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german240

L28 Stroker Build - I need your advice :-)

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3 hours ago, madkaw said:

Don’t think of it as “too soon” , but advanced 3 degrees Cliff. It’s already ADVANCED , so moving sprocket would advance it more . 

Here's where I'm confused. 

The motor turns clockwise, 11 comes before 8 going clockwise towards TDC.  Does that not mean 11 would open sooner?

TDC2.png

 

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Actually it is "too" soon if you're comparing to the cam card.  I just look at the B or the A in BTDC (before top dead center) and ABDC (after bottom dead center), and the like.  If the B number is bigger than the cam card, then it's sooner, more advanced, more early, more "before".  But if the A number is bigger then it's later, more after.  The numbers are in relation to the "dead center" point chosen. You can recalculate them in other terms if you want.

The ATDC number is the one that's not early.  It's a bigger "after" number.  I missed it.  Two bigger B's, one smaller A, and the bigger A (the later than the card timing event).  Edited (again) - don't know my A's from a hole in the ground.  Original version in madkaw's quote.

Delta cam must have large tolerances in their specs, or sloppy equipment.  Most people wouldn't check the quality of the job like german240 did.  Disappointing that they couldn't give a good answer to the question.

image.png

Edited by Zed Head
typo dang it

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3 hours ago, siteunseen said:

Here's where I'm confused. 

The motor turns clockwise, 11 comes before 8 going clockwise towards TDC.  Does that not mean 11 would open sooner?

TDC2.png

 

Simple answer is yes 

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4 hours ago, Zed Head said:

Actually it is "too" soon if you're comparing to the cam card.  I just look at the B or the A in BTDC (before top dead center) and ABDC (after bottom dead center), and the like.  If the B number is bigger than the cam card, then it's sooner, more advanced, more early, more "before".  But if the A number is bigger then it's later, more after.  The numbers are in relation to the "dead center" point chosen. You can recalculate them in other terms if you want.

The ATDC number is the one that's not early.  It's a bigger "after" number.  I missed it.  Two bigger B's, one bigger A, and the smaller A (the later timing event).

Delta cam must have large tolerances in their specs, or sloppy equipment.  Most people wouldn't check the quality of the job like german240 did.  Disappointing that they couldn't give a good answer to the question.

image.png

ISKY sent me the wrong card with my cam. I spent a day turning my engine over and over and rechecking numbers to try and make them come out. I finally got him on the phone and we cleared it up. It’s frustrating if you don’t do this a lot or are not confident of your skills- you swear your doing something wrong when your not. Not easy telling Mr. Iskerdian his cam card doesn’t make sense . 

I also never hit my numbers exact. Lots of slop in rocker arm ratios and other variables. If the cam grinder says they are good numbers then go with it

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Fixed my error in #102 about the smaller "A" being the "later" event.  Confused myself this morning.  

german240 ended up with more duration on both valves so might be better off in the long run.

 

 

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I left it like it is. Double checked valve-piston clearance (it is >2mm) and piston-head clearance (1.5mm) using a strip of solder. The engine is complete so far, I just have to fit the Zstory race manifold and the fully refurbished SUs. 

BTW: Some cam grinders like ISKY supply two completely different cam cards. One as reference (advertised), one for actual numbers that can be measured with a degree wheel. I found a similar (advertised) spec cam card, the "workshop specs" come out like my measurements did. 

@siteunseen I just realized that you uploaded those cam cards. :D 

 

Better pictures will be added next week :) Just some quick shots. 

 

2017-12-04 20.37.49.jpg

 

2017-12-04 20.37.41.jpg

2017-12-04 21.03.48.jpg

DIstributor shaft alignment..shifted it around many times, hopefully it is right now :D

2017-12-03 16.39.00.jpg

Header

01300638.JPG

 

 

Aaaaand.... Engine before I started working on it :D

P1130774.JPG

This was the Ebay ad..

l28 2.JPG

Edited by german240
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That's a good looking motor! I don't know why but a sexy motor stirs something deep down in side me...:blush:

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Bad news. I talked to an experienced engine builder. I told him that I only measured 1 piston ring gap (I seriously don't understand why I did this). He strongly recommended to start over, and that's what I am going to do :(

..first engine, lesson learnt! I just hope that I won't run into any issues with reusing the head and rod bolts. 

