|
Author |
Message |
stinkwheel |
This post is not being displayed .
|
stinkwheel Bovine Proctologist
Joined: 12 Jul 2004 Karma :
|
Posted: 14:21 - 04 Dec 2022 Post subject: Is fitting differing weight pushrods a bad idea? |
|
|
This is on an enfield bullet, so it's a 2-valve overhead valve single with two seperate cams running off a pinnion on the end of the crank. The pushrods have a "bucket" on each end which engages onto a cam follower at the bottom with an adjuster and onto a pair of bolt-on rocker blocks at the top.
It's been heavily tuned and I keep bending inlet pushrods. I've dealt with the main problem which was poor clearances between the cam and follower but on inspection today, the inlet one is again a bit bent. No banannaed like previously but a slight compound bend in a couple of different directions when you hold a straight edge against it. I suspect full-bore-roar is simply too much for it. All the other parts of the valvetrain are upgraded to performance parts anyway (rockers, valves, springs, cams)
Now I made up a set of rods out of solid 7075 round bar instead of the unspecified Indian made alloy tube of the originals. There's no way this will bend. When I put some in a clamp and tried to bend it, I found the elastic phase is outwith the confines of the pushrod tunnel. As well as it being very strong alloy. Thing is it's significantly heavier.
I'm considering using the solid rod for the inlet and a standard, lighter one in the exhaust. I doubt it'll make much difference, I suppose the inlet valve will have a tendancy to float before the exhaust one. The rods are different lengths anyway and open and close independantly so they're not a balanced system.
Just wondering if there's something I'm overlooking that would make this a bad idea? ____________________ “Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles. |
|
Back to top |
|
You must be logged in to rate posts |
|
|
Easy-X |
This post is not being displayed .
|
Easy-X Super Spammer
Joined: 08 Mar 2019 Karma :
|
Posted: 14:37 - 04 Dec 2022 Post subject: |
|
|
I suppose you could consider the push-rods to be a parasitic drain in the system like an alternator. You'd therefore want the lightest but strongest rods possible. I would imagine if it was a perfectly balanced system introducing rods of different weights might introduce some vibration... have you noticed any vibration on your Enfield?
Maybe for a perfect system you'd want to add weight to the exhaust cam lobe (or, more practically, remove weight from the inlet cam lobe) but a smooth, purring Bullet engine? Be a bit weird! ____________________ Husqvarna Vitpilen 401, Yamaha XSR700, Honda Rebel, Yamaha DT175, Suzuki SV650 (loan) Fazer 600, Keeway Superlight 125, 50cc turd scooter |
|
Back to top |
|
You must be logged in to rate posts |
|
|
WD Forte |
This post is not being displayed .
|
WD Forte World Chat Champion
Joined: 17 Jun 2010 Karma :
|
|
Back to top |
|
You must be logged in to rate posts |
|
|
Pete. |
This post is not being displayed .
|
Pete. Super Spammer
Joined: 22 Aug 2006 Karma :
|
Posted: 16:44 - 04 Dec 2022 Post subject: |
|
|
Heavier springs stands to reason you can use heavier pushrods without penalty. You could always waist or counter-bore them if the weight troubles you. Personally, I'd suck it and see.
Are you sue you have enough valve to piston clearance? ____________________ a.k.a 'Geri'
132.9mph off and walked away. Gear is good, gear is good, gear is very very good |
|
Back to top |
|
You must be logged in to rate posts |
|
|
stinkwheel |
This post is not being displayed .
|
stinkwheel Bovine Proctologist
Joined: 12 Jul 2004 Karma :
|
|
Back to top |
|
You must be logged in to rate posts |
|
|
Pete. |
This post is not being displayed .
|
Pete. Super Spammer
Joined: 22 Aug 2006 Karma :
|
|
Back to top |
|
You must be logged in to rate posts |
|
|
stinkwheel |
This post is not being displayed .
|
stinkwheel Bovine Proctologist
Joined: 12 Jul 2004 Karma :
|
Posted: 19:00 - 04 Dec 2022 Post subject: |
|
|
Thinking about it, it also bent a rod when it had an additional 2mm of compression plate under the barrel to where it is now so I don't think valves are tangling.
I think it's just accelerating that rod beyond what it can cope with. The performance cam has roughly an additional 2mm of lift against a stronger valve spring and the engine revs 1500 rpm higher than standard. There is less lift on the exhaust side.
