Knocking 1275

[artrider50]

I have the trusty 1275 modified with manifolds, exhuast, cooper S head etc. In one foul swoop I recently changed the thermostat, filter king regulator and added high lift 1.5 rockers.

I have also cahnged the rocker cover to give increased clearance. Now the dilema is..... when the temparture guage indicates the correct running temprature there is a mechanical sounding knocking, it doesnt happen when cold and when the car is stopped and the engine revved it is not as audible.

One suggestion is that it is pinking, but there is no overun. is this possible or has anybody got any idea's?

Cheers Chris

[daniels917]

Re: Knocking 1275

What cam have you got in there? on some of the highly tuned minis a set of high lift rockers along with a wild cam could cause the valves to hit the piston crowns, so the pistons had to be pocketed ( see paddy hopkirk's tuning your mini book) hope this isnt your problem but it might help all the best Merv.

[amalgamated users from prior forum]

Re: Knocking 1275

Message originally posted by: chri
Hi Merv, it is a standard Marina cam, but the head appears to have been skimmed a couple of times, if it was the valves hitting the crowns would it do it all the time as opposed just when it was at running temprature?

Thanks for your help.

Chris

[macdonald.dm]

Re: Knocking 1275

Hi Chris. 'Pinking' is a very distictive sound - more a 'tinkling' sound than a regular metallic knock. Also, pinking usually occurs under load, especially if labouring your engine.

If your sound is regular, then it's almost certainly something contacting that shouldn't be! I think the valves contacting the pistons is a strong possiblity since you mention the head's been skimmed acouple of times...

As you'll know, metal expands with heat, and valve stems are no exception - hence they'll touch when engine is hot.

Are thicker head gaskets available for your model? - I'd imagine they would be since they are usually recommended for head skims beyond a certain amaount (when the skim is required for curing warp as opposed to desirable for increasing compression ratio).

I guess the first thing is to remove the rocker cover and look carefully for any contact in there.

[macdonald.dm]

Re: Knocking 1275

If it isn't a rocker touching the rocker cover, it might be worth taking the car to a mechanic of the 'old school' variety who could probably diagnose the cause just by listening - do you know of anyone like this nearby?!

Something I haven't actually tried myself but read about often, is to use a metal rod or similar to act as a kind of stethoscope - press one end against your lughole, and touch the other on various engine parts; rocker cover, head, etc. You should be able to focus on different sound sources using this.

Another thought; if you place your hand on the rocker cover, can you FEEL anything making contact that's synchronised with the knocking sound?

[dogoncrazy]

Re: Knocking 1275

Installing Hi lift rockers with a skimmed head can pose problems with the valve train geometry.Check that the spring coil is NOT touching the rocker pillar.Spacers may be needed under the pillars to bring the unit back to it's correct position [or shorter pushrods].I'm also assuming that you did'nt install the rocker on the old shaft and pillars as this is a definate no-no.Also skimming the head reduces the chamber capacity and raises the compression ratio,any skimming requires reworking the chamber to bring the compression back to a suitable level or detonation will almost certainly occur with today's fuels.
Sorry that this sounds so negative but simply bolting go faster bits on in the hope of increasing horsepwer invariably falls short of expectations.For an in depth look at what's involved you need to read David Vizard's book on tuning the A series-you might be surprised-I was!!

[artrider50]

Re: Knocking 1275

Thanks guys all good advice, I reckon it is going to be a case of stripping the head off and thicker gasket, I cant see pillar damage and the head has double springs so I dont suspect coil bind.

[FranklinLeicester]

Re: Knocking 1275

Changing the suject slightly, did you get anyehere with the idea of a Maestro conversion to in-line use? As this A+ engine had 68 bhp as standard I think it would make a good unit "as is". PS How about the SEMS meeting on Sunday.

[artrider50]

Re: Knocking 1275

Hi Franklin,

SEMS could be on the cards I was due to go out on the boat but the weather is not good, where is the venue and what time.

2.00 oclock moment this morning I made up spacers that went under the pillars when I fitted the rockers, geometry is ok, so it sounds like valves hitting teh piston. Ouch!!!

Maestro Conversion is still on teh cards as I have the brand new engine sitting in a barn, two options with it, first is to change the crank and have an adaptor made to fit the marina bell housing and the second is to investigate the rear wheel drive volkswagen passat etc to see if the gearbox is compatible and then have the drive shaft altered.

[dogoncrazy]

Re: Knocking 1275

Hope you remembered that No 1 pillar has oil feed to rocker shaftwhen you fitted spacers under pillars-easily forgotten!!

[artrider50]

Re: Knocking 1275

Yes, as all the pillars had oil holes I put holes in all of the spacers "just in case"

[artrider50]

Re: Knocking 1275

Yes, as all the pillars had oil holes I put holes in all of the spacers "just in case"

[artrider50]

Re: Knocking 1275

Yes, as all the pillars had oil holes I put holes in all of the spacers "just in case"

[FranklinLeicester]

Re: Knocking 1275

See Misc. section for details of SEMS

[artrider50]

Re: Knocking 1275

Yes, as all the pillars had oil holes I put holes in all of the spacers "just in case"