MB still playing up

[MYT801]

My MB has had
new plugs and leads
new coil
rebuilt dizzy
new inlet manifold
rebuilt carby and tuned

still farting about i have also done a compresstion test and they returned

piston 1 = 149
piston 2 = 160
piston 3 = 152

Rebuilt about 1000kms ago.. if anyone has any ideas, can you let me know?

[Tez]

http://www.teammightyboy.com/forum/view ... une#p47281

[bswift16]

hey there

what is exactly wrong with it ???/
check your cam belt tightness, i have just replaced mine after spending a month (and a small fortune) on fixing everything else. if the tensioner is not working properly, or the belt is stretched it will run real rough and splutter, and feel like it wants to stall especially when backing off the revs

this may help it may not

[MYT801]

well its a new belt and tensioner ...

[Brayden]

still farting about i have also done a compresstion test and they returned

piston 1 = 149
piston 2 = 160
piston 3 = 152

Rebuilt about 1000kms ago.. if anyone has any ideas, can you let me know?

I've got bad news for you. 145 is the service limit for these engines. A fresh motor should have close to 200PSI across the cylinders.

I'll take a guess and say that you have sticky valves.

[Husky]

As Brayden said The compression is lowish, But still within service limits. My F8b has similar compression and doesn't miss a beat.
I'd be interested to know what other guys MB's compression are? I think even with a good reconditioned motor you would harded pressed to get more than 180psi... IMO
How do sticking valves get fixed?

[Brayden]

Sticky valves are mostly caused by over-tight rocker adjustment, so the valves don't seat properly and you loose compression.

If a rebuilt motor isn't testing at 190+ then it hasn't been built right IMO!

[Husky]

Brayden,
I stand corrected , I thought the manual stated around 180psi-190 for a "new" motor? Thanks for letting me know. I'll be sure to check when my motor is rebuilt

[MYT801]

i am starting to think about pulling the head off it can get it fully reco-ed (my father just pulled the head off a car that ran with no oil) ran fine when first started but then it got a load of dirt and crap in the fuel through it drove up through buladelah in a traffic jam then it started to miss and do all sorts of stuff. ( i did a real bad thing which drove it upto foster and back while it was doing that)

[Brayden]

Brayden,
I stand corrected , I thought the manual stated around 180psi-190 for a "new" motor? Thanks for letting me know. I'll be sure to check when my motor is rebuilt

The manual says 192psi new with a service limit of 140psi.

[MYT801]

should i i take the head off and reco it?

[Brayden]

I'd do a leakdown test first to work out why the compression is so low, but if the head was installed without being rebuilt then who knows what condition it is in.

[Husky]

warm the engine up to do a compression check, Take out the plugs put a cap full of oil down each cylinder 1 at a time. If the compression rises its a fair bet the rings are worn(the oil helps seal between the ring and the cylinder), if the compression doesnt change you may have valves not seating properly(leaky). Then you know your problems in the head.
Even with lowish compression however from worn rings it wont cause the problems you describe.

[MYT801]

thanks mate, ill try that tomorrow after i get home from school.

[eris]

When you say the M/B is still "farting about" can you be more specific. is it running rough at idle? under load? at high revs? stall at high revs? missing as you accelerate? back fireing through carbi/exhaust.... ????