19 replies to this topic

[IronmanG]

cam follower failure means i need to replace the MD266 that was fitted.

I could just get another MD266, but may as well take the opportunity of seeing what else is available that would work well with the compression ratio i have (..having said that, i'm not averse to skimming a little off the head if necessary..)

I'm running AC Dodds RS+ and he recommends 10:1 maximum static. I'll forward you the information he sent me Pat. Reading through what he writes about them that would have slightly more top end. What final drive are you running

Edited by IronmanG, 22 April 2024 - 06:33 AM.

[KTS]

I have also done the trigonometry session.... The formula I came up with I believe is correct up to the errors you put into it.

 

Used variables:

Piston dish (V_dish) [cc]

Combustion volume (V_head) [cc]

Gasket volume (V_gasket) [cc]

Ringland volume (V_ring) [cc]

Deck height (h_deck) [thou]

Bore diameter (d_bore) [mm]

Stroke (L_stroke) [mm]

Con rod length (L_conrod) [mm]

Intake valve closing, ABDC (alpha_int) [deg]

 

Formulas:

Lost stroke length (L_lost) = SQRT(L_conrod²-(0.5*L_stroke*sin(alpha_int*pi/180)*(0.5*L_stroke*sin(alpha_int*pi/180)))-0.5*L_stroke*because(alpha*pi/180)-(L_conrod-L_stroke/2)

 

Theoretical compression volume (V_theory) = pi*d_bore²*(1/4)*L_stroke/1000

Real compression volume (V_real) = pi*d_bore²*(1/4)*(L_stroke-L_lost)/1000

Unswept volume (V_static) = V_dish+((h_deck*25.4/1000)*pi*d_bore²/4)/1000+V_ring+V_gasket+V_head

 

Theoretical CR (CR_stat) = (V_theory+V_static)/V_static

Dynamic CR (CR_dyn) = (V_real+V_static)/V_static

 

Hope it is of use for someone.....

 

thanks for that; the lost stroke method you provided has given me some confidence the effective stroke calculation i've been using is OK

 

..not entirely sure i know what to do with the answers any more though 

[KTS]

Hi KTS - totally off track from your question, but possibly worth a thought before you rebuild.  ( forum rule 101, don't answer the question being asked }}}} )

 

 

 

You may have all these sorted to, but ....

 

 

 

What contributed to the cam followers failure?

 

Is a pushrod bent?

 

Did the lifters have proper ground radii

 

Were you running hi lift rockers. Was the geometry correct.... was a pushrod shaft just touching the outer wall at full lift?

 

Not relevant to the MD266 (that i know of) -  but if you can get hold of a Cam Doctor report for a cam - you will see quite a few quick rise camshafts make it hard on the follower ( or even recommend wider followers)

 

I have no direct experience but have heard of good reports of the AC Dodd cams, and I am sure he could assist with suggested matching CR, valve clearances, running in procedure, recommendation for followers etc 

 

I can say I highly recommend APTFast hard followers as not being made of cheese and coming to you with correct radii

 

Good luck on your build - 

 

 

these were the cam followers that were fitted

 

 

..and this is what they looked like after 600miles..

 

 

i'll admit that i assumed the followers were ground correctly and didn't check before fitting.  I can say that there's not much in the way of radius on them now though  , but whether that's because they weren't ground in the first place, or whether the issue is with the case hardening or initial bedding in process, or a combination of all 3 is anyone's guess really

 

pushrods were new and straight, as is (..was..) the 1.4:1 rocker gear that was shimmed to get the best alignment with the valves and pushrods

 

i'll certainly be checking that on the next set though...

[KTS]

 

cam follower failure means i need to replace the MD266 that was fitted.

I could just get another MD266, but may as well take the opportunity of seeing what else is available that would work well with the compression ratio i have (..having said that, i'm not averse to skimming a little off the head if necessary..)

I'm running AC Dodds RS+ and he recommends 10:1 maximum static. I'll forward you the information he sent me Pat. Reading through what he writes about them that would have slightly more top end. What final drive are you running

 

 

thanks. the RS+ is one of the cams on the list of possibilities.  any details you can provide would be really useful.  cheers

[IronmanG]

PMd