880 parts

I am doing a little rework on a friends bike. we are taking these out.



and replacing them with these. yup the JS light weight stuff. we had to work with jim as I think this is the first 880 set he has done. so far I am very pleased with the quality of this stuff. to bad it is hidden.



did a rebalance to the assembly because of the MASSIVE difference in the reciprocating weight. the motor is an 880 with head work, megacycle 5600 cam and the FCR 35 carb's. still have a ways to go as the rings have to be file fitted before I can fit the cylinder to name a few. once it is together it will need some time to get the carbs jetted. fun times though. :mrgreen:

A Windy Thread!

I'm all in. :wink:

good choice on the cam

when I rebuilt my motor two years ago I also opted for the Megacycle 5600

it is a truly excellent all around street cam without radical lift

I sent my lifters to Megacycle and they matched them to the cam they sold me, great people

Oh, so you got the other pair. Jim

yep that's me :mrgreen: it is amazing how much lighter this stuff is compared to the venolia slugs.

comnoz said:

Oh, so you got the other pair. Jim

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Yeah, they don't get much heavier than them old Venolias- or much tougher. Jim

it is a nice street cam if you have the increase in compression to go with it. I would not recommend it with a stock low compression 850. another one I like the numbers on is the web cam 12A but I have not tried one yet. I am DONE with cams from England as I have seen to much inconsistencies.

1up3down said:

good choice on the cam

when I rebuilt my motor two years ago I also opted for the Megacycle 5600

it is a truly excellent all around street cam without radical lift

I sent my lifters to Megacycle and they matched them to the cam they sold me, great people

Click to expand...

it also is a testament as to how tough the con rods are to put up with that much piston weight.

comnoz said:

Yeah, they don't get much heavier than them old Venolias- or much tougher. Jim

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still in the fitting stage of this. as always with hot rod parts you some times have to massage them to fit. in this case it took a little time on the lathe. I had to cut a .060 x 180 squish ring so the pistons cleared the head. it can make a man nerves with pistons that cost what these do.

bill said:

still in the fitting stage of this. as always with hot rod parts you some times have to massage them to fit. in this case it took a little time on the lathe. I had to cut a .060 x 180 squish ring so the pistons cleared the head. it can make a man nerves with pistons that cost what these do.

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You must have a milled head. Be sure to check valve to piston clearance.

bill said:

it can make a man nerves with pistons that cost what these do.

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Me = :shock:

Windy: Tom's 880 is in good hands.

head does not appear to be milled as the step measures .120. the pistons are .100 proud with no base gasket. was JUST touching with the .060 head gasket. it looks like the pistons were touching at the exh port side of the head.

jseng1 said:

You must have a milled head. Be sure to check valve to piston clearance.

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You are essentially installing a big bore kit. 79mm Hi C.R. pistons need a larger diameter combustion chamber (squish band) to fit the larger diameter pistons. Any Hi C.R. piston over 78.5mm requires this (920cc kits with Hi C.R. etc). Instead of enlarging the combustion chamber - you have chosen to cut the pistons to fit the head and that is just fine. But most people cut a larger diameter squish band into the combustion chamber which is more difficult. JS Medium C.R. 920cc pistons do not require larger diameter combustion chambers because the pistons stay below the mating surface of the head.

The head gasket I sent has a bore greater than 79mm so that will be fine. The periphery of your piston tops were probably hitting the smaller diameter mating surface of the head and not the head gasket.

Your pistons protrude .1" above the cylinders. When you put on the head gasket that piston protrusion is reduced to .060" with a .040" thick Head gasket (in your case its reduced to .040" protrusion with your .060" thick head gasket). So with the stock depth of .120" for the step in the combustion chamber you will have .060" vertical squish band clearance with a .040" thick head gasket and .080" vertical squish band clearance with your .060" thick head gasket. This is plenty of clearance - .040" squish band clearance is the absolute minimum. I do not recommend less than .045" vertical squish band clearance to be safe.

Cutting your piston periphery down by .060" as you have already done should give you .040" vertical piston to head clearance with your .060" thick head gasket. So you are good to go (but double check it with clay).

You should have approx 10.3 C.R. with your .060"thick head gasket (C.R. would be approx 10.8 with a .040" thick head gasket).

Jim

already checked it. I have .060 at the closest point and that is at the point where there is no squish ring in the head IE @ the exh valve aria.

jseng1 said:

Cutting your piston periphery down by .060" as you have already done should give you .040" vertical piston to head clearance with your .060" thick head gasket. So you are good to go (but double check it with clay).

Jim

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I think you have your numbers backwards :shock:

jseng1 said:

You should have approx 10.8 C.R. with your .060"thick head gasket (C.R. would be approx 10.3 with a .040" thick head gasket).

Jim

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Yes the numbers below are backwards - I fixed them in my earlier post a couple above. As long as you got it right. All these numbers give me a headache.

I think you have your numbers backwards :shock:

jseng1 said:

You should have approx 10.8 C.R. with your .060"thick head gasket (C.R. would be approx 10.3 with a .040" thick head gasket).

Jim

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bill said:

still have a ways to go as the rings have to be file fitted before I can fit the cylinder to name a few. :mrgreen:

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File fitted? What happened to that concrete blade you had poured as part of your garage floor?? :lol:

I had mine poured in 3 stages, with progressive finish for different projects - coarse, medium and fine trowel.