Date: Mon, 20 Jul 1998 13:27:33 +0100 (WET DST)
From: Mark Norman
Subject: Advice please!
Hi everyone, could I ask you for some advice please? Sorry to clog up this mailing service with this sort of question, but we are going to be setting out for the National Weekend at the start of next week (staying overnight at a few places, not driving slowly!), so time is short & this struck me as a good way of getting lots of responses quickly. My newly built engine is giving me a few things to worry about - at this stage I'm not too interested in fine tuning, just in getting to Scotland from Kent without blowing up!
The engine has just completed 500 miles, it is a 998cc with Wills Rings, its head is the type with an oil drain pipe. It has a sports cam, a 24mm Solex carb. and a Lucas 25D distributor - maybe not the best of distributors, but it ought to be OK. It is doing three things which worry me:
1. It pinks if I accelerate medium hard. At present I accelerate softly and back off if it does start pinking, which if frustrating! Have checked the timing: it is fine on tickover (3 deg adv), but at 30,000rpm goes to about 40 degrees advance - this is way too much isn't it? I'll be replacing the distributor when I can afford the time/money to. The main reason I mention this is because it probably bears on the other problems:
2. If the engine pinks, it smokes like crazy. It is also generally more smoky than my previous little 875cc, but I believe this sort of engine is because of the lack of valve oil seals with the sports cam, also I'm told that being a new engine it may be smoky to begin with. My friend who built the engine and I disagree about what the cause of the smoke is - he thinks it is unburned fuel, I reckon it's oil. When it does do this the oil level goes down noticeably, that said, it seems to use a lot of fuel too! Of course a properly tuned engine shouldn't pink, so I hope this problem will go away once a new distributor is fitted.
3. There is a regular and fast tapping/clunking from the top of the engine. It seems to be getting worse with time - you can now hear it while sitting inside the car. It seems to get worse as the engine heats up, but is not noticeable at higher rev's. It is most noticeable when the engine is ticking over. We have taken the cam cover off and checked the top of the engine - can't see anything wrong though. The cam looks fine - it is solidly mounted and shows no abnormal wear, the cam mountings are fine, the chain seems fine, the valve clearances are fine. When we took the cam out, nothing popped out, though we didn't look under the buckets or at the shims. Just sometimes when starting the engine from cold, it initially sounds like it is only running on 3 cylinders - don't know if that is relevant. This is the one I'm most concerned about - help!
I realize it's pretty impossible to tell what's wrong with an engine by e-mail, but I thought there might be a chance that these are symptoms of a common problem with Imps, and someone would be able to say "Oh yes, it's that old problem...". Thanks in advance for your comments anyway,
Mark.
Date: Mon, 20 Jul 1998 23:03:22 +0100 (WET DST)
From: Nickcleak@aol.com
Subject: Re: Advice please!
> 1. It pinks if I accelerate medium hard. [...] Have checked.
> the timing: it is fine on tickover (3 deg adv), but at 30,000rpm goes to
> about 40 degrees advance -
at 30,000 rpm you would probably need 90° advance !
>this is way too much isn't it?
i assume you mean 3000 rev/min .. well no it's not .. did you take off the vacuum advance pipe?
it should be about 20° advance at 3000 rev/min with vacuum pipe off .. or about 36° advance with it on for the normal distributor ...
> 2. If the engine pinks, it smokes like crazy.
Yes , the oil is the cause of the pinking ! you get a puf of smoke and it pinks at the same time as you put your foot down , then it stops pinking when the smoke clears?
> I disagree about what the cause of the
> smoke is - he thinks it is unburned fuel, I reckon it's oil.
excess fuel is Black smoke , oil is Blue or white smoke ....
> it seems to use a
> lot of fuel too! Of course a properly tuned engine shouldn't pink, so I
> hope this problem will go away once a new distributor is fitted.
I would guess the valve guides are worn , have you had it apart and checked ? there should be very minimal play, even certain new guides can be too sloppy ..
what state are the pistons and bores ? if the smoke is there all the time when accellerating hard it may be piston - Bore wear ...
I am running a 930 at the moment with proper valve stem seals and it uses no oil at all , this is a first in my long Imp motoring experience ! No smoke , no oil !
> 3. There is a regular and fast tapping/clunking from the top of the engine. [...]
> The cam looks fine - it is
> solidly mounted and shows no abnormal wear, the cam mountings are fine, the
> chain seems fine, the valve clearances are fine.
> [...] it initially sounds like it is only running on 3 cylinders
The running on 3 cyls may be oil fouling a plug ,
you will probably find the cam followers worn and tipping causing a tapping , also the cam followers may be hitting the top valve spring seats , it is important that they don't as rapid wear of the collet will occur ..
Hope you find an answer ,
nick ....
Date: Tue, 21 Jul 1998 01:37:38 +0100 (WET DST)
From: Gary Henderson
Subject: Re: Advice please!
Hi Mark
30,000 rpm is way too much for running in! ;-))
Is your 25D distributor one intended for an Imp at all? These units were used on a huge range of cars, most of which needed much more advance than Imps do. F'instance, a Minx/Hunter one would be grossly unsuitable although it probably would fit OK. In general. lower compression ratio + slower flame propagation = more advance required.
Don't knock the 25D - they don't get baggy bearings like brands X, Y & Z; also the connection to the breaker-arm doesn't go mysteriously open-circuit like the 45D. The smaller electrical clearances inside the cap demand that it be kept clean to avoid tracking, but there are very few other problems.
Make sure the Delivery Number marking (I think a 5-digit number in the 40000s) is at least one relating to Imps; preferably the proper one for a 998. (The Rootes workshop manual has tables of these.)
