HarleyTechTalk

Hi guys i have a problem.. my brother gave me his 30 year sitting around 1975 shovel.. said it was 74ci.. he had screwed up the top end job all those years ago and let it sit... after taking the remaining cyl and head off i purchased the s&s 74 top end kit (pistons cyls heads and associated hardware) it went together fine until i go to spin it over after the heads were on and it stopped.. i pulled the front head off and noticed there is a little lip of piston above the cyl (pic) im thinking this aint good.. how can i remedy this (if indeed this is the problem i dont know.. my first shovel) near as i can tell with my cheapo claipers the piston lip is about .07 higher than the top of the cyl.. in the s&s instructions i remember them mentioning "if a base plate is used"... is there such a thing as a spacer to raise the cyls a bit? Do i have to get stock bore but longer cyls? Where do i go from here? Any help and advice will be greatly appreciated
Thanks
Rich

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Look thru the timing hole to see if there are numbers on it. You may have stroker wheels in it.

Quote from: Reddog74usa on November 29, 2023, 07:09:18 PMLook thru the timing hole to see if there are numbers on it. You may have stroker wheels in it.

Which means stroker plates will be needed

It goes back to the basic, measure, measure, measure.

Start like this. With the piston all the way up, measure accurately between points 'A' (top of the piston) and 'B' (top of the fire ring). Then with the piston all the way down, measure those two points again. Then add them together, you should be able to get a good idea as to what the cranks stroke is. As mentioned if you can get a part number off the flywheel, that's a huge help.

You can buy stroker pistons for most applications that will preclude using stroker plates. Also once the cylinder is off, check the length and see that it's 5.330" from the head gasket surface to the base gasket surface. That insures that you have a stock length cylinder.

Also, check to make sure that the threaded inserts at the top of the cylinder are not protruding above the cylinder head gasket surface. If they are, that can cause issues with head gasket sealing. A machine shop can make shallow counter bores to clean that up if needed.

Also check the threaded inserts in the heads to insure they're not protruding.

I'd venture a guess you have 80ci stroke flywheels at 4 1/4" stroke, and pistons for a 74ci 3 31/32" stroke.

When you put 1200 pistons in a 1340, the piston would give the exact scenario you are in; because the wrist pin height is different.

I'm betting it has 4-1/2" wheels. The piston looks to be "around" 0.250" out of place.
4-1/2 - 3-31/32 = 17/32 / 2 = 17/64  or 0.265".

84" was a very popular motor setup for guys that wanted a smooth inexpensive stroker. I think they had cast piston options back then as well.

S&S still has forged stock bore stroker pistons.

Im thinking you are right 98s1lightning... i am pretty sure that i have the 4 1/4 stroke.. ive checked the pn on the old cyls and they end in 66 (74ci) but the pistons and cyl bore appear to be 3.5".. i took off the cylinder to compare the wrist pin to top ring landing space and the original pistons appear to be alot closer to the rings than new ones and i read somewhere there was a difference.. that the 80 were higher.. so if that is correct what are my options? Have new cylinders bored out to accept 80 inch? Can i just use new 80 inch cyl and pistons? And if  i do use 80's will they fit my new heads or do i have to have the heads machined to accept the new 80 inch cyls? And will i be able to use my old base studs? I read 80ci have a thicker base... i REALLY appreciate all your guys help
Thanks
Rich

Dogbone45acp are these the ones you were talking about? Will they work with a 4 1/4 stroke?
Rich

All pistons for 74 to 80 are the same. Rod length was changed. So a 74" + .060" is 3 1/2" . 

Quote from: JSD on November 30, 2023, 08:57:58 PMAll pistons for 74 to 80 are the same. Rod length was changed. So a 74" + .060" is 3 1/2" .

I think you mean the cylinders are the same length at 5.330". Connecting rods from 1941 to 1999 Big Twins are all 7.440" long. So to make the 74" to an 80" the stroke was lengthened from 3.9688" to 4.250", and the bore as you said, from 3.437" to 3.500'.

Without determining the actual stroke in that motor, buying pistons again is just a poke in the dark.

What Ohio said. You must know the stroke before ordering pistons. The S&S Vintage catalog has information on the pistons they offer.

Sorry i was thinking of 74" pan & shovel pistons being the same. Also stroker pistons .

If the stroke is in fact 4.25" pistons are available from several sources. But your cylinders will need to be bored and honed to fit 3.5". Double check the stroke.

Pull the timing plug on left side of engine, and check for flywheel ID markings. Post a pic.

If you have 74ci pistons now, and OEM flywheel markings, its got an OEM 80ci crank in it

Post more pics 

1.300" on 80ci piston from center of wrist pin to top of piston surface (imagine piston is flat top and measure it that way. Not the top of the dome surface).

Wrist pin is 0.791" so half of that into your math equation if you need to measure from top of pin bore to top of piston

I never used copper head gaskets, bu like Ohio said, check your head bolt inserts to make sure they aren't protruding. Your picture shows witness marks where the inserts smushed into the copper gaskets.....unless they are made that way because of this common problem with the old castings.

Also check your wrist pin circlips, I wouldn't run with my clip ends in the pick groove like you have. Higher risk to spit a clip and wreck the engine. Rotate the clip so the opening of it is pointing DOWN in the same direction of piston travel........if you have them installed indexed like a "C"' (opening perpendicular to piston travel) the intertia can make the clip come out when the piston changes direction at the top or the bottom of the stroke. 

Tech tip for for ya.

Best of luck man. The old bikes aint easy!

Very important clips are seated in their grooves too

And keep everything as clean as possible, I'm seeing some contiminants in the oil on that piston?

Try to get pistons that weigh close the old ones. You don't need forged pistons in a close to stock motor.