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The MGF Register Forums • Cam timing, help !
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Cam timing, help !

Posted: Mon Jul 26, 2021 9:37 pm
by Toetsje
Hi all !

while reading hours and hours on this forum I finally reached a situation where I need to ask your support :lol:
Making some great progress in restoring this lovely car which has been originally imported from Germany, it's now time to give some tlc to the original engine (1.8 120HP).
According to the many stories it would make a lot of sense to replace the original cams with the 135HP version as it will result in a bit more umpf with reasonable little effort, knowing that the engine is out of the car and in the process of new timing belts etc.

Although having quite some experience with engines in general, it's the first time of measuring the exact valve opening, duration, closing and overlap timings. I have used the following source as guidance: http://mgf.ultimatemg.com/group2/engine ... timing.htm
Just focussing on the inlet for simplicity now.
According to the source the standard 1.8i 120BHP inlet valve should open at 12 degrees before top dead center (BTDC) and close at 52 degrees after top dead center (ATDC). My actual readings are far, way far from this.

Although the engine was running fine when it was removed from the car, I first started to confirm the current timing. This seems to be fully correct to me. The notch at the front of the crankshaft pulley aligns perfectly with the mark on the plastic shroud.
At the same time, both inlet and exhaust cam are on the marks where they should be:
IMG_20210726_191132702.jpg
IMG_20210726_191113514.jpg
Then I have defined TDC by using a dial indicator on cilinder #1, the moment the needle changes from direction is the moment where the piston changes from direction too. During a small period the dial indicator stays steady while you are rotating the crankshaft, this has been averaged by using the 2 moments where the needle starts moving.
Then, TDC has been marked on the protractor fixed on the crankshaft pulley. This is the reference for all measurements:
IMG_20210726_191231004.jpg
Then I have tried to determine when the inlet valve opens and closes in relation to the absolute crankshaft position. I understand that the crankshaft rotates 2x the speed of a camshaft and therefore the readings should be divided by 2.

First measurement, tried to find the moment when the inlet valve starts to open ever to slightly. Then the same procedure was applied to find the moment when the valve was fully closed (needle of the dial indicator becomes steady while rotating the crankshaft).
This resulted in the following 2 readings:

Opening at 34 degrees BTDC
Closing at 258 degrees ATDC

Dividing these values by 2 gives:
Open @ 17 BTDC vs 12 BTDC according the source
Close @ 129 ATDC vs 52 ATDC according the source

Since it is difficult to find the moment where the valve starts or stops moving I have repeated the measurements but noted the values at 1mm valve change.
This again gives total wrong values, related to absolute position on crankshaft from TDC:

Opening at 10 degrees ATDC (1mm valve lift)
Closing at 220 degrees ATDC (1mm from fully closed)

This is not even close and can't get my head around these readings, what am I doing wrong?


IMG_20210726_191328540.jpg
IMG_20210726_191351115.jpg

Re: Cam timing, help !

Posted: Tue Jul 27, 2021 10:39 pm
by talkingcars
Hi and welcome to the forum

Sorry but I don't know anything about building engines.

James

Re: Cam timing, help !

Posted: Fri Jul 30, 2021 3:56 pm
by Toetsje
Thanks !

Anyone else maybe?

Re: Cam timing, help !

Posted: Wed Aug 04, 2021 10:27 am
by Fraser
I don't know if this is poissible with the K-Series engines, but could you have transposed the camshafts ?

Re: Cam timing, help !

Posted: Thu Aug 05, 2021 3:55 pm
by billdodds
the cam shafts are the same for inlet and exhaust

Re: Cam timing, help !

Posted: Thu Aug 05, 2021 4:20 pm
by Chris Tideswell
I don't know if this is of any help or even relevance to your problem https://youtu.be/HJ__eNHwtww

Re: Cam timing, help !

Posted: Fri Aug 13, 2021 3:28 am
by RobboMC
Hi,
First I'll start with the usual disclaimer that my advice is given as a DIY non-professional and without any warranty at all:

however, the pic you show has the word Exhaust and Inlet facing the locking block incorrectly, so both cams are 180 deg out!

If you have lined up the crank pulley at the service position with the cams like like this then it is all 180 deg out.
Happily it must turn b y hand OK without fouling anything.

When engine is at the service position on the crank pulley, the words INLET and EXHAUST must line up on the pulleys,
with INLET on the inlet pulley and EXHAUST on the exhaust pulley.

DON'T FIRE THE ENGINE UP UNTIL IT TURNS A DOZEN TIMES BY HAND,

If this doesn't make sense to you then please repost at will,
I have some pics somewhere and will look for them on weekend.

Re: Cam timing, help !

Posted: Mon Aug 16, 2021 8:03 am
by Toetsje
You are bloody well right!
Even after checking the things multiple times over it wasn't noticed. Sometimes some new and fresh views are needed to catch these mistakes :)

We'll reset the cams after returning from holidays and measure again.

Thanks all for the great support!