Dyno Cams 255 OHV pics (HS40)

markus

markus

Well-Known Member
#21
#21
I thought the larger lobe was on the exhaust side for the flyweight style compression release. I always find them on pre 1970 engines, and yes you would need the longer lifter to go along with the later more conventional style cams if you swap it over

 
J

jretro

New Member
#22
#22
Base circle is the round part of the cam lobes. that's where you check your valve lash when the valves are closed. I bought a few of the Tecumseh billet rods off EBay hoping they would fit in the HS Tecumseh's no go... to long and wide.. must be for the H50's. I've heard the Billet rods for the ohv engines will work in the HS engines... anyone try this yet?
 
markus

markus

Well-Known Member
#23
#23
:laugh: I just reread what I wrote above....It IS the intake that has the comp release DUH :doah: I have an H25 and 2 H35's cracked open on the bench right now, I got "exhaust on the left" on the BRAIN right now :eek:ut:
 
cdoublejj

cdoublejj

Member
#24
#24
jretro said:
Base circle is the round part of the cam lobes. that's where you check your valve lash when the valves are closed. I bought a few of the Tecumseh billet rods off EBay hoping they would fit in the HS Tecumseh's no go... to long and wide.. must be for the H50's. I've heard the Billet rods for the ohv engines will work in the HS engines... anyone try this yet?
Click to expand...
You can buy a billet rod on the OldMiniBikes web store that fits the HS50 and HS40.

Do I need a longer lifter? every thing seemed to have fit fine for me, i didn't check valve lash or any thing.
 
cdoublejj

cdoublejj

Member
#26
#26
jretro said:
Thanks for the info on the HS rod. You're good to go with the lifters. My cam has a compression release built in and Yours doesn't .
Click to expand...
The 2mm over piston i have has Dyke ring style compression rings supposedly it makes it a little bit easier to start. good like finding one, i bought t the last one from the black widow web site. Saw one on eBay fora short while wasn't listed as such but, them odel/partn umber o nthe side was the same as mine. you can see said piston in my thread, http://www.oldminibikes.com/forum/tecumseh-engines/86860-70s-hot-rod-tecumseh-build.html

you want this rod, ARC Billet Rod Tecumseh 5.5 OHV 3.484
 
ole4

ole4

#27
#27
I just finished degreeing the Dyno 245 Tecumseh cam I installed in my HS50. Was milder than I thought with a .05 duration of 216 on the intake and 220 on the exhaust. My intake clearance is .009 and exhaust .006 so that might explain the difference. Here is what I measured

IO 29 BTDC EO 72 BBDC
IO@.050 2 BTDC EO@.050 39.5 BBDC
ICL 109 degrees ECL 110
IC@.050 34 ABDC EC@.050 TDC
IC 61 ABDC EC 30 ATDC
 
ole4

ole4

#28
#28
By comparsion the isky cam had about .266 lift and .050 around 228 and it runs well but you would not know it has a cam in it. I did however have issues after that motor was built with the root cause being the original CDI which was replaced with a stens china CDI. I have a motorsports H50 coil which I am going to try on that motor to see if it makes any difference. For my rupp continental build I think this cam will work out great.
 
ole4

ole4

#30
#30
I did not say that the isky did make more power than stock but I changed a lot of things at once. I have not assembled this engine yet so I have no idea how it will run.
 
ole4

ole4

#31
#31
My intent with the timing was to give everyone interested the data a .050 lift so the dyno 245 cam could be compared to the isky cam. Isky measures at .050 lift where dyno was at .006 lift.
 
H

Havasu Dave

Moderator
#33
#33
cdoublejj said:
JESUS!!! that's WAY less lift. I'm not sure that is a good thing.
Click to expand...
He's talking about the lift where IO IC and ICL where measured for comparative purposes. Since Isky uses .050 lift for the cam numbers, he had to use .050 lift for the Dyno, instead of the .006 lift they use on their cards.
 
J

jretro

New Member
#35
#35
I bought one of the Dyno 356 cams. It has a lot bigger lift. Had plans for a HS50 with a ARC Billet rod and the Dyno cam. Would the valve train be over taxed? How about Briggs Raptor valve components?
 
ole4

ole4

#37
#37
Yes it had a magneto and I am replacing it with a lighted magneto with aluminum lighted flywheel. One other thing the dyno cams have not compression release so once I get it together I will see how hard it is to crank. I had to do a cleanup mill of the deck to clean up corrosion of the cast in valve seat area so now I have about .009-.010 of piston pop up. Might have to pull it past compression then give it a hard pull and let the flywheel inertia help it start.
 
cdoublejj

cdoublejj

Member
#38
#38
jretro said:
I bought one of the Dyno 356 cams. It has a lot bigger lift. Had plans for a HS50 with a ARC Billet rod and the Dyno cam. Would the valve train be over taxed? How about Briggs Raptor valve components?
Click to expand...
This is my question as well!!! If the 255 is milder than we though i wonder if the 365 would fit the bill. I wonder if they are are sold out or if any 365's are left?
 
ole4

ole4

#40
#40
365 lift cam may require increasing clearance on the head or the valve may hit the head. I am actually happy with the 245 as it is 22 degrees more duration than stock and .045 more lift. I am sure the 255 will be better more like the isky grind.
 
You must log in or register to reply here.
Top