Lotus Elan

low compression

PostPost by: Craven » Mon May 15, 2017 7:30 pm

Hi Dave,
Your thinking is OK, I would look at the cam sprocket alignment marks at TDC as per manual, they will probably show the Exhaust sprocket is one tooth out, unlikely this is deliberate but possible.
Unfortunately you need to use a timing disk etc if you want to do a full check on cam timing, max lift and so on, this can give you a headache unless done carefully and methodically. I use the rotation of the cam follower bucket to find zero clearance point and as you have realised tappet clearance is an important factor and is often overlooked.
Back to your low compression readings, going through the post from other contributors they have covered the checks that can think of.
Ron.
Craven
Fourth Gear
Fourth Gear
 
Posts: 905
Joined: 14 Sep 2013
Location: south coast uk

PostPost by: daverubberduck » Mon May 15, 2017 9:23 pm

Many thanks for your input Ron, much appreciated. The alignment marks look pretty good. Maybe the exhaust cam is slightly out in the right direction i.e. clockwise in the pics, but moving it back by one tooth would worsen the alignment. Before dong a full timing check, I think I will put the car on a rolling road to see how the performance of the engine compares. If it looks OK then it's not worth pursuing and better left alone.
Dave
Attachments
timing-marks-2.jpg and
timing-marks.jpg and
daverubberduck
Second Gear
Second Gear
 
Posts: 165
Joined: 03 Aug 2009
Location: Essex, UK

PostPost by: promotor » Tue May 16, 2017 7:51 am

Regarding the sprocket timing marks : if you have a standard type sprocket (ie an inlet one) fitted to the exhaust cam you will be one tooth out - inlet and exhaust sprockets are marked differently ie there is one tooth difference where this mark occurs.
If you have an exhaust one on the inlet and vice versa that cold be even more interesting!
promotor
Fourth Gear
Fourth Gear
 
Posts: 507
Joined: 16 Mar 2012
Location: Derbyshire, U.K.

PostPost by: daverubberduck » Tue May 16, 2017 1:03 pm

Checked the sprockets for marks, picture below says everything. I'm pretty annoyed, this engine was recently stripped and put back together by a well known company who should know better. Question now is - how big a job is it to swap the cams. Can it be done without removing the front cover?

Thanks again for everybody's help. This site is such a godsend.
Dave
Attachments
inlet-cam-sprocket.jpg and
daverubberduck
Second Gear
Second Gear
 
Posts: 165
Joined: 03 Aug 2009
Location: Essex, UK

PostPost by: promotor » Tue May 16, 2017 1:11 pm

Don't swap the cams - just swap the sprockets! Makes the job much easier (unless there is reason to suspect that the cams are wrong also, but then again how can you 2nd guess someone who is un-2nd-guess-able?)! Still a fiddly job getting the marks in the correct place as the crank and cams will all want to turn while you do it! And it is important to not stray away from TDC as you will risk valves hitting each other and/or the pistons

But before you put the sprockets back on double check the timing marks against each other with one laid on top of the other. The exhaust mark is one tooth further round in a clockwise direction when compare with the inlet mark.
promotor
Fourth Gear
Fourth Gear
 
Posts: 507
Joined: 16 Mar 2012
Location: Derbyshire, U.K.

PostPost by: daverubberduck » Tue May 16, 2017 2:10 pm

I guess I need to make sure that it is only the sprockets, not the cams. Would the car run at all if the cams were wrong way round?

I have looked for markings on the cam shafts and have found:
Inlet camshaft : MC23929 , A , B26E351
Exhaust camshaft : MC23929 , C , B26E351

Now this seems opposite way round to this thread:
lotus-twincam-f39/camshaft-identification-t16829.html

So maybe the cams are wrong too. I need to make sure about this. Will search books and on-line, or maybe someone here can tell me. The cams are C type (single groove).
Dave
daverubberduck
Second Gear
Second Gear
 
Posts: 165
Joined: 03 Aug 2009
Location: Essex, UK

PostPost by: daverubberduck » Tue May 16, 2017 2:44 pm

Surely the cams are the same, aren't they? I have measured the lift on both and they are the same, and the timing must be the same, so no need to swap cams... or am I wrong?
daverubberduck
Second Gear
Second Gear
 