You can see daylight through the springs at fully open, and the spring/valve kit was designed to go with these cams. ____________________ “Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles. |
|
Back to top |
|
You must be logged in to rate posts |
|
|
jeffyjeff |
This post is not being displayed .
|
jeffyjeff World Chat Champion
Joined: 02 May 2020 Karma :
|
|
Back to top |
|
You must be logged in to rate posts |
|
|
A100man |
This post is not being displayed .
|
A100man World Chat Champion
Joined: 19 Aug 2013 Karma :
|
Posted: 15:05 - 05 Dec 2022 Post subject: |
|
|
Could it be an issue with angles? The higher lift cam making a slight more acute angle on the rod?
I say this because I once spent a lot of time once phaffing about on my VW air-coooled motor with shims under rocker blocks etc.. to get the recommended angles when using a 'performance' cam. This was 16 years ago so I've forgotten the details, if not the time consumed.. ____________________ Now: A100, GT250A, XJ598, FZ750
Then: Fizz, RS200, KL250, XJ550, Laverda Alpina, XJ600, FZS600 |
|
Back to top |
|
You must be logged in to rate posts |
|
|
MCN |
This post is not being displayed .
|
MCN Super Spammer
Joined: 22 Jul 2015 Karma :
|
|
Back to top |
|
You must be logged in to rate posts |
|
|
stinkwheel |
This post is not being displayed .
|
stinkwheel Bovine Proctologist
Joined: 12 Jul 2004 Karma :
|
|
Back to top |
|
You must be logged in to rate posts |
|
|
stinkwheel |
This post is not being displayed .
|
stinkwheel Bovine Proctologist
Joined: 12 Jul 2004 Karma :
|
|
Back to top |
|
You must be logged in to rate posts |
|
|
Robby |
This post is not being displayed .
|
Robby Dirty Old Man
Joined: 16 May 2002 Karma :
|
|
Back to top |
|
You must be logged in to rate posts |
|
|
stinkwheel |
This post is not being displayed .
|
stinkwheel Bovine Proctologist
Joined: 12 Jul 2004 Karma :
|
|
Back to top |
|
You must be logged in to rate posts |
|
|
Nobby the Bastard |
This post is not being displayed .
|
Nobby the Bastard Harley Gaydar
Joined: 16 Aug 2013 Karma :
|
|
Back to top |
|
You must be logged in to rate posts |
|
|
virus |
This post is not being displayed .
|
virus World Chat Champion
Joined: 17 Aug 2006 Karma :
|
Posted: 18:32 - 06 Dec 2022 Post subject: |
|
|
stinkwheel wrote: |
There are no sillier cams. I checked. These are absolute maximum silly. The main bearing oil seal housing had to be undercut to fit them in the engine.
|
'absolute maximum silly' is now my new favourite sentence.
To answer your question though, I wouldn't have thought having different weights would matter too much, adding more weight will increase the reciprocating mass and reduce the rate of acceleration but I dont think thats much of a problem with that particular barking mad engine youve built. maybe if were talking an order of magnitude heavier it might be concerning. have you measured the actual weight difference out of interest?
Even on a bog stock one the inlet and exhaust valves are different sizes and therefore weights so the valve train is unbalanced between valves anyways.
Id be worried about taking away the almost sacrificial weakest link in the valve train but given that the valve wont kiss the piston without some heroic levels of valve float then I cant see much of an issue. is it worth making some rocker studs that are undercut in the centre to become sacrificial without ripping the thread out of the head?
Cheers
John ____________________ own: 81 xs1100g...
owned: 85 rat CG (sold), 91 GS500e (stolen), 84 gsx400f (scrapped), 81 z250 (siezed, siezed, scrapped), 83 cb250rs (sold), 84 gpz750r ratfighter (killed) 84gpz400 (sold), '80 cb650 ratfighter (wrote off) 95gsx6/12f ratfighter (killed) 91 xj900 (sold)
stinkwheel Well I just had my hands up a pigs fanny. Which makes your concerns pale into insignificance. |
|
Back to top |
|
You must be logged in to rate posts |
|
|
Old Thread Alert!
The last post was made 1 year, 140 days ago. Instead of replying here, would creating a new thread be more useful? |
|
|
|