base gaskets to lower compression
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Stage III
Joined: Mar 2024
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From: nor-cal
base gaskets to lower compression
New to the forum as of today. Putting my 73 flh 1200 back together after a considerable time in storage. After having a sparkplug hole with insert blow out in the 2000's pulled the heads off and saw some scratchs in the cylinders. Well it's been 16 years and lots of stuff happened in life, but here I am. Pulled the pistons and saw more damage to the skirts than I expected, got a new set of Wisco 9 to 1's (same as before, just 10 over) and am now getting ready to re-install them. Bieng a kick start only I thought I ight drop the compression a hare by installing thicker base gasket or shim, but I'm having trouble finding what I am looking for if it even exists. From what I've found the typical base gasket is around .020, found one that says crushed is .025, was hoping for maybe a .010 shim? or just a thick metal gasket with a crush of .030 or .035. Is there such a thing?
Road Master
Joined: Mar 2012
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From: Ohio
Cometic makes 0.031" thick base gaskets.
Are you installing new pistons with the cylinder bore damaged? Or did you get oversize pistons and having the cylinders bored?
https://www.denniskirk.com/cometic/h...prd/266232.sku
https://www.denniskirk.com/cometic/f...prd/266231.sku
FYI, you can most have Cometic make some steel shims for use as stroker plates. It takes about 0.060" increase or decrease on a stock bore Shovel motor to change the compression by 1 point. Maybe you should just get 8:1 pistons and sell the 9:1 pistons.
Are you installing new pistons with the cylinder bore damaged? Or did you get oversize pistons and having the cylinders bored?
https://www.denniskirk.com/cometic/h...prd/266232.sku
https://www.denniskirk.com/cometic/f...prd/266231.sku
FYI, you can most have Cometic make some steel shims for use as stroker plates. It takes about 0.060" increase or decrease on a stock bore Shovel motor to change the compression by 1 point. Maybe you should just get 8:1 pistons and sell the 9:1 pistons.
Last edited by Ohio HD; Mar 28, 2024 at 09:14 AM.
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From: la la land jerzey
Maybe if you bought the correct pistons on the first place - we electric start its 8 1/2 to 1 electric start 74 inch — 7 to 1 kicker only — 80 inch 8 to 1
we have the liberal gas to today - its mostly fake - it has. Alternative motive its better for the environment ya right - and of corse you pay more for less
we have the liberal gas to today - its mostly fake - it has. Alternative motive its better for the environment ya right - and of corse you pay more for less
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Stage III
Joined: Mar 2024
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From: nor-cal
When I built the engine originally in 1991 I had it balanced with 9 to 1 Wisco at .050 over bore, so I got another set of Wisco 9 to 1's at .060 over, and had the cylinders bored. Wanted to keep the same weight, or at least as close as I could. I daily rode the thing kickstart only for about 20 years like that. Thing is now I'm 58 years old and weigh about 30 pounds less than I used to, just wanted to add about .010 to the base gasket thickness to drop it a bit. on Vw engines we would almost always run shims to drop the compression for street drivability and that is what I had in mind, especially with the quality of pump gas these days. Also, where is the best source for shovel engine parts? Looked at Dennis kirk and J and P and some of their prices, for presumably Chinese junk, was through the roof. Thanks in advance!
Club Member
Joined: Mar 2009
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From: Niles Canyon Ca.
When I built the engine originally in 1991 I had it balanced with 9 to 1 Wisco at .050 over bore, so I got another set of Wisco 9 to 1's at .060 over, and had the cylinders bored. Wanted to keep the same weight, or at least as close as I could. I daily rode the thing kickstart only for about 20 years like that. Thing is now I'm 58 years old and weigh about 30 pounds less than I used to, just wanted to add about .010 to the base gasket thickness to drop it a bit. on Vw engines we would almost always run shims to drop the compression for street drivability and that is what I had in mind, especially with the quality of pump gas these days. Also, where is the best source for shovel engine parts? Looked at Dennis kirk and J and P and some of their prices, for presumably Chinese junk, was through the roof. Thanks in advance!
Road Master
Joined: Mar 2012
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From: Ohio
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From: la la land jerzey
Harleybalance is an rpm thing lets say 2700 rpms its smooth and riding it hi way its fine after a complete overhaul and re balance
changing the pistons at a later date to unknown weights - just know the pistons never weigh the same anyway - the smooth spot in rpm chages only
V twins in single crank pin assemblies rotating mass is huge so the smooth is on a scale of rpm in location - as in and out of balance smoothness is how they work
unlike a car engine the balance is along the rpm line in speed of rpm - faster you spin it the more it vibrates when out of balance - reason fluid dampeners work on a race engine and not a Harley
changing the pistons at a later date to unknown weights - just know the pistons never weigh the same anyway - the smooth spot in rpm chages only
V twins in single crank pin assemblies rotating mass is huge so the smooth is on a scale of rpm in location - as in and out of balance smoothness is how they work
unlike a car engine the balance is along the rpm line in speed of rpm - faster you spin it the more it vibrates when out of balance - reason fluid dampeners work on a race engine and not a Harley
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