L20b A87 rebuild help, please.

[sil8y]

I bought another 71 wagon a few months back. Has an L20b with a closed A87 head. Started loosing power. So, I ran a compression test and found all at 90-92psi. Pulled head and had a very light head gasket failure between 2 and 3. Brand new head. Checked valve adjustments and its OK. Checked all surfaces with my bluepoint straight edge and could not even get .002 feeler through anywhere. Well within spec. New timing components and a L20 cam. However, the bottom end looks original and is showing signs of a little trust wear in the bores. Poured a little diesel in the cylinders and none leaked past the rings after sitting for a few hours. So, I thought it OK. Reassembled and set timing. I believe the previous was a tooth off. Ran another compression test and only got 100psi but ran much better.
Now I'm loosing power again and want to rebuild the bottom as I'm pretty sure the only weak spot left it the rings. But, I want to bore out and change pistons. I understand I can use some flat top 280 pistons and increase compression to 11.1-1. My question is, will this change the deck height and require rods as well. Also, do I need a different head gasket for the bore? Should I get different head bolts to hold the higher compression? Any help, insight, advise or warnings is appreciated. ...also, I'm trying to get this done this week. So, I need to get parts here very soon.

[okayfine]

11:1 compression is A LOT for an L-series. That's not going to be a pump-gas motor. Have you planned out everything else to support that compression?

Your questions will be answered with "it depends" without you naming your specific piston. Are you sure you can even source four pistons of your desired type? They're not all that common any more. Without more details, you'll be fighting detonation, not headgasket issues. ARP head bolts are better, not sure they're really required here compared to the Turbo Nissan bolts.

[bertvorgon]

I have 10:1 in my motor, and it will not run on Chevron 94 Octane at all. Anymore than the slightest attempt at opening the throttle and it will ping then detonate.

[funwithmonkeys]

I am running 10.5:1 and that was set up for 94 octane. I run a bit of octane booster just to be sure I don't have a problem if I get a tank that is not the rated octane level. I was told by Andy that it is just about the limit of what you can run on pump gas.

[sil8y]

OK. Well I guess i heard wrong. What is THE piston rod combo for the l20b/a87 combo. I would like to go a little bigger than stock as I don't want just oversized rings on a honed block with a stock piston. Deck if flat has no
It been recut down. Advice? Previous experience? Head gasket recommendations?

[sil8y]

...deck is flat and has not been recut down.

[sil8y]

As I understand it, l20 dish pistons with a87 head is at only 9.1-1. I was looking for a bigger bore and higher comp set up. Am I not correct on the compression numbers?

[510rob]

If 11.1:1 is good, then why limit yourself there; why not build your motor with >13:1 compression?

Seeing as how you will need to feed it fancy gas for the planned 11.1:1, then you might as well maximize the good of that $20/gallon gas and run as astronomically high of a compression/expansion ratio as possible and really shoot for the moon!

[sil8y]

...umm, no. I'm looking for a better performing daily. I've had a few car with 11-1 on 93 octane clear fuel that get local with no issues. ...however, not an L series. That's why I'm here asking for help. How about a more realistic idea please.

[okayfine]

How about a more realistic idea please.

Your L-series recipe book:

viewtopic.php?p=25814#p25814

[okayfine]

Further, an L-series is 50+ year old engineering, and much has been learned in the decades since. Modern cars run 10:1+ on 87 octane, but that's with all those engineering advances, and so does not apply.

Your goal is a "better performing daily" and IMO a stock rebuild, 9:1 compression, mild cam, set of SUs, a nice exhaust system, and EI will give you that. More wild and you start sacrificing driveability, or spending ages on the dyno tuning a pair of DOCEs. Power's made in the head, and there's much you can do on a stock head to improve flow.

The long-rod 2.1 discussed in the link above would make an awesome motor and streetable too, but finding the parts required might take some time and so it's going to be done in a week.

Other links of note:
The 510 Archives https://drive.google.com/folderview?id= ... E0MGY3NTA1

Check out the How to Modify book (the original Bible), the How to Hot Rod book (Bible reissue with L20B info), and here:
https://drive.google.com/folderview?id= ... E0MGY3NTA1

for DQ Volume 12 Issue 3 - Tech How-To: Cylinder Head Modifications - An inside look at cylinder head modifications. Bruce Godfry details some basic steps to allow the home mechanic to achieve 80% of professional flowing results. It is much more than “port and polish.”

[510rob]

...umm, no. I'm looking for a better performing daily. I've had a few car with 11-1 on 93 octane clear fuel that get local with no issues. ...however, not an L series. That's why I'm here asking for help. How about a more realistic idea please.

You know I was joking about my answer, right? (I was...)

+1 on the comment about L-series engines being 50+ year old engineering; the design was initially based on a Mercedes-Benz engine design from the 1950s, so the L-series design is essentially a slightly tweaked 60+ year old design...

Production L-series combustion chambers are pretty much rubbish by modern standards. A good indication as to [how well a combustion space is able to burn the fuel] is provided by [how much advance is needed to get the motor to run well]. If you need to run more ignition advance in design A versus design B, it implies that the fuel is burning more slowly in design A. Burn rate is governed by various mechanical geometry things and related stuffs... If fuel burns more slowly, then it is exposed to high temps and high pressures for longer periods of time, which makes a particular engine+fuel combination more prone to detonation & the resulting problems with pre-ignition...

You need more squish, more turbulence, more swirl, and generally more of the modern magic that's been unleashed by 50+ years of methodically-learned engineering.

Or, just take the L-series for what it is --> a 50+ year old design that works adequately for most purposes and which has a handful of quirks and limitations.

But an L-series is faithful like an old dog. It isn't the fastest runner, but it is pretty loyal if you are nice to it

[bertvorgon]

I like my old reliable dog, he greets me with a nice friendly growl, then purrs like an old cat, when out cruising the streets, then, when we head out onto the highway, that old mean streak comes out occasionally, snapping at the odd high strung, young bitch, sending them off with their tail between their legs.

Loyal is good in the long run.

50+ years, eh, I had not thought of it in those terms..YIKES!

[Byron510]

Yep - well my completely original 1968 L13 car, which hasn't even had its head gasket changed yet, is still running around. Reliable, yes. Fast - certainly NOT!

Ole Blue just chuckles at Mr Vorgons ride, and at the Bronze which is quite a bit louder and generally close by I might add. Kind of like an old man on a scooter driving down a country lane.

But Rob and Julian are right - don’t expect miracles out of the ‘L’ motor. But damn they are tough as nails, take a shit kicking and are about as simple as it gets to build - god willing we continue to be lucky enough to still buy parts off the shelf. You know, the old ‘L’ motor does my cars proud, and makes the 510 what it is. You know the old adage – if it ain’t broke….

Byron

[James]

While I don't have the breadth of experience that Julian or Byron have, I can give you my experience.

I took an L-16, added L-18 crank and rods, closed chambered W53 head, mild cam and SU's. I have driven this engine for 16+ years. Its fun to drive, easy to maintain, keep cool, tune, reliable. I wouldn't trade a few more HP for discounted drivability.