Topic: K7 Piston Kits?

[ckb96124]

Hey Guys,

I'm pretty new on the forum, and have been a lurker for a while.  I've been searching around the forum and I can't really find this topic directly addressed anywhere, so apologies up front if I missed it.

I'm just getting started on tearing down a K7 for a cafe project.  This bike hasn't been on the road in nearly 25 years (17,200 miles on the clock), and though the motor is not seized, the compression at the kick starter seems to be pretty low.  I'm thinking that it was taken off the road for some "catastrophic" problem.  So, I'm anticipating having to bore this thing, in addition to a probable valve job and going through the bottom end.  I haven't torn into it yet - I just want to know what my options are going in.

Anyway, I've been looking around, and I can't really find a first oversize kit for this bike.  CycleX has a first oversize kit that will work, but it has the 69-76 piston (not the more domed 77/78 piston), which will lower the compression ratio on the bike (though the site says not by much).  Z1 has a 2nd oversize kit, and it says something similar ("supersport compression will drop slightly"), but it doesn't address the K7 specifically, so I'm not sure there.  I thought for sure I'd be able to get the kit (at a higher price of course) from Wiseco, but they only have an 836 kit coming up on their website.  I want to keep the motor close to stock for reliability purposes, so I'm going to be running the stock head, valves, springs, etc.

So, my question to you all is, what are you using for piston kits on the K7?  I wanted to go only to the first oversize, but should I just get an 836 kit instead and be done with it?  If anyone has used the Z1 or CycleX kits referenced above, I'd love to hear from you about how you think it performs for you.

Thanks guys - Happy New Year

Brian

[KRONUS0100]

contact ROB at CYCLERECYCLE2 in Indianapolis.  He is very knowledgable about these bikes. I seem to remebr seeing a bore kit for that motor.   But usually, the bottom end will be good, usually its the rings that have tried to sieze in thier grooves.  Let some atf soak for about a week and then redo the compression test.  that few miles isnt really enuff to consider an overbore unless the walls are scuffed.  the cam chain rubbers and primary rubbers are prolly hard, so they prolly need replaced.  not much else can go wrong with these for sitting for so long.

[ckb96124]

It's definitely not seized.  It should have a bit more compression than it does, IMO.  I just don't know what I'm going to find when I open it up.  Thanks for the info.

Brian

[bryanj]

Think if you only want to go 1st oversize you are stuck with Honda parts who dont do a kit you get everthing seperate

[BrianAdair]

my K7 had sit for around 20 years, and it was not seized either, it would turn over but when I tore it down the rings were stuck in the pistons. Mainly the oil ring, would not turn or rotate in the piston.

[ckb96124]

bryanj,

Do you know of a source where I can get first oversize pistons and rings for this motor individually?  That would be great.

Brian

[ZanVooden]

When I tore down my K8, all that needed to be replaced were the rings. The pistons were fine. I was actually able to even stick with the standard sized rings. Before you go looking for pistons, I would tear it down and check if you actually need pistons or just rings.

[ckb96124]

Agreed.  I was just trying to understand the options that are out there.

Brian

[BrianAdair]

K7 rings are not real easy to find, unless you get OEM, and they are around $45 per piston.
I tried K0-K6 rings and they are just a tad thicker, so if you could have a machine shop open the gap for the rings on your pistons you could use the after market K0-K6 rings.

[bryanj]

Try Motogrid for the numbers then any Honda dealer

[Terry in Australia]

Just get the engine running first mate, before you tear into it. (A lot of restorations stop just after the owner has pulled the engine down and done a pricing exercise on replacement parts, only to discover that the parts cost is three times what you paid for the whole bike)

Drop the old oil and change the filter replacing the oil with good quality motorcycle specific oil. (Carefully) Remove the spark plugs and replace them with new NGK D7EA's, clean your points and re-gap them, check your valve clearances, adjust your cam chain (making sure your adjuster rod isn't siezed) and fit a new battery. Remove your carbs and clean them (properly) with carb cleaner and compressed air, and adjust the float levels.

Fill your tank with fresh fuel, (with a half pint of ATF added for "upper cylinder lubricant) pull the choke on, and fire it up. Once it's running and warm, get your timing light out and adjust your ignition timing. (on both 1&4 and 2&3) Take it for a good long ride (not just around the block, minimum 20 miles) and on return, while the engine is still warm get out your compression gauges and check the compression, it should read around 150 - 170 PSI per cylinder.

Anything less than 120 and it's time to think about new rings, (or you could have a buggered exhaust valve) but as has been said above, it probably won't need new pistons, unless some "half arsed home mechanic" has been stuffing around with it previously. Cheers, Terry.