MGB rocker cover pressure

MGB rocker cover pressure

Author
Discussion

shaunmorris

Original Poster:

66 posts

227 months

Thursday 28th August 2014
quotequote all
Hi,
About a month ago I bought a standard 1978 MGB, I have noticed that it uses a lot of oil and blows smoke under heavy acceleration but not when cruising at steady speeds. I should mention the engine was rebuilt about 500 miles ago and produces 94bhp on a rolling road. This evening I noticed that if I remove the oil filler cap with the engine running the tick over increased and the engine runs much smoother and if you place your hand on the filler you can feel the engine sucking your hand to the rocker cover. At this point I started to rev the engine and notice that without the cap the engine was not smoking when revved. Replace the cap and the tick over drops engine runs rough and starts to smoke when revved. question is does this point to worn valve guides ? is the engine sucking oil into the cylinders due to the increased negative pressure with the oil filler cap in place ?

Any thoughts or advise ?

Many Thanks

shaunmorris

Original Poster:

66 posts

227 months

Thursday 28th August 2014
quotequote all
just realised although I said the car was standard, the previous owner fitted one of those polished rocker covers with a vented cap. vent is very small could this be the problem.

Thanks

nta16

7,898 posts

233 months

Friday 29th August 2014
quotequote all
possibly - change the oil filler cap to the black plastic filtered and vented £4 from MGOC Spares £11 from some other suppliers for the same cap - MGOC Spares - Oil filler cap (vented) - Black GFE6003

lesson one bling's usually for show not go!

also check that the breather hoses aren't blocked or collapsed but it doesn't sound like they would be, there's a John Twist video telling you how to check this

you need to put more miles on the engine and do an oil and filter change to whatever are the engine builder's requirements

if you've got a bright red painted MGB, especially if it has chrome wire wheels, then you might need to check a lot on it as they're usually for show rather than go

anyway, should you really be driving a MGB this late in the year, no wonder you have problems!

soon be SORN time

ETA: check any plates or seals that the breather pipe comes from for security and sealing

Edited by nta16 on Friday 29th August 09:41

shaunmorris

Original Poster:

66 posts

227 months

Friday 29th August 2014
quotequote all
Thanks, sounds like a plan, I have ordered a cap, I will let you know how I go on.

Many Thanks

xyyman

1,075 posts

224 months

Saturday 30th August 2014
quotequote all
Had a similar issue on my 'C' earlier in the year. Coincidentally it also has a fancy alloy rocker cover and cap. On investigation it was found that the crankcase breather had been cobbled up and was not releasing pressure fully. My solution was to vent to catch tank and filter. All's well now. Good luck and enjoy it.

woodytype S

691 posts

236 months

Tuesday 2nd September 2014
quotequote all


if you've got a bright red painted MGB, especially if it has chrome wire wheels, then you might need to check a lot on it as they're usually for show rather than go

anyway, should you really be driving a MGB this late in the year, no wonder you have problems!

soon be SORN time

ETA: check any plates or seals that the breather pipe comes from for security and sealing

Edