The Honda Owners Club

Hi all, Can anyone please tell me the correct plug for my 1976 CB750F1?

It has D8EA fitted (i think) and ive bought DR8ES. This is what David Silver recommends, and what is listed in the NGK book, but i cant help wondering why these "wrong" plugs are in the bike?

Out of interest i had a slight missfire on No 4, which prompted me to buy the plugs, but it turned out the inlet valve had no clearence, valve sink, common problem on bikes that have been sat for a long time as a freind who restores told me, anyone else come across this before?

Steve.

Hi Steve having just checked both spark plug types are correct

Cheers Buddy

I think the "R" in DR8ES stands for "resistor", in that the plugs have a built in resistor, which I think improves running somehow (bigger spark?).

(Witchmaster: you may know, your CX has DR8ES-L plugs, wheras one GL500 has D8EA plugs for some reason.)

Depending on the design of the valve gear, clearances generally diminish with use but I've never heard of them disappearing on their own.

Regards

Chimpy

Hi Red V Four

My CX now has Iridium Plugs Fitted .... (can't remember the number at present) and they have a much longer lifespan, improved spark, improved fuel consumption, smoother running and once the gap is set you can forget about them.

I didn't know that the GL500 had D8EA fitted as standard in the CX/GL500 manual it states that both types are used for standard use as it does in the CB750 Manua.l

I will get around to fitting them in my CB750KZ at some point too.

I should have looked it up before I posted! It's just some US models that have D8EA plugs, most have DR8ES-L.

As to Iridium plugs, yes that's the hype, but I have heard they are a waste of money on "lower performance" bikes,(no offence to the CX) and that they really don't have all that much effect on performance or economy. They do last longer, but as they cost a heck of a lot more, I should expect so! A bit like using fully-synthetic oil in a Superdream.
My CX should hopefully be at Gaydon on August 24th, so I could show you mine if you'll show me yours...............
The Viffer can stay at home for a change this year.

If you shop around Iridium Plugs are only twice as expensive as "Normal Plugs" but last 3 or 4 times as long so in the end cheeper regardless of whether or not they improve performance etc: I cetainly noticed a difference in my CX However.


cheers Witch

Really? Let me know some time what grade they are then, please. I suppose I could look them up somewhere though......

There is a power seller on ebay selling them at 5,95 a plug which is the cheapest I have seen anywhere and his postage isn't bad either.

I found them searching for parts for my CB750K (same plugs as the CX)

Cheers Witch

Thanks Guys,

I'll fit the ones i bought. I am still struggling with the pilot jets, i have resorted to Cellulose thinners as someone suggested earlier. I am going out in 10 mins to check how the 'overnight soak' has done,

Will keep you posted!

Smudger.

I got a full set of brand new Honda recommended NGK's for my CB550 for £5.25 (inc p & p) from Ebay.

They work fine and with the mileage I do they'll last me several years.

Well, no use with the thinners, i've taken the jets to a local garage who has an ultra sonic cleaner bath, he reckons a couple of sessions in there and thry will be like new. I pick them up next Thursday......

Chimp Boy wrote:Depending on the design of the valve gear, clearances generally diminish with use but I've never heard of them disappearing on their own.

On SOHC engines the clearance opens up as the components wear - quiet top end = good.

On DOHC engines the opposite happens (think about how the bucket and shim works) - quiet top end = bad!

My Sprint was really quiet until the valves were done at 24k miles. All 6 were tight. Now engine has a noisy top end (= good...)

A lot of factors effect the poor old valve clearance. The valve material, the seat material and the camshaft profile (more radical cams with faster accelerating ramps) and the operating rev range of the engine all effect the rate of wear of the valve and its seat. So it's fairly safe to say that some wear will take place at this point during the lifetime of the engine, diminishing the valve clearance. Combatting this on an engine which uses rockers is wear on the camshaft lobe, the rocker pivot and its two contact surfaces and of course the valve tip. This wear can add up to more than the valve seat regression so the clearance increases. With camshafts directly operating the valves via a bucket and shim there is less opportunity for wear and normally the only item that can show any is the camshaft lobe itself. The adjustment shims are generally very hard and I've hardly noticed any wear when I've measured them after taken them from high mileage engines. If the camshafts oil supply is good the wear again can be minimal so if valve seat regression is high the clearance will reduce and you will be in trouble.

When I build an engine with directly opening valves I always put in shims that give clearance at the top end of the range. With a rocker operated valve I normally set the clearance half a thou up on the recommendation. If the engine is using a high lift long duration cam I often set the clearance up to one thou larger.

A tappett that you can hear is not necessarily a bad thing. The quite ones that burnt the valves out on one of my 750s were much worse.

Regards

Chris