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SR20 CAS or timing

Practical Engine Building

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I have trouble starting my car after replacing my head gasket. I've sent my timing perfect after watching and reading heaps of forums of how to time it

but it still doesn't start ... it turns over or cranks but then a big bang happens out the exhaust then stops


Any chance you have the cams 360 deg out (ie, half-turn on cams, or distributor), and need to change an offset in the ECU?

Here’s my cams

cylinder 1 intake and exhaust cam lobes are facing outwards and intake dot mark is about 10 o’clock and exhaust pin is 12 o’clock

11 links from dot to dot

and the crank timing marks is on TDC (second notch from the left(as your looking down at the crank))

i aline the CAS perfect (alining the notch on the CAS with the right dot and as you push it in it flicks to the left dot on the CAS) and having the bolt holes for the CAS perfectly in the middle

what am I doing wrong

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Your process and the picture attached looks fine to me.

Are you still using the stock ECU? Because if you are using a standalone and the tuner didn’t adjust the base timing properly it could be anywhere. Only way to know if it’s correct is to put a timing light and check it.

i have linkG3 ecu

is there away knowing how to check base timing on the laptop??

i cant seem to start it to use the timing light? or can i ?


Pull the spark plugs and turn it over on the starter, if you don't get the timing light lighting up it indicates a timing issue.

What David means is it is possible to have the distributor, if used, 180 degrees out, which is one crankshaft rotation. What this means is that instead of firing just before TDC on the compression stroke it may be firing just before TDC on the exhaust stroke, and it's possible the spark plug is igniting the unused fuel-air mixture in the cylinder while the exhaust valve is open, and this is igniting the fuel-air mix in the exhaust system. I know from experience this can be a VERY loud bang and, in some circumstances, it can actually blow the muffler/silencer out. Examples here - https://www.google.com/search?source=univ&tbm=isch&q=exploded+muffler+image&client=firefox-b-d&fir=8xviY9X42TEcsM%252CtnUJegWOkK8rLM%252C_%253BbZGGpVOCMI-JOM%252CrSd-5XJnGBi4vM%252C_%253ByNDG3blcIJKWwM%252CUP0dFLskF0PgjM%252C_%253BIQslu39S9taMNM%252CStkvWGKOCBcOGM%252C_%253BDmDnjeHQ3JfVqM%252C_kejHb6JQROjwM%252C_%253B0Q7Gj-t3dt6LKM%252C685RjGR8vp1hoM%252C_%253BZeibwZqY0p63LM%252CyLX1fi-xXeNOmM%252C_%253BAlgBr88n9xY6xM%252C8USylRrsvhjmJM%252C_%253BMn-upi8ZTz79_M%252C8USylRrsvhjmJM%252C_%253BNQrHUbxTGjJVOM%252C9pMFgjK-aGKozM%252C_&usg=AI4_-kRMcr5z4Bz-26NHE9zXgcHNOmfCmg&sa=X&ved=2ahUKEwiA1Yj45_v7AhW_mlYBHVdmBDoQ7Al6BAgKEEs&biw=2144&bih=1138&dpr=0.9

ok ive tried to reset the timing to the compression stroke

so just to clarify ,to set the timing to the compression stroke ,I have to turn the engine with spark plug 2 3 4 out and leave cylinder 1 spark plug in and keep turning until it gets hard to turn on TDC?


That's possibly the easiest way, the compression stoke will be very obvious.

If it has a distributor, check the rotor is pointing to the spark plug leading to that cylinder. If it's what I suspect, it will be pointing at the opposite cylinder. If so, you have two options, remove the distributor and turn the rotor 180 degrees and refit, or what I would do is swap the 1&4 and 2&3 lead positions in the dissy cap.

If that isn't the problem, at least you've eliminated one thing.

If it doesn't have a dissy, but a cam or dissy sender for which part of the cycle the engine is on, check to see what the offset is and add, or subtract, 360 degrees and try that. If it is the latter, you could pull it and rotate it by 180 degrees for the same effect.

the sr20 engines dont have a distributor in the nissan silvia S15 (to my knowledge) ,they have coils and Crank Angle Sensor (CAS)

im still kinda lost in what to do now

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