I finished my engine rebuild, installed and ran the initial 20 mins new-cam run in procedure, everything looking good.
Changed oil and filter and went for first run, had some issues with pinking to start off with but after retarding the ignition slightly its ok.

Problem is when i switch off the engine it keeps running for about 10 seconds, shuddering violently....

Engine is now at 10.9:1 CR, i checked the plugs and they look ok. i'm using the same plugs as before the engine mods... would a change to a cooler plug help?

I checked that the Anti diesel valve on the carb is working, I'm still using the std Hitachi carb for the time being. Using 95 octane benzine. Ignition is at around 5 deg static, both vaccuum and mech advance are working ok.

any suggestions on best thing to look at to cure this ?

OK, good news, thanks....

i put my engine together only to read the wiki about the rod bolts which says they should be renewed every time...
Luckily engine not yet back in the car, but its a pain to take out the old ones and put in new ones...
The ones i re-used didnt seem distorted at all, and when i rebuilt my standard A14 3 years ago i just re used them (different ones by the way)and had no trouble....

The ones i have just re-used came off an A15 and this is the first time they've been removed...

is it too much risk to re-use them ?

Sounds like you need a 60A type, that is the 5 speed with the normal shift pattern, it also has a slightly higher 5th gear.

are those bigger valves than normal ? look different to mine, and mine have the nissan logo on them...

OK, even though I eventually went for Mazda UC pistons at 77mm i thought i would post up my machine shop costs..
Had them translated today as i cant read Thai..

polish crank - 300 baht
bore 4 cyl bores to 77mm - 800 baht
open out small ends to fit Mazda pin - 600 baht
machine 1mm from top face of pistons - 400 baht
assembly of 4 pistons with rods and pins - 600 baht

total 2700 baht = approx 75 USD or 104 AUD

Pistons and rings were about the same price over again

OK, i'm an idiot... repeat after me.. "it is only by doing that you learn"..


Following Neils Post i decided to take a step back and recheck everything i have done... well, due to me being 'sure it was like this' when i built the std engine 3 years ago i had the cam about 180 degs out with the crank.
Now I aligned it properly as to the picture in the Wiki i get 3.5 and 3.3mm clearance .
So ive continued with the pistons just as flat tops.

With 30cc in the head, 1.2mm HG (6cc) and the step on one side of the mazda piston (est 1cc) i get a CR of 10.3... Camtech recommended a minimum CR of 9.. i run 95 octane petrol, so i think all should be good.

Yes, i'm still using the thin steel washers that sit at the bottom if the springs, i assume those are just for wear purposes..

Hi Neil,
According to your cam spec you have .309 lift at the lobe, with 1.65 rockers that gives .309 x 1.65 = .509" lift = 12.95mm

My cam spec(camtech 621) has .399 valve lift with 1.5 ratio rockers, this calculates back to .266 lobe lift. I'm using the std rockers at 1.44 ratio, so my lift should be .266 x 1.44 = .383" = 9.72mm..
So you have about 3mm more lift than me.. i would be hitting the pistons for sure... yet you have no problems...?i must have someting different somewhere, maybe its to do with the cam timing ?

I wonder if my head has been skimmed in the past... I cc'd the chambers and got about 30ml which according to tech wiki is correct...so i asssumed not.

ok next question, i think i know the answer but just to check what you guys think....

See the picture, the Mazda piston has a cut out one one side, i assume this is for valve relief with the std mazda head.
if you install the pistons with the 'F' to the front (as i have done so far) then the cut out is on the side of the engine with the spark plugs, and with the H89 head where the Quench is.

Would it be better to install the pistons backwards? so the quench portion of the head is presented with a flat part of the piston and the cut out goes on the other side ?

That is my thinking.. the 'F' is just an aid to people rebuilding a std engine...

pretty important to decide before i start to cut the valve reliefs.....

EDIT... my bad, im getting confused with seeing the head upside down.. pistons should be fitted with the F to front as this aligns the flat part with the squish correctly.

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  mazda UC piston cutout.jpg (98.90 KB)