Posts: 165
Joined: 03 Aug 2009
Location: Essex, UK

PostPost by: Craven » Tue May 16, 2017 2:50 pm

Hi Dave,
OK so you have decided to open the can of worms anyway, I did not come back with the other well known possibilities because for an inexperienced Twincam enthusiast all sorts of unintended consequences may follow removing the timing chain, ignition timing gets moved as an example.
I would suggest you firstly establish the current cam timing, find the cam duration for both cams are they the same, 272 deg for sprint 26/66/66/26.
If as you say the engine was rebuilt by a professional there may be a reason you see what you see.
There is enough knowledge on this forum to sort almost any Elan problem and will make sure you don’t fall into usual traps.
Ron.
Craven
Fourth Gear
Fourth Gear
 
Posts: 905
Joined: 14 Sep 2013
Location: south coast uk

PostPost by: daverubberduck » Tue May 16, 2017 3:01 pm

Thanks Ron. Is it possible to remove the sprockets without taking the engine apart?
Dave
daverubberduck
Second Gear
Second Gear
 
Posts: 165
Joined: 03 Aug 2009
Location: Essex, UK

PostPost by: daverubberduck » Tue May 16, 2017 3:13 pm

I think the answer to my last question is yes, I have to remove the half moon shaped plugs and undo the nuts. The tricky bit will be putting it back together. If I align the timing marks on the sprockets, then maybe double check by measuring the opening and closing angles of the valves as I did before. Am I on the right lines?
daverubberduck
Second Gear
Second Gear
 
Posts: 165
Joined: 03 Aug 2009
Location: Essex, UK

PostPost by: promotor » Tue May 16, 2017 4:06 pm

It truly is a can of worms - the best thing to do initially would be to confirm the TDC lines/marks on the sprockets and ignore what is written on them for now. I will get some photos later for you to show the marks on proper inlet and exhaust sprockets so you can compare to yours.
Last edited by promotor on Tue May 16, 2017 4:30 pm, edited 1 time in total.
promotor
Fourth Gear
Fourth Gear
 
Posts: 507
Joined: 16 Mar 2012
Location: Derbyshire, U.K.

PostPost by: alan.barker » Tue May 16, 2017 4:09 pm

Be sure to release timing chain tensioner as far as possible before removing sprockets. If you don't you will not be able to refit sprockets against the tension.
Alan
Alan.b Brittany 1972 elan sprint fhc Lagoon Blue 0460E
alan.barker
Coveted Fifth Gear
Coveted Fifth Gear
 
Posts: 1709
Joined: 06 Dec 2008
Location: BRITTANY FRANCE

PostPost by: daverubberduck » Tue May 16, 2017 4:37 pm

Thanks Alan, good point.

I'm undecided about whether to attempt this myself. It seems like something I could do, but then again I'm almost certainly underestimating the difficulty.
daverubberduck
Second Gear
Second Gear
 
Posts: 165
Joined: 03 Aug 2009
Location: Essex, UK

PostPost by: alan.barker » Tue May 16, 2017 5:43 pm

Maybe someone with a Lotus lives near you so they could pop round and look over your shoulder.
If you're not sure don't do it. We don't want you bending some valves do we :roll:
Alan
Alan.b Brittany 1972 elan sprint fhc Lagoon Blue 0460E
alan.barker
Coveted Fifth Gear
Coveted Fifth Gear
 
Posts: 1709
Joined: 06 Dec 2008
Location: BRITTANY FRANCE

PostPost by: daverubberduck » Tue May 16, 2017 5:53 pm

Well I know someone not far away who knows all about engines, maybe I will ask him to do it. It would cost me, but not a lot, certainly not as much as it would if I did it and got it wrong.
daverubberduck
Second Gear
Second Gear
 
Posts: 165
Joined: 03 Aug 2009
Location: Essex, UK
PreviousNext

Total Online:

Users browsing this forum: No registered users and 2 guests