Hi guys,

In order to get more power, or torque out of a four stroke engine, has anyone tried grinding the profile of the lobes on a camshaft?

Some machine shops in Mexico modify stock camsafts for full size automobile engines by grinding them.

Do not modify cam in 4 stroke modelengine, 4 stroke modelengine has higher overlap than full size automobile engines. Therefore we get more power in 4 stroke modelengine than full size automobile engine in weight/horsepower and horsepower/litre.

Jens Eirik

Motorboy,

I should be more especific. The engine is a Magnum four stroke, you can tell the overlap on a Magnum is not as aggresive as on a Saito, or YS.

More comments comments please.

You could probably re-grind the stock cam, but you'd have to get it re-hardened. Then you'd need longer pushrods to compensate for the smaller base circle. Probably need stronger valve springs too.
Finding someone with the machinery small enough to do the job properly, and put the proper surface finish on it would be the hardest part I think.
Don't some of the guys racing YS's get their cams ground, or get "high Perf." cams somewhere? Seems I recall reading about that here somewhere a year or so ago?

An easier modification would possibly be to change the rocker arm ratios. By enlarging the pivot holes in the rocker arms and putting bushings in them you could relocate the pivot hole slightly more towards the pushrod. This would give you more valve lift and slightly more duration. Otherwise it wouldn't be too hard to make a new cam if you have the right machinery available. You would need a cam grinder and a gear hobber. Also, you would need to understand heat treating so as to surface harden the lobes before they are finish ground. There are lots of machine shops that are capable of doing this kind of work but the problem is finding someone that will do it for cheap. 4-stroke cams are quite complex and the only way to make them cheap is to be able to mass produce them and sell them by the thousands, like Saito, Y.S., Thundertiger and O.S. do.

Med:

Regrinding the cam is one possibility to increase the duration, another and often easier method is installing mushroomed tappets. By having the contact end of the tappet a larger diameter the valve lifts at an earlier point in the cam's rotation, and it closes later.

Before you start any modifications, though, the model 4s engines all have pretty hot cams to start with, making them "Racier" tends to disrupt the idle.

A goos example is the FA-120 Saito compared to the FA-120S engine. More power with the "S" but not as good an idle. The "S" uses a cam only slightly hotter, but it has mushroom tappets making it effectively a "Race" cam compared to the "Mild street" in the normal engine.

Pisture is the parts that are changed to accomodate the mushroom tappets, compared to the normal parts.

Bill.

This is a job for ---superwrench!
Eevn YS screwed this up so badly I could not believe it - a few years back -and they never admitted it.
the travel of the valve - must always be less than the effective closed length of the valve spring.and or keeper /guide
On the original 120, they designed in .030 over travel -so there was plenty of clearance.
then-- they reground the cam lobes to increase the valve lift --aprox--- .030.
I got one of the first of these high performance regrinds .
RickMattie was working at YS/Futaba then.
I called him -he said "no way "
I said - "check it out" -
I fixed my engines -which had the spring keepers bottoming on the valve guides - with a little Dremel work .
PS they were having problems with the cams and lifters -
surprise surprise.

Bill, check your toolbox for a pair of wire cutters or tin snips and take care of those nails




dave

It is a place for model engineer who can make cams and gearwheel..

It is true, these standard 4 stroke modelengines are more agressive than than full size automobile engines.
In full size automobiles has not big overlap, valve timing cause law about emission, pollution etc..

Why trimming standard 4 stroke modelengine when you can buy a new Saito, YS engine in local dealer.

Jens Eirik

Mi dear Jens,

Why trimming standard 4 stroke modelengine when you can buy a new Saito, YS engine in local dealer. ..... Why?????

Because it's a challenge.
Becuase I want to be different.
*Becuase leading is always better than being a sheep.

*No pun intended

Ah!!!!!

I forgot the most important one... BECAUSE IT WOULD BE SO COOL!!!!

Just imagine, a tricked out model engine, It would so much rock!


Keep'em comming guys

Don't shoot me, but I always thought the easiest way to hop-up a 4-stroke was to replace it with a 2-stroke
I've grown fond of 2-strokes because you don't need to grind any cams to change the engine's timing. Just whip out the ol' Dremel and remove some material from the ports in the cylinder sleeve.

Hate to admit it, but your're right.... I still like 4 strokes better, the throatle responce is better, they almost never die, they sound cool.

and they dont load up if properly tuned and they add that growling effect to your pride and joy.

Bill,

If you reground the cam profile with the intention of increasing valve overlap, you would have to add material to the cam ramps first. The mushroomed tappets effectively do just that by causing the valve to lift sooner and stay open longer. If you simply removed material from the ramps you would cause the valve to open later and stay open for a SHORTER duration.

Bob

Bob:

You have misunderstood. You do not cut the ramps only, that definitely would decrease the duration. By cutting the base circle you can increase the lift, if you also cut the crown of the lobe you can increase the duration and maintain the original lift.

Yes, as I said earlier, the mushroomed tappets do increase the duration without having to modify the cam lobe.

Bill.

AaaaaaH!

And dawn breaks on Marblehead!

Thanks for the clarification!
Now I get it!

Best Regards!
Bob

In doing this you would move the torque peak to a higher rpm which would in turn require a smaller prop in which case you would lose more than you gain.

Hobbsy:

As I said earlier, the stock cams are aboout as hot as is practical.

Bill.

The first time I checked the valve timing on my old Saito 150 I was amazed.

All:

I've posted this before, but I don't thnk it will be out of line to add it here.

These are specs for some Saitos I've checked. Hobbsy's little FA-30 is in here too.

The mildest cam timing here, if in your street auto, would make it a fire breather.

Bill.