What Causes Poor Power

[calvin streeting]

after doing a lot of work on my engine (cam chain etc), it started back up right away and sounded fine.

I did a compresion test and got:

140,145,140,130,145,150,140,140

This is a M116.895 engine and i cannot find what the compresion should be. but as they are all kind of in the same ball park surley I havent got some seriosly wrong (i hope)..

before i took it of the road, it would run but had now power and wouldn't even climb a small hill.

now i have it back togther it still has no gumph. that means if i put it in gear and put my foot to the floor. it crawls along.

any help??

[Nutz]

Are you sure the cams were lined up properly?

[s class]

CHeck the basics - make sure the cam timing is correct.

Next, I would suspect that the bushes in the throttle linkages have collapsed - check these, and also check the setup of the whole linkage assembly.  Its explained clearly in the library. 

If all that checks out, I'd next start looking at fuel pressures and flow rates. 

[13B]

Check your automatic transmission has enough fluid in it - do a stall test for each gear and confirm its within specs.

My race car has all 8 cylinders within the 140-150PSI range (down from 180PSI due to high milage) so your compression figures should give you a good amount of performance.

I.

[TJ 450]

You should consider the ignition timing. Does it backfire as well?

Tim

[calvin streeting]

cool many thanks lots of things to check..

do a stall test for each gear and confirm its within specs.

whats one of those... ?

You should consider the ignition timing. Does it backfire as well?

yes it dose backfire in the inlet. but only when you rev it hard .. but no backfire out of exhast.

[calvin streeting]

ok photos of cam chain timming







so it looks like i need some offset keys 

I re did the ignition timming and co2 levels.. and now she pulls forward when i put my foot down, still not tarmac pulling, but that might meen i need to do some fine tunning.. (when the rain stops...)

[s class]

If I read those timing marks correctly, the damper is at 6 deg BTDC.  You have advanced the right cam a little bit far, so the true damper reading is probably in the 10 deg BTDC region.  At a guess, the left cam will be timed about 5 deg ATDC. 

I would say that the right hand cam has been advanced by one tooth... if this is corrected, you will see it at about 5 deg ATDC. 

So yes, you will need offset keys to get it spot on.  The left cam needs one, the right cam needs two keys of the same value. 

[calvin streeting]

If I read those timing marks correctly, the damper is at 6 deg BTDC.  You have advanced the right cam a little bit far, so the true damper reading is probably in the 10 deg BTDC region.  At a guess, the left cam will be timed about 5 deg ATDC. 

blimey that makes my head hurt.....

so first i need to check your theory/maths by undoing the chain and rotating the right hand cam anticlockwise by one tooth, and then recheck and take more photos..

ps. should i pre order the 4 and 6.5 keys...

[s class]

4 degrees at the cam is equivalent to 8 degrees at the crank.  I would suspect you will need the 2.5 degrees keys.  Rotate the engine again until the damper is bang on 0 degrees, and see where the marks are.  If the right hand cam's mark has gone past 0 degr already, then yes, the cam is advanced by one tooth.  Next nudge the crank along until the left cam's marks line up.  Then read the crank timing, and that will determine the offset key needed at the left cam.  I suspect you will see about 5 degrees on the crank, meaning that you need a 2.5 degree key on the left cam. 

Shout if you need further explanation. 

[calvin streeting]

ok.. i just need to find a supplier in (or ships to) the UK..

but i am finding that uk suppliers are charging lots for parts ie.. chamshaft gears priced at £220 each....

[calvin streeting]

Blimy Merc Want £6.00 per key...(thats £18 for a set)

I think i might leave england one day... to somewhere warmer.. less rain... and cheaper..

[s class]

Check the timing first accurately.  Having another look now at your photos, I think actually you may find the left cam will be very close to spot-on as it is. 

[calvin streeting]

ok.. but i take it i would still need to either rotate both cams by one tooth
but ??

360   Degrees
36   Teeth
10   Degrees Per Tooth

so that would send the crank forward 20 Degrees and thus put it at the 14 ATDC (20-6) which is worse than before i replace the chain.. 

is it just me or is there something strange here. i checked it by rotating the engine and until the left cam (as per standing in front of car looking at engine) was at the mark. and then took the photos.

[s class]

no no no. 

Left and right is defined as seen from sitting in the car. 

Firstly, Can you confirm that in the picture of the crank damper, it does indicate about 6 deg BTDC (photo not that clear for me).

If this is the case, I think that if you line up the left cam marks, you will find the damper pretty close to "0", in other words no offset keys needed. (Even with offset keys, the best you are realistically likely to get is +/- 3 degrees)

OK so that takes care of the left cam.

Now, onto the right cam.  If you line up the right cam's marks accurately, I think you will find the damper shows about 10 deg BTDC.  My brain (what's left of it anyhow) is churning over the maths.  I'll get back to you. 

This reply is certainly more considered and accurate than my previous ones which were a bit off-the-cuff.

Thanks