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Awe man, bummer.  When I tore my head gasket and had to pull the head off my newly rebuilt motor the forum said that since the head bolts hadn't been through a heat cycle they should be fine to re-use.  That was two years ago and no issues since.

 

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A friend of mine just checked his piston ring gaps. He got exactly the same  rings+pistons, same bore (same engine shop), all gaps were within spec (on the tight side, though). It is very unlikely that my gaps would be any different... However, I might still tear it all down again. Let's see. 

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1 hour ago, german240 said:

A friend of mine just checked his piston ring gaps. He got exactly the same  rings+pistons, same bore (same engine shop), all gaps were within spec (on the tight side, though). It is very unlikely that my gaps would be any different... However, I might still tear it all down again. Let's see. 

In theory they will all be the same but sometimes cylinders vary a little bit after honing. It's cheap insurance while the motor is out to go ahead and check them all. Do you have a bore gauge to check run out?

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I wouldn't say it's cheap.. All new gaskets, new bolts and a lot of time. My friend  had exactly the same ring gaps all around, no variance at all. But you still are right! 

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Unfortunately you can’t take that for granted that all the rings are the same. 

Why and what new bolts are needed?

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I would reuse everything gaskets, bolts, etc. The time is cheap compared to destroying a freshly rebuilt engine

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The question is: What are correct ring gap specs for this application? It is not a KA24E engine (where the pistons are from), nor a stock L28.

NPR (Japan ring manufacturer) lists the following ring gaps:

gap.jpg

I'm still undecided :huh:

@madkaw are you sure that the head bolts (got new OEM turbo bolts) are not a yield type?

Edited by german240

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7 hours ago, german240 said:

The question is: What are correct ring gap specs for this application? It is not a KA24E engine (where the pistons are from), nor a stock L28.

NPR (Japan ring manufacturer) lists the following ring gaps:

gap.jpg

I'm still undecided :huh:

@madkaw are you sure that the head bolts (got new OEM turbo bolts) are not a yield type?

you'd gap the rings for the pistons, so surely you'd gap as per ka24e engine specs/manual?

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I would think you would gap per the ring manufacturer specs like the ones you listed based on the piston they're on. I would think ring position relative to combustion and the size of the groove in the piston is the overriding factor not the block they are mounted in. I would think a flame front is a flame front. I suspect compression has more effect on the rings than what the engine is...

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Piston and piston ring gap are totally independent. It all depends on ring material and block material as only the difference in thermal expansion is relevant. That's why I won't find a perfect answer, realised this today :)

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Those are wide spec ranges.  Builders tend to open the gap if they expect a hot running engine.  Even if you had stock pistons you'd probably still not have a clear answer.  Those KA pistons aren't that much different from stock, and you don't have a turbo or anything special.  Just avoid the small number and you'll probably be fine.

Another interesting topic that we can spend lots of time on though.  Thanks.

http://www.acl.co.nz/wp-content/uploads/4-Compression-Ring-Gaps-For-High-Performance-Engines.pdf

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So I decided to not tear the engine down again.

NPR states in the piston ring manual:

Quote
NPR manufacturers each piston ring gap with the correct OEM specification for each individual engine. There is no need, nor do we recommend that you alter them in anyway as this might void our warranty. Also note these end gaps are set at
exact bore dimensions.

20171211_172615.jpg

20171211_172603.jpg

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Update! The engine is running ?  Got A/F ratio dialed in pretty well (using a wideband probe). Timing set to 16° BTDC initial, around 35° maximum mechanical advance. 

Only issues I'm still fighting with: When shutting down the engine, it rattles/shakes a little. Is this something unusual? I don't have another Datsun engine to compare, so I don't know if it is supposed to be like this. 

Besides that, the front nozzle of the SU carb sticks sometimes after the choke has been applied. Cables are greased, so are all pivot points. Should I try to bend something? 

 

Edited by german240

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 I twisted the little flat bar linkage piece that pulls the nozzle down to ensure the linkage mating surfaces were exactly parallel to the attachment points. That allowed the nozzle to return from the choke position easily. Carb. was removed at the time. I doubt that it can be done with the carb installed.

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That is an odd sound on shut down.  I wonder if it could be as simple as the noise heard through the carbs with no air filter installed?  Sort of sounds like something is loose?  Is the valve cover nice and snug?

Edited by siteunseen

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So far I haven't found something loose. It's not only a noise but also a visible shaking - maybe a form of dieseling? 

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