Good luck
GaryH
Date: Wed, 22 Jul 1998 10:59:13 +0100 (WET DST)
From: Mark Norman
Subject: RE: Advice Please!
Thanks very much for your comments. yes, 30,000 was a slip of the fingers/brain :-).
>I would guess the valve guides are worn , have you had it apart and checked ?
>there should be very minimal play ,, even certain new guides can be too sloppy.
>what state are the pistons and bores ?
The engine is newly machined, so the pistons, bores & valve guides _ought_ to be OK.
>you will probably find the cam followers worn and tipping causing a tapping , also the cam followers may be
>hitting the top valve spring seats , it is
>important that they don't as rapid wear of the collet will occur ..
I'm going to check out the cam followers then!
>Is your 25D distributor one intended for an Imp at all?
The distributor is off the old 875 engine, hence my surprise at all the knocking, because I wouldn't think the spec would be that far out at all.
I have now removed the vacuum advance pipe (& plugged the hole it left in the carb) & the engine runs a lot better, seems a bit spluttery, but that must be better than knocking (I hope!). I don't now have time to get a different one before we set out, so will just experiment with retarding it some more.
>Make sure the Delivery Number marking is at least one relating to
>Imps; preferably the proper one for a 998.
Is there much difference in behaviour between distributors for a 998 & an 875 then?
Mark.
Date: Wed, 22 Jul 1998 12:27:21 +0100 (WET DST)
From: Gary and Carol Henderson
Subject: RE: Advice Please!
Hi Mark
My Rootes manual doesn't go up to the 998, but the Sport surprises me by having more advance (centrifugal and vacuum) than the HC Mk 2; the LC engine of the van has quite a lot extra again.
The following Distributor Despatch Numbers are quoted:
Mk 1 LC 40968; advance curve ECM.820; Vacuum unit 3-8-7
Mk 1 HC 40905; advance curve ECM.789; Vac 5-11-8
Mk 2 LC 41129; ECM.858; 4-8-5
Mk 2 HC 41122; ECM.857; 4-14-8
Sport 41132; ECM.857; 3-10-9
The 41132 gives 21-25 deg @ 3500 rpm (plus of course the static 3 deg setting); Vac18-22 deg @ 15" Hg
The 41122 gives 17-21 deg and 14-18 deg @ 18" respectively
The 41129 gives 25-29 deg and 8-12 deg @ 11" Hg respectively.
Hope this helps a bit - I would guess that the bigger bores would demand a little more advance as the flame-front has further to travel (and less time to do it!) Your 36 deg @ 3000 rpm sounds too much if it is centrif. only, but reasonable if the Vac is active also with engine unloaded.
These 25Ds were so 'interchangeable' that you might have one that really belongs to something else!
Does anyone have the Despatch No of the real 998 dissie?
Hope this helps
Cheers
GaryH
Date: Thu, 23 Jul 1998 19:49:28 +0100 (WET DST)
From: Nickcleak@aol.com
Subject: Re: Advice Please!
> Is there much difference in behaviour between distributors for a 998 & an
> 875 then?
There isn't a 998 distributor .. most people used the comp distributor which was suited the R 17 but it had no vacuum advance ... so cruising on light throttle was noisier and less economical than it could have been ...
Nick ...
Date: Fri, 24 Jul 1998 15:48:21 +0100 (WET DST)
From: Gary and Carol Henderson
Subject: RE: Advice Please!
Hi Mark
Just a thought re static timing...
I worried about CT475 seeming to require to be about 0.5 deg AFTER TDC, and puzzled over such variation when the distributor-drive is direct from the crankshaft, until I realised that the tin pointer for the timing-mark bears only a haphazard relationship to the contents of the crankcase! It's fixed by the timing-case bolts with two holes & these holes have a generous clearance, hence it can be made to point almost anywhere. It should have been dowelled; then almost all variation in timing between engines would have gone away.
Re bucket-followers: Good detective work! Watch the various height-limits specified in manual, to avoid possibility of shims jumping out of the recess in the spring-retainer.
Cheers
GaryH
Date: Fri, 24 Jul 1998 22:20:10 +0100 (WET DST)
From: Nickcleak@aol.com
Subject: Re: Advice Please!
> Thank you all for your help on my noisy engine and distributor problems.
> We're setting out towards Scotland tomorrow
I wish you a memorable trip ....
> In case anyone is interested, here is what was wrong with the engine,
> causing the tapping noise:
yes , VERY interested thanks ... "you will probably find the cam followers worn and tipping causing a tapping , also the cam followers may be hitting the top valve spring seats , it is important that they don't as rapid wear of the collet will occur .."
I thought that was the problem !!
The collets are the main problem i think , they do seem to vary ..
the top face can be ground down to a minimum distance between the top and the underside edge of the spring seat shoulder of 0.292 in ....
The thickness of the Cam follower should be 0.203 to 0.207 in
this seems to be fairly accurate on the ones i have measured
NOTE : The cam followers from the sunbeam 930 are thicker ..!!
> The timing seems a lot better too - [...] I don't know how good a thing
> this is, but it has stopped the knocking, and the engine sounds & feels a
> lot better to me, which I reckon is the most important thing!
yes all imp engines are individuals !
Nick ...
Date: Sat, 25 Jul 1998 09:04:21 +0100 (WET DST)
From: Simon Trickett
Subject: RE: Advice Please!
I hope when you say collect you mean spring cap, as the collets (2 per valve stem) should never be able to touch the tappet due to the shim !
Good detective work anyhow!
Simon Trickett