57 replies to this topic

[Spider]

That's them, but I bought a few sets, not expensive. Don't use a Pilot hole!!

 

I see in that ebay advert it says they are closing down? I hope not. They are a German company.

[Gr4h4m]

..... have a much less pointy "nose" so are less prone to wear,

 
I've heard that before actually and sorry, but I disagree on that. There's only ever (or should only ever) 'line' contact between the lobe and the follower. So being 'pointy' or not shouldn't have a bearing on wear.
 
For what it's worth, I wouldn't touch a Russell Cam.

Interesting, why is that, I have had fantastic results using a Russell cam.

[ACDodd]

My road cams are definitely the pointy kind. I specify Moly grease for the lobes as initial lube unlike pretty much any other a-series cam supplier. My lobes are also not tapered.

Ac

[sledgehammer]

Not doubting what you say -

 

but I was always taught no grease inside an engine , due to it  congealing / staying seperate from the oil , & clogging the strainer

 

we were always told engine oil , cam lube , or vasilene as they disperse into the oil

 

or does Moly grease mix with the oil ?

[pogie]

Snap! I found similar damage when I stripped my 1380 for inspection at 7k miles.  I did put up a thread at the time but it was lost when the site crashed a few years ago (2013ish).  I was running a MED 296 cam made by Piper, Piper followers and MED's 1.5 ration rockers.

 

IIRC.  AC Dodd posted at the time that as I had what was pretty much a race engine, the cam followers should be treated as consumables and if the engine was one of his he would change the followers at the end of every race season.  I have seen a few other cam follower damage posts on here with people running milder cams and 1.5 rockers and the blame normally gets put on the extra force from rockers for causing the damage.

 

Edited by pogie, 09 September 2016 - 04:18 PM.

[ACDodd]

It mixes.

Ac

[hhhh]

Instead of "blaming" the extra force from higher ratio rockers and getting accelerated wear, why not reduce the spring rate proportionately to suit the higher ratio?

[pogie]

Instead of "blaming" the extra force from higher ratio rockers and getting accelerated wear, why not reduce the spring rate proportionately to suit the higher ratio?

Valve bounce?

[Spider]

I've mentioned back on page 1 of this thread about Cam Lobe Taper and touched on the need to have a Radius on the Follower Faces.

 

Rather than re-invent the wheel, here's some low down from an Engine Design Manual on it;-

 

 

The Followers are off-set axially, from the Centre Line of The Cam Lobes (or should be in this design), so as the Camshaft spins, it also causes a spinning of the Cam Follower.

 

All the Lobes (on these engines) from the Factory were Tapered the same way, ie, the smaller side being on the Pump End. This causes a Thrusting of the Cam towards the Sprocket End and this is why I've said and maintain with these Cams, as long as there is some end float, what it is doesn't matter.

 

It appears that AC's Cams work in a different way to this, that I don't understand so I'll leave that for AC to comment on. I know he's mentioned he is concerned with getting the end float just so and given his Cams don't have a Taper (and so presumably no thrust) I can see why this is important on these type of Cams.

 

I too prefer to use Molly Grease on these parts for initial lubrication until they are 'bedded in', but I only use a lick, I don't cake it on for the very reasons that sledgehammer touched on.

 

In regards to those Russell Cams, as Mini13 pointed out, they have a more 'flatter' nose to give them more 'dwell'. This shape has by it's very nature very fast Opening and Closing Rates, ie very steep Flanks on the Cam. This means that heavier than would otherwise be required springs are needed to cope with these high rates and it also has been proven that it causes Cam Follower Failure, particularly at Moderate to Higher RPMs, as well as accelerated Cam Train Wear. In other words, while they may give (and this is highly debatable) some added power, don't expect any real life from the Valve Train.

 

They re also not hardened following re-profiling, though this has been done in an attempt to coff coff extend Cam Follower Life.

 

There's far better ways of achieving a better result. There are way better Camshafts around than these, not just for Valve train Life but also in terms of overall performance.

Edited by Moke Spider, 09 September 2016 - 10:46 PM.

[tiger99]

Excellent information, however that is an example of best design practice, and may not all be strictly necessary in a fairly mundane engine. If the follower is slightly convex, which it always should be although many engine reconditioners grind them flat, and the cam parallel, the follower will still rotate as long as the follower diameter is greater than the cam lobe width, which is almost always is, and the follower centre line is offset from the cam lobe centre line, which it also almost always is. So in most cases, although they are not ideal, parallel ground cams may be ok. If there is sufficient lateral offset a totally flat follower may still rotate if the cam is parallel, but getting a bit iffy...

