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View Full Version : Can tappets cause misfires?



Wobba
23-03-2009, 10:28
I know some engine designs they can, but not sure about F7R's.

I have a subaruesque warble from my exhaust and very loud tappet noise. It seems to have a misfire when the tappets are playing up...

Flash Arghhh
23-03-2009, 11:13
Suppose if one was sticking down but then that would cause the piston to hit the valve, wouldn't it? :?

Wobba
23-03-2009, 11:16
Suppose if one was sticking down but then that would cause the piston to hit the valve, wouldn't it? :?

Fookin hope not!

MAXIBOY
23-03-2009, 12:37
no....

if they tap then the slack is not being taken up by the oil filled tappet thus you are not getting maximum valve opening lift meaning less chance of it hitting the piston and maybe a decrease in performance thats noticeable but i doubt a misfire unless there really bad

but i could be wrong..

try a compression test ..low reading would indicate poor cylinder filling..

Wobba
23-03-2009, 13:49
DROPS IN PERFORMANCE!? NOOOOOOO!

Poor cylinder filling? What's that, fill with fuel or air?

If there is incorrect lift on the valves then that would change exhaust note/beat would it now? Hence the Sccoby noise.

The tappets are EXTREMELY loud at mo.

MAXIBOY
23-03-2009, 14:04
poor cylinder filling means air in this cases as the fuel is injected in directly..

if the tappets are not working you will lose lift and duration as they wont have the correct clearance.

doubt they would cause a scooby noise though..i would look elsewhere first..

Wobba
23-03-2009, 14:29
Well I have considered injectors being a possible suspect. I may unplug one at a time later on and see if it has any effect.

If I were to replace tappets, it would just be a case of cover off, cam followers off, cams out, bash the lifters out with a hammer and replace right? Easy?

MAXIBOY
23-03-2009, 17:41
cam cover off.
timing belt cover off.
pulleys off or remove with cams.
cams retainers off.
cams out.
lifter followers out with a magnet.
reassemble with a load of graphogen patse or cam lube.
run in for 20 minutes @ 3000rpm.
oil change.

Wobba
23-03-2009, 17:52
Excellent thanks mate!

Wobba
25-03-2009, 23:48
cam cover off.
timing belt cover off.
pulleys off or remove with cams.
cams retainers off.
cams out.
lifter followers out with a magnet.
reassemble with a load of graphogen patse or cam lube.
run in for 20 minutes @ 3000rpm.
oil change.

Do I simply put the paste/lub over the cam lobes before refitting?

MAXIBOY
26-03-2009, 00:00
yes mate as the oil won't get there instantly just a precaution when just fitting new followers really better safe then sorry though..

Wobba
26-03-2009, 00:48
yes mate as the oil won't get there instantly just a precaution when just fitting new followers really better safe then sorry though..

Thank you. Another quick question: do the cams slot into their correct position (in relation to the valves) when refitting or do I have to put them in the same position I took them out. I guess it will be clear when I do it but I like things straight in my head specially when dealing with timing gear.

I think what I will do is hand crank the engine to TDC before removing old cambelt so I know where the marks should be upon refitting and so I dont damage any valves should any of the pulleys move out of place...

MAXIBOY
26-03-2009, 09:56
yeah lock the bottom end at tdc top pulleys should line up with the marks on the cam cover..

Coops
26-03-2009, 10:00
and pullies only fit one way onto the end of the cams so no worries mate, get stuck in! :wink:

Wobba
26-03-2009, 12:45
Cool Cool Cool!

I seem to remember that hand turning pulleys with the cams on is pretty hard...

cliokiz
26-03-2009, 13:44
Yeah, very hard indeed, the springs take some serious compressing so i doubt you'd easily be able to do it by hand!

Be careful when you take the cam retainers off, the cams tend to spring out as they're under a lot of pressure from the valve springs.

Should i use graphogen paste during a head rebuild on the cam lobes using the existing lifters? Or should i just splash some oil in there before i run the engine?

Wobba
26-03-2009, 14:27
From what I have read some people just use existing engine oil, or if they are doing an oil change anyway, put thicker transmission oil on them and run the car for 20 mins at 2k revs...then oil change.

Trouble is its these first start-ups where damage is most likely to occur due to poor lubrication, so I am going the paste route.

MAXIBOY
26-03-2009, 17:41
plus new cams and followers need hardening as there new

new cams and followers can destroy them selves if allowed to idle when new..should be run at 2500/3000rpm for about 20 minutes to allow them to bed in when first fitted..

after that time they are fine to run with just oil.

if i build an engine i always assemble it using graphogen paste as unlike oil it doesn't drain off..and a little never hurts as none might

best to use it when you might leave an engine a few weeks after building before fitting and using..

Wobba
26-03-2009, 18:20
Got some paste on order. Hope it arrives before weekend!

cliokiz
26-03-2009, 19:01
Whats the actual name of the stuff i need?

Graphogen paste? Can it be had from places like Halfords, Parkers, GSF maybe?

MAXIBOY
26-03-2009, 19:20
only place i've seen it and buy it from is burton the ford place..

never done a google though

Wobba
27-03-2009, 00:07
only place i've seen it and buy it from is burton the ford place..

never done a google though

Yes I have heard of Burton, but you can get it off ebay too.

Graphogen paste is the stuff, aye!

MAXIBOY
27-03-2009, 00:44
burton is a top ford place but they have a great catalogue of engine building tips and tools/books/videos etc as well..

plus i like to look and see how short changed we are on renault tuning items compared to fords..

Wobba
27-03-2009, 14:49
Yea I read one of their guides the other day, very handy!

Ok,back to subject:

I don't have a misfire as such but a weak power output from one or more piston. It sounds like a scooby, and only starts to sound like this and loose power when the ticking starts going on one or two of the tappets. The tappets dont always tap straight away and do in fact clear up a little but then come back quickly. It's very loud, Arj256 has heard it.

My new tappets have arrived but not my graphogen paste. I also have a new cambelt to collect tomorrow and a ton of oil for an oil change.

Hopefully this will solve the issue.

MAXIBOY
27-03-2009, 15:21
i hope so too mate.. :D

Wobba
27-03-2009, 16:12
i hope so too mate.. :D

Having given it some research and thought, I am sure 2 of the tappets have been jammed compressed, with no oil in them. It would mean the valves are not opening fully on one cylinder and causing the burble scooby noise and the loss of power. They must open themselves up a bit when the car is left standing, as its not bad when I start the car but it soon goes bad again as the tappets get stuck once more, from the pressure of the cams and valves...and not being filled with oil.

I'll see if I can have a look at the little oil galleys there too and see if I can clean them a bit...

Laine_16v
29-03-2009, 23:18
I got my tube of Graphogen paste off ebay, but think it was a one off.

Wobba
29-03-2009, 23:47
I got my tube of Graphogen paste off ebay, but think it was a one off.

I applied mine liberally to my cams earlier ^^ Thanks Ebay!