Kent x-flow tappet improvements anybody?

[dikko]

What can I do to my tappets (legally) to improve valve clearance etc for better performance on a FF Kent engine??? Anything?
What is done ILLEGALLY come to that!!! (I'm intrigued - honest!).

[jonners]

It's not an improvement to the valve clearances you want but different cam timing, using the same cam. This can be done by using different clearances but is not practical.

You could take a leaf out of Colin Chapman's book and reprofile the cam followers but the machining is very difficult and is probably not on under the regs...

[zefarelly]

what difference would the followers make ?

rocker arm ratio may change the effective cam movement but followers just go up and down ? given they're a 'limiting factor' within the engine design I would recommend doing anything to them myself.

incidentally, 2 years racing on an A6 " 8k limit and the cam looks like new but theres wear on the followers

[Al Weyman]

I agree with Zef apart from maybe lightening them to get less valve float for a given spring pressure but bet you wont notice the difference!

[JamesH]

Grind down the followers to lighten (then polish of course). You can also reprofile the end of the rockers (on valve end) to give better lift of the valve.

And the legality depends on what the engine is in of course.

James

[jonners]

am probably in deeper water than i intended here, but if you reprofile the follower you can make the cam lobe and follower work together in a way that changes the cam timing - not much point if the cam is free in the regs but it's controlled in FF - or maybe the cam timing is controlled so it's not on

it wouldn't be easy, the machining would be horrendous and the set up and experimentation would be a nightmare but Chapman did it once and had everyone baffled for ages whilst his cars kept winning by a country mile but i do recall in the book where it's mentioned that the machining was very difficult

Usual apologies etc if i've misunderstood, need to get my coat etc etc..

[zefarelly]

hmmm . . . maybe the block was bored to alter the angle the followers sit in it? I fail to see what difference the followers actual dimensions would make

the rocker trick is well known I think, I've never bothered as cams are free for me, reliability isn't, so the stronger the better

I suppose titanium followers might save weight, but thjats getting silly, you might as well buy a different engine !

[jonners]

but if, say, the face of the follower was machined as a dome rather than left flat...??? Perhaps when I said reprofile the follower i used the wrong word

Granted would only make a small difference and sorting a cam profile to suit wouldn't be straightforward but Chapman did it (albeit with an Austin 7 engine - but the principle is the same)

Definitely one to file under 'nice idea but no further action'....

[GORDON STREETER]

Just a quick word about tappet settings. If you alter the settings much from the cam manufacturers there is a danger that you will clap out the followers ,because the cam has an opening and closing ramp the setting is designed to do just that. Offset dowel the cam to play about with the timing . It wont make huge amounts of difference but all the best Kent FF engine builders do it, along with obtaining max lift by playing about with and swapping rockers. Collectively with everything built decently a blueprinted engine can give a bit more power. I dont know how long you have been racing ,but dont believe that everybody has a lot more power than you. And you will nomally find that its the backmarkers that have cheating engines. In one make races its mostly the front runners that get checked !

[esper]

zef, titanium in a steel block , don't try it. Titanium and steel are not close friends

[dikko]

Thanks you Guys, was just wondering.... FF is controlled cam etc so cant play around there.....it's just I overheard an engine builder say recently that he could legally do something in that area and I wondered what - short of altering the tappet fulcrum (illegal and difficult I'm sure) and as you say, profiles, I wondered what else he may have up his sleeve......

[JamesH]

Originally Posted by jonners

but if, say, the face of the follower was machined as a dome rather than left flat...??? Perhaps when I said reprofile the follower i used the wrong word

I think that as new, Ford followers are domed (I think it makes them rotate in use to level the wear out). In use they go flat, then concave as they wear down. Most after market followers are flat. I grind my concaves flat, match weight, then polish.

James

[GORDON STREETER]

JamesH
You are right , cam followers do have a large radius so the cam doesn't hit them in the middle, causing them to spin, also the pushrods spin as well .
I don't hold with grinding them down. I would think thats a recipe for disaster
and a new set are peanuts, I dont know what you do for a living , but I happen to work with engines all day long , the last of the Fiesta / Ka pushrod engines are terrible for follower problems ,and once through the hardening wear out very fast then snap off and often smash the block !

[Locost47]

James - a couple of Locosters with engines from the most common supplier had engine failures and traced it back to lightened cam followers. It got a bit messy and neither of them went back.

You get your engines from the same source, but perhaps he doesn't do that any more or at least doesn't take them as far now. Also my own personal view is that they are illegal in our series, under the clause about no other modifications other than those specifically desribed in section 5.7, which only mentions the followers in passing as being provided by Kent with the standard cam. It doesn't say that you have to use Kent's, but neither does it say anything about being allowed to lighten them, ergo you can't. Some people obviously read that bit differently, however.

[marcush.]

I worked on an A-serie engine the other day ,which is designed along those lines...i had quite tricky followers i found in the states wich solved the pitting problems on the Cams and lowered oil temps dramatically.Power went up as well. I could possibly put you in contact with the guy.
Then there is the pushrod theme .Make sure they are arrow straight or have conical ones made ,this reduces flex in the valvetrain.You can learn a lot in US Racing as those use pushrod engines still...

[Robyn Slater]

I believe the cam profile is ground at a slight angle to the axis of the cam to cause the follower and pushrod to twist. The large radius ground on the base of the follower helps to keep the two contact faces alligned.

Zef, If you realligned tappet bores at a different angle you would reduce the ammont of lift at the pushrod.

Hope this makes sense.

[JamesH]

Originally Posted by Locost47

James - a couple of Locosters with engines from the most common supplier had engine failures and traced it back to lightened cam followers. It got a bit messy and neither of them went back.

