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1986 Honda Nighthawk 700S pistons

This is a discussion on 1986 Honda Nighthawk 700S pistons within the Motorcycle Repair forums, part of the General category; I just bought an 86 Nighthawk 700S. Two good friends of mine (one a master mechanic, the other his apprentace) ...


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Old 04-08-2006   #1
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Default 1986 Honda Nighthawk 700S pistons

I just bought an 86 Nighthawk 700S. Two good friends of mine (one a master mechanic, the other his apprentace) and I have been working on it for a few days. The main problem we ran into was a lack of power and backfiring. So we pulled and cleaned the carbs, changed the oil and plugs, etc.

Yesterday, we did a "dirty" compression check (no metric fitting for gauge), and number 3 was weak. So we put it back together and it runs great ... as long as the ignition wire for number 3 isn't plugged in. We're assuming the rings are leaking, so we want to replace all 4 pistons and rings.

The problem is when I look for replacement pistons, I can only find oversize, the smallest 0.25 over. Does anyone know where I can get the standard size pistons? If I have to put oversize pistons in, my questions are: 1: Do I have to have the head bored out to match the pistons, and 2: Do I have to do anything to the carbs (ie new jets) to compensate for the larger cylinders?

Thanks in advance.
Lorrene B is offline   Reply With Quote
Old 04-09-2006   #2
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Default 1986 Honda Nighthawk 700S pistons

Honda would be the first place I would look for standard sized pistons. The 700 was an odd ball so they might be tough to find as it was only made I think 2 years to beat a 750cc over tarrif stuck on Japanese bikes. You don't bore the head, you bore the cylinders and yes they have to be bored and honed to match the new pistons. You shouldn't need to rejet the carb if you're only going just oversized.

Did you check the valves? If one is leaking or they need adjusted the compression will be low. The backfiring kinda tells me they might be suspect, not the rings.
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Old 04-10-2006   #3
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Default 1986 Honda Nighthawk 700S pistons

Update: Well, my friends decided to tear down the bike. We checked the valves, pistons, and rings. The valves are perfect, the pistons need rings, but are reuseable (clean and not scored), and the walls are good (no scoring, just some blow-by oil). Piston 3 was the worst, 2 and 4 were starting to go as well. I can get the stock rings no problem.

So after we put on the new rings and gaskets and get it all back together the only questionable item is the charging system. The battery keeps dying, but it's suspect.

I apologize if my terminology is off. I haven't been into repairing motors all that long (a little over a year).

I'm a bit wary of owning a bike with this uncommon an engine. From what I'm told though, they will last forever if maintained properly.
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Old 04-10-2006   #4
E R
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Default 1986 Honda Nighthawk 700S pistons

Yeah they are a good engine. If it does go south and ya don't want to fix it there are plenty of crashed 750 Nighthawks around with good engines. Same engine basically I believe.
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