Jump to content

Engine Rattle/Knock


Recommended Posts

Although I am a long term wet liner owner, having bought my first TR3A in January 1963, and have been a Register member since 1984 for some odd reason I have never given the forum more than the occasional glance.

However, since starting this topic just a couple of days ago I have been pleased and impressed with the volume and quality of the response it has had.

Unfortunately, so far it has not so far pin pointed the source of the noise but #8 and #9 have been particularly helpful. The best description of the noise is in #8 'ball bearings' pinging around inside the manifold. Although I didn't say so in my original post (I should have) I had imagined it as being like tapping the thin steel rocker or timing chain cover with a small hammer at half engine speed. I had convinced myself that the noise was mechanical, generated by metal hitting metal, hence the long process of strip downs and replacements over the years. I should add that I have only ever replaced worn or damaged parts, so have not been totally wasting my money.

I briefly mentioned that an acoustic instrument had indicated that the noise was coming from the vicinity of the exhaust manifold. At the time I was so convinced that the noise was mechanical, and there are no moving parts in this area I had discounted what the high grade Brüel & Kjær instrument was telling me, partly because neither my TR3 owning friend who had borrowed the instrument or I were familiar with using it.

After reading #8 & 9 my confidence in the scientific approach has been reinstated and I believe the exhaust manifold is the culprit. It was purchased from Moss and fitted in about 1986 to replace the standard cast manifold that was cracked and leaking. It is fabricated from Mild rather than Stainless steel and when removed last week for inspection it seems to still be in perfect condition. Although I didn’t do a pressure test I am sure there are no cracks, holes or corrosion, not a hint of soot to be seen. Remembering that there is no noise for about a minute when starting from cold, only the exhaust pipe temperature has changed in this short time. Water, oil and the body of the engine have not had time to heat up significantly. Remembering also that the noise ceases at just over 1000rpm.

I mentioned earlier that the car is fitted with 123 programmable ignition. The curve I use increases from static advance by 10 degrees @ 1000rpm.

I believe the noise is set up by a resonance that is set up as the manifold expands at the present static advance setting. Noise stops as engine speed and/or advance setting increases.

In the short term I have set idle speed just over 1000rpm. I am reluctant to change the ignition curve as the engine starts and performs well as it is.

I would like to hear comments, positive or negative on my conclusions.

In order to restore normal idle speed I am considering altering the manifold vibration characteristics by using exhaust clamps on each of the four downpipes and then bolting a steel strap from clamp to clamp. All four, 1 and 4 and 2 and 3 or some other combination? What little I knew of these vibration characteristics 60 years ago I have long since forgotten. What do you think?

Link to post
Share on other sites

I have a Phoenix stainless 4 branch manifold on my '3. a short while after fitting I noticed that a t certian revs there was a resonance which turned out to be two of the downpipes being just a bit too close together, & they were touching at the resonant revs, & making a strange noise. I would not say it was a knocking noise though, bore a sort of "singing".

 

The cure was to (carefully) hammer a scrap piece of sheet metal between the pipes to push them slightly further apart. (then remove the metal)

 

Bob.

Link to post
Share on other sites

Dick,

Glad you found my response of some help in deciding the probable cause of your noise. I put it down to expansion of the metal in the manifold/header but it really sounds like something is loose inside. I also had several fiddles with the tickover which may have had an effect in reducing my noise. I think I am around 900 rpm at present which is a tad fast but relatively smooth as I belive my car was fitted with a 4a cam.

Sorry that I cannot provide a tape of the noise as I did not get around to starting her up today having spent the morning putting new 400lb front springs in my, ahem, cough, midget.

Hope to get her running later this week after the snow/salt has gone and will let you know if there is any noise.

I guess that there are enough folk on here with enough different cars and many years of experience for someone to have come across most problems,however strange....wisdom of the crowds.

John

Link to post
Share on other sites

Dick,

Finally got around to firing up the TR today. It has sat for too long but this afternoon was beautiful after this mornings snow had gone. It coughed and spluttered a bit whilst getting it running and so did not detect any of the strange tinkling noises--hopefully they may have gone altogether.

I had really been looking forward to taking it for a run. Once filled with air (two tyres a bit flat) fresh juice and overcoming mild confusion between the choke and air direction vent (been driving a car from the 'other side' recently) I had a great time.

Attached pic of me getting my kicks on the A66, they really are all the better for being driven.

John Spost-14529-0-60701400-1522966415_thumb.jpg

Link to post
Share on other sites

Looking good.

Its great to get them out and used.

 

I blew (drowned) the cobwebs away at castle Combe in my 3a

 

Wonderful fun.

H

Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Restore formatting

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
×
×
  • Create New...

Important Information

Please familiarise yourself with our Terms and Conditions. By using this site, you agree to the following: Terms of Use.