 

But we now know what to ask for in our ideal engine build, radiused followers and taper-ground camshafts. If the demand is there the suppliers will have to do it, or lose business to those who do.

 

On the other hand, there is an argument for using roller followers, which allow a more aggressive cam profile. Those need an anti-rotation device in case valve bounce occurs and allows them to turn sideways. I have not yet seen roller followers in a Mini but see no reason why it can't be done, and probably has.

[ACDodd]

You have to be extremely careful with point loadings during break in. I decided on parrallel lobe and slightly radius follower to ensure best of both worlds. Of course not using the right initial lube and high poundage springs is a recipe for a ruined cam in the first 5 mins of running, that's be fore you have turned a wheel. It is now a practice in the US to fit much lower poundage spring on flat tappet based engines to reduce failures. Once break in complete, refit high rate springs and you are ready to roll.

Ac

[tiger99]

That is a good point. You would need to avoid valve bounce, so the revs would be kept down to something reasonable. It would seem to me that after the initial run, when the head is due to be re-torqued, the springs could be changed at that time, using the rope trick or compressed air to hold the valves closed, so no need to take the head off. Not all that much extra work, for a lot of possible benefit.

 

I will remember that for the next time I rebuild an engine, which might not be an A series.

[sledgehammer]

 the springs could be changed at that time, using the rope trick or compressed air to hold the valves closed,

 

the rope trick works well , but have had problems with the compressed air trick with small valves (not as much force on the valve head ? , esp with stuck collets)

 

a clean leather skipping rope also is easier to get in the cylinder some times than rope if it's getting old

 

both good methods - saves a redo of the head gasket

[mini13]

Moke,

 

I'd be interested to know what these better cams are, the last I looked into it the leading thinking was to get the valve off the seat pronto, and use the bigest area under the curve for a short duration as possibble.

 

in terms of roller lifters, I looked into this in depth a while back, for a block with tappet chest covers its pretty easy, as it looks like there are some bowtie followers ( indexed in pairs with link bars) that are available of the shelf form an american V8, for the normal 1275 block though it gets a lot more complicated, about the only solution looked to be Jesels keyway followers, which meant some tricky machining, and prubably fitting sleeves to the follower holes.

Also, IIRC to get anything worth while you needed to go to a big base corcle on the cam, as you get heavy side loadings on the followers due to the bearing diameter, "flat tappets" are actually better in some ways here, as you are normally dealing with a bearing radius of .75" vs the cam follower radius of about 42",

 

anyway I gave up on all that piushrod tech an got a K1200 head....

[Spider]

Moke,

 

I'd be interested to know what these better cams are, the last I looked into it the leading thinking was to get the valve off the seat pronto, and use the bigest area under the curve for a short duration as possibble.

 

in terms of roller lifters, I looked into this in depth a while back, for a block with tappet chest covers its pretty easy, as it looks like there are some bowtie followers ( indexed in pairs with link bars) that are available of the shelf form an american V8, for the normal 1275 block though it gets a lot more complicated, about the only solution looked to be Jesels keyway followers, which meant some tricky machining, and prubably fitting sleeves to the follower holes.

Also, IIRC to get anything worth while you needed to go to a big base corcle on the cam, as you get heavy side loadings on the followers due to the bearing diameter, "flat tappets" are actually better in some ways here, as you are normally dealing with a bearing radius of .75" vs the cam follower radius of about 42",

 

anyway I gave up on all that piushrod tech an got a K1200 head....

 

One can tinker around with camshaft profiles for a long while and there are some gains there to be had, that's almost without saying, however you don't get something for nothing and so while gains are there to be had in one part of the rev range, they come at an 'expense' elsewhere.

 

IMO, the power that these engines can make - as you've worked out - is all locked up in the head and in particular, the number of valves.

 

Long ago I looked at Roller Lifters but as everyone else has come to the conclusion, very hard to do and the gains for the effort,,,,,,, hmmmmm,,,,,,

 

I agree with what you've said re: Base Circle dia, but you start getting in to a cat chasing it's tail situation, as to get the best from that part of the geometry, the Lifter dia also needs to be increased. In fact, it's the Lifter Dia that is more of a limiting factor in getting longer dwell timings in the cam profile.  But, again, IMO, for all the effort that this all takes, it's so much easier and cheaper to fit a proper head, from which the gains to be had are lightyears ahead of anything pushrod. I've tinkered with Honda CBR Head conversions, have an 1100 one in the shed ATM that I'm doing for a mate, but it's presently down the list.