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post #1 of (permalink) Old 01-11-2000, 10:12 PM
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Knock

Since the rebuild on the 1.3 it's been running great. But everytime I run up a hill or step hard on the accelerator I get a slight knock. I checked the timing, valve adjustment, and I have good gas in the tank. The only thing I can figure it can be is the stock carb on it. Any thoughts?!?!?

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post #2 of (permalink) Old 01-11-2000, 10:36 PM
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Re: Knock

im not really sure but i think that it might just be because its a 4 cyl. my nissan does the same thing.




86 zuki almost ready to come out of garage

post #3 of (permalink) Old 01-11-2000, 11:15 PM
 
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Re: Knock

If it sounds like the knocking when you have poor octane gas i'd try some super unld and see if that helps.
What about your spark plug gap is it correct? If the super helps the pinging any i'd try advancing the timing a bit . good luck

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post #4 of (permalink) Old 01-11-2000, 11:19 PM
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Re: Knock

The spark gap is .031. Timing @ 10 degrees. I filled the tank with super. I'm starting to think its the carb. I still have the original in it. The knock only happens when going up hill, or I punch it.

post #5 of (permalink) Old 01-12-2000, 04:11 AM
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Re: Knock

Here's a thought....when you completed your engine rebuild, you put in new spark plugs, right? If so, were they the correct heat range for the engine?
Here's another thought too... when I completed my 1.3 rebuild recently, I checked the vacuum pot for the distributor advance and found that a tiny leak in it would not allow the vacuum advance to respond as fully as it was supposed to.. This might not lead to the detonation that you're concerned about but it's worth checking out as you could end up with burned valves and cat. if your engine is running too far retarded because your total ignition advance is missing some of the vacuum advance due to a small leak in the vacuum pot's diaphragm. Check the flyweights in the distributor too for free opening and return. Setting the timing @ 850 rpm doesn't mean much if your distributor won't give you the right advance curve up the rpm range.
Have you eliminated the possibility of air leaks at the carb base and the throttle shaft bushings too?

post #6 of (permalink) Old 01-12-2000, 07:24 PM
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Re: Knock

Checked for vaccuum leaks ect...no joy their, they looked good. I have the timing set at 10 deg BTDC. Is that right or should I retard it some?

post #7 of (permalink) Old 01-12-2000, 09:26 PM
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Re: Knock

what does the sticker under the hood call for for ignition timing? something tells me they are asking for 8 degrees, but my memory could be off. i would try getting the tank down to empty, and then filling up with some of that really high octane stuff out there, like 94 or higher, just as a test. then you'll know for sure it's a timing thing. you could sure try setting to 8 degrees too, at least as an experiment. my 89 sidekick wants 92 octane all the time. i get a bit of ping off the line if i use regular, because i hook up the clutch just off idle. i would get ping at higher demands for power too, so i use the better stuff, and advanced as far as i could go to take advantage of the 92, which wasn't much. just some thoughts rolling around in my head......

post #8 of (permalink) Old 01-14-2000, 01:29 PM
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Re: Knock

This is an interesting situation to me, I've battled with ignition knock many times over the years with Brit sports cars etc and have never really been sure that I've
cured the problem with the right approach-the ideal is to run the engine on the lowest (cheapest) octane possible, right?
The "octane" of gasoline can be viewed as a measure of the relative speed of combustion of that fuel with another gasoline of a different octane level, the higher the octane #, the slower the burning process or flame-front during combustion of the fuel in the cylinder.
Too fast of a flame-front (lower octane fuel) can result in a secondary flame-front developing and the result is more than one combustion event in the firing cylinder and therefore the characteristic knock or pinging noise of the uncontrolled, secondary combustion process in the same cylinder.
Some of the contributing factors that I've learned of to this secondary combustion in carb. engines can be any one or more of the following conditions: quality and octane consitency of the fuel used, incorrect initial timing setting, incorrect operation of either the vacuum and mechanical advance of the distributor ,altitude (timing should be referenced to the altitude range in which the engine is operated), incorrect type of spark plug i.e. heat range and exposure of the central electrode of the plug, exhaust valves not sufficiently seating and therefore cooling correctly thus causing pre-ignition from overheated valve "land " areas (check them to the specs shown in the shop manual), the actual compression ratio of the engine, temperature of the engine's induction air at the carb.
-Have you had the total ignition advance of your distributor scoped at all ?
-What's the characteristics of your engine? i.e.- 1.3 lt with what stage pistons, stock or high compression?
- What readings are you getting for warm cylinder pressures with a compression gauge (throttle fully open)?
-Did you have proper a valve grind when you rebuilt the head ?
-Have you tried different heat ranges for the plugs if your running higher than stock compression?
-Do you have the correct thermostat in the cooling system- this will determine the correct operating temperature of your induction manifold..

Keep us posted, I'm curious to know if you've founs a solution yet.
Best o' luck

post #9 of (permalink) Old 01-14-2000, 08:21 PM
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Re: Knock

AJM, You made some very good points and have some interesting questions. I'll try to answer some of them:

Have I had the total ignition advance of the distributor scoped? No, but from what I can tell it is working properly. I just might take it in to get check though.

Engine charactistics. 1987 Sam 1.3 with standard pistons and rings. totally stock everything.

As far as the head, I sure hope the shop grind the valves properly. I have good cylinder compression on all cylinders 190 /- 5 psi.

I haven't tried different heat ranges with the spark plugs yet. I will this weekend (payday)

The question about the thermostat has me thinking. Prior to the rebuild I didn't have a thermostat in it. I had no knocking what so ever. After the rebuild I installed a 195 deg thermostat. It was the only temp rang I could find for it. Could this have something to do with the knocking? Very interesting! Are their 180 deg thermostats availible for these engines?

Thanks for bringing up your questions and maybe some answers. I really appreciate your help! I'll keep you posted. Aloha!

post #10 of (permalink) Old 01-14-2000, 09:06 PM
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Re: Knock

No thermostat? This was bad,bad, bad!! Without a thermostat, the coolant water will take the path of least resistance around the water passages i.e. the shortest route.
A possible scenario here is steam pockets developing in the cylinder head or block at the furthest location from the water pump. A steam pocket will further prevent water flow.
Check the Sami cylinder head gasket, you'll see that the small holes in the gasket are intended to promote some back-pressure in the water flow so that the water flowing through the cooling passages will pentrate to all the cooling surfaces of the block and head. No thermostat means reduced back pressure for the total cooling system.
Possible results of running for an extended period with no thermostat: blown head gasket, warped head, cracked block, burned valves, scuffed pistons, take your pick...
My Sami engine had a warped head and blown gasket when I bought it- 2 reasons for that I think, the old thermostat was not opening fully and the secondary seal on the rad cap had a small crack in it. Result of that was, loss of full pressure in the cooling system and no vacuum recovery of coolant from the expansion tank when the engine was shut down.
I'm now running with a 195 deg thermostat and a new vacuum pot for the distributor, no knock so far.....

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