
Site Administrator
Here's an interesting page I found (linked from wikipedia, so it must be true :))
Suggests best squish has clearance < 0.75mm
I'm pretty sure there was a thread on hybridz.org with a guy claiming he'd built loads of engines with low clearances. (but also many people suggesting about an inch is right on 'Merkan cars)
http://www.billzilla.org/engcombust.htm
 

racer

Club Member
What problems Matt? The same stuff moriarty covered?

Exactly Jon. If you look in the how to book they recommend 50 thou, but modern thinking is absolute minimum 35 thou as Moriarty says.

I'm running 35 thou using a felpro 1mil with no issues. That would still be a bit tight,
so you might consider a standard Nissan gasket.
 

johnymd

Club Member
The other way to look at life is to try and push the boundaries. I've never been one to always err on the safe side or just follow what others have done before. When I listen to my mate who runs dyno cells at ford R&D, they are continually inovateing and thinking out of the box. It's how we evolve and change the way of thinking.
 

Moriarty

Well-Known Forum User
Unfortunately when it comes to piston to head clearance "pushing the boundaries" will always result in serious failure and cost


Sent from my iPhone using Tapatalk
 

jonbills

Membership Secretary
Site Administrator
Here's a couple of the threads I was thinking of on Hybridz.org
http://forums.hybridz.org/topic/58127-best-way-to-achieve-piston-to-head-clearance/page-2
http://forums.hybridz.org/topic/53318-custom-pistons/#entry478561

Given I've already run it for a few months and there was only that slight contact on 3 (now corrected), it seems the only risk down the road comes from bearing wear.

I may live to regret it (and I'll give you all the 'I told you so' moment) but given this, and I expect to be putting new bearings in every few years I'm going to keep it like this.
 

jonbills

Membership Secretary
Site Administrator
Thanks Matt.
I took the manifolds off this evening and gave the footwell a serious beating and I've now got a few mm clearance with the exhaust manifold.

b0804386dc3408557b39ef8b64698821.jpg


So should have the system fitted by in time to go watch the Saints beat Bristol :thumbs:
 
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