HarleyTechTalk

I have a 120ST, if I cam up to a TM 662-2 or TW408-6 do I need to change valve springs?  I plan changing lifters to S&S and most likely a S&S or P3R flywheel. Also can I use a cometic .03 gasket to get compression bump? Would that net 10.8:1 from the stock 10.5:1?


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Sell the st and get a SnS 124   

Thank you my motor cost me $4600 with a one year warranty. I'll keep it an upgrade or run it at 117hp 124tq I have now.


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I will probably catch some grief here but I going to go with Nick here . Not for agreeing with Nick but my reasons lol . The Harley engine is probably a decent engine. And it is cheaper to how ever the ss crank will cost something . I have heard the crank in the 120 is better than stock , I have no idea on that . The ss has gear drive crank. There is a reason why I went ss 124 as I thought it is a better engine . I believe the warranty is 2 years on the SS :Look at a build sheet on a SS 124 and compare. The 120 will probably make more hp than my lc 124 but I don't want any more crank problems Jim

R&R 124' long block $$$ well spent

Guys I already have a motor wasn't asking which to buy. I was hoping for some advice on upgrading mine not what you think I should have done.


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R&R or S&S motors on most resale or trade ins scare the uneducated. My harley motor that included 58TB at $4600 was a good deal and is not a bad motor and its titled to the bike. A bigger deal in my state.


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Quote from: Khaotic on July 27, 2016, 11:15:53 AM
I have a 120ST, if I cam up to a TM 662-2 or TW408-6 do I need to change valve springs?  I plan changing lifters to S&S and most likely a S&S or P3R flywheel. Also can I use a cometic .03 gasket to get compression bump? Would that net 10.8:1 from the stock 10.5:1?

you wont get quite 10.8 with a .030 head gasket. and you really need 10.8 or better for the -2 . you can get by with the 408-6 at 10.5-10.8.
you don't need new springs, they will handle 660 lift.you can use a .030 gasket with no clearance problems.
lifters are a good idea if you are going in the cam chest.
you don't need another crank. check the run out when you do cams. check it again in 20,000 miles.

Quote from: Khaotic on July 28, 2016, 07:01:03 PM
R&R or S&S motors on most resale or trade ins scare the uneducated. My harley motor that included 58TB at $4600 was a good deal and is not a bad motor and its titled to the bike. A bigger deal in my state.

Jim has had great success with the Harley engine 120 R I think . Your right the price is cheaper and if I already had it then I would go that direction. I have no real experience but I go with the folks that have .

Quote from: strokerjlk on July 28, 2016, 07:48:02 PM

Quote from: Khaotic on July 27, 2016, 11:15:53 AM
I have a 120ST, if I cam up to a TM 662-2 or TW408-6 do I need to change valve springs?  I plan changing lifters to S&S and most likely a S&S or P3R flywheel. Also can I use a cometic .03 gasket to get compression bump? Would that net 10.8:1 from the stock 10.5:1?

you wont get quite 10.8 with a .030 head gasket. and you really need 10.8 or better for the -2 . you can get by with the 408-6 at 10.5-10.8.
you don't need new springs, they will handle 660 lift.you can use a .030 gasket with no clearance problems.
lifters are a good idea if you are going in the cam chest.
you don't need another crank. check the run out when you do cams. check it again in 20,000 miles.

Thank you.  Is .03 gasket worth trouble if no head or crank work is done? Do the 408-6 cam and lifters if crank run out is in spec and retune for now.  I'll probably do comp as well. It's making a few noises.


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Quote from: Khaotic on July 28, 2016, 06:56:50 PM
Guys I already have a motor wasn't asking which to buy. I was hoping for some advice on upgrading mine not what you think I should have done.

we have many 120R and 120ST motors out there with no issues.

You could always run a thin head gasket and have someone mill the heads a little    ............. That would get you to your 10.8:1 compression! ...... Or more! 

Quote from: Khaotic on July 29, 2016, 04:54:35 AM

Quote from: strokerjlk on July 28, 2016, 07:48:02 PM

Quote from: Khaotic on July 27, 2016, 11:15:53 AM
I have a 120ST, if I cam up to a TM 662-2 or TW408-6 do I need to change valve springs?  I plan changing lifters to S&S and most likely a S&S or P3R flywheel. Also can I use a cometic .03 gasket to get compression bump? Would that net 10.8:1 from the stock 10.5:1?

you wont get quite 10.8 with a .030 head gasket. and you really need 10.8 or better for the -2 . you can get by with the 408-6 at 10.5-10.8.
you don't need new springs, they will handle 660 lift.you can use a .030 gasket with no clearance problems.
lifters are a good idea if you are going in the cam chest.
you don't need another crank. check the run out when you do cams. check it again in 20,000 miles.

Thank you.  Is .03 gasket worth trouble if no head or crank work is done? Do the 408-6 cam and lifters if crank run out is in spec and retune for now.  I'll probably do comp as well. It's making a few noises.

no the .030 gasket is not really worth doing unless you are gonna have the heads of anyway.
i have done a ton of these 120's. the best bang for the buck was. surface the heads .030 use .030 head gasket and a 660 SM T-man cam. 136/136
you could throw the 660 SM in without surfacing the heads or using a .030 gasket and it would still do very well.

Quote from: Jaycee1964 on July 28, 2016, 06:54:09 PM
R&R 124' long block $$$ well spent

agreed and customer service second to none.

Quote from: Khaotic on July 27, 2016, 11:15:53 AM
I have a 120ST, if I cam up to a TM 662-2 or TW408-6 do I need to change valve springs?  I plan changing lifters to S&S and most likely a S&S or P3R flywheel. Also can I use a cometic .03 gasket to get compression bump? Would that net 10.8:1 from the stock 10.5:1?

Khaotic... how did this upgrade go?  What combo did you go with?  Numbers please... I'm intrested in the 660SM swap out. 

  I'm interested in the results of the cam swap as well.

we have done several ST's and swapped the cam chest for the 120R set up,, works great and it's pretty easy to do..

I have not done the upgrade as yet but I decided if my crank run out is spec or better to keep cam and cc and shave head up to .03 and use a .03 cometic gasket to get 10:8-1. Then do cam at a later date when I do bottom end as well.


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