You get your engines from the same source, but perhaps he doesn't do that any more or at least doesn't take them as far now. Also my own personal view is that they are illegal in our series, under the clause about no other modifications other than those specifically desribed in section 5.7, which only mentions the followers in passing as being provided by Kent with the standard cam. It doesn't say that you have to use Kent's, but neither does it say anything about being allowed to lighten them, ergo you can't. Some people obviously read that bit differently, however.

I had heard about some follower failures in that way, not sure whether my race engine has the 'mod' or not. One bloke said that the follower that failed appeared to be cracked before he used it, but 'builer' recomended he use it anyway. Engine failed, but I think supplier replaced broken bits FOC - not sure though.

I look on it like this. When you take apart an old engine, the followers you take out are pretty worn down (about 2mm or more thinner than a new ones that come with a new kent cam which are not to Ford spec anyway because they are flat faced). They are always concave by that stage. And they are legal I beleive....they must be because they are just worn versions of the ford original. Grinding off the concave and polishing makes them closer to the Ford spec follower, I woudl think anyway.

Its perhaps something that should be brought up in the AFD?

James

[Locost47]

Yeah, i think this could come up at the AFD. I doubt there's a lot of additional performance being gained from it but apparently some of our guys are regularly revving their engines to 8k and "allegedly" one of the main front-runners uses a 4.44 diff everywhere, which means he'll be revving the knackers of it at Thruxton.

I see what you mean about the Kent followers not being to Ford spec but neither is the cam, to be fair.

Some interesting gossip i heard recently is that people have been exploring variations in cam timing from what Kent recommend and that 115 degrees is now the favourite for high-rev power. Could just be gossip though.

*Apologies for hijacking the thread, by the way*

[GORDON STREETER]

I can confirm that the Kent cams are ground with a taper and their followers have a radius . Valve bounce is a killer for followers apart from everything else including cold starting and valve springs to strong for the job!

[zefarelly]

good point marcush ! I agree with Gordon, followers are cheap, ( 20 quid a set) so fit new ones, and they are ground with a 6ft radius or something, to make them rotate and the lobes are angled

re springs, I think the VS 39's Kent recommend are too heavy for my engine, although this is something I know little about . . .

[JamesH]

Originally Posted by Locost47

Yeah, i think this could come up at the AFD. I doubt there's a lot of additional performance being gained from it but apparently some of our guys are regularly revving their engines to 8k and "allegedly" one of the main front-runners uses a 4.44 diff everywhere, which means he'll be revving the knackers of it at Thruxton.

I see what you mean about the Kent followers not being to Ford spec but neither is the cam, to be fair.

Some interesting gossip i heard recently is that people have been exploring variations in cam timing from what Kent recommend and that 115 degrees is now the favourite for high-rev power. Could just be gossip though.

*Apologies for hijacking the thread, by the way*

Hi Rob,

Well, I think I hit 8k once by accident - still have the dents in the top of one of the pistons to prove it.....hard to believe a stock Xflow 1300 can do it regularly.

Cam time changes are such a PITA though without verniers - I have a set of offset dowels, but have never been able to get the old offsets out to change anything. Would be much cheaper to allow verniers timing rather than offset dowels. Never undestood that rule, although now that people are taking the time to use offsets, perhaps its time to reconsider the rule.

With regard to followers - there should probably be a rule change to specify the minimum dimensions of the top hot brim bit.

James

[RTH]

You might talk to Burton Performance at Ilford. There are a range of after market modifications, roller rockers in aluminium ,steel shafts, low friction spacers, special push rods etc

The very latest Ford KA and SportKa models have a heavily revised rocker gear with I think needle roller bearings but I have never had one apart.

[GORDON STREETER]

JamesH
I dont know how much you paid for a set of offset dowels but they are certainly cheaper than a vernier duplex chain set up ! The standard dowel as fitted from new is an interferance fit, and the only way to get them out is to seriously tighten the dowel up in the vice and twist the cam. All the offset dowel kits are a loose fit, otherwise you couldn't assemble it ! Obviously you can't use STD or HL roller rockers in your engine ,but I would have thought that you can alter the valve timing . Although I don't know the Locost regs.

[StephenRae]

It's common practice to assemble the cam without the dowel...it doesn't move!

[Dennis.Doyle]

Sorry, no idea what FF engine regs allow you to do as I don’t do FF, except that they used to get more stringent every year as they explicitly banned each new mod. However, I have played with xflows.

A reputable engine builder once advised me to first ensure the rocker was horizontal when the cam was at half lift. I think was just good engineering practice to ensure the contact patch of the valve stem never reached either edge of the rocker pad which is a possibility with either a high lift cam or rockers operating at a “drunken” angle. You could adjust this by raising/lowering the rocker fulcrum point by shimming/grinding the rocker posts, but you’d want to be sure the rocker shaft holes were still in line. Also, I’ve noticed that some of the after-market solid posts are different heights too.

BTW the only rocker shaft I've ever broken was one of those "high strength" competition ones - the standard ones didn't do that!

Reprofiling the rocker pad would change the effective rocker ratio but not by much & anyway it could mean the contact patch moving off the centre of the valve stem which would be a bad idea for friction & wear. FF engine builders certainly used to machine the follower pads, but (& I’m guessing here) that was either to ensure they were perfectly in spec or as symmetrical as possible?

According to David Vizard writing about minis, lightening the followers, pushrods & rockers would only raise the limit for valve bounce by 40 rpm, i.e. not worth the bother given the potential for unreliability. Having nothing better to do on winter evenings I ignored this, got hold of some shorter (1500 pre-xflow) pushrods & lightened & polished my rockers – well at least they look prettier & it costs almost nothing!

I think each individual bit of blue printing gives “trivial” incremental improvements but it adds up so the sum total is a Cortina GT engine producing ~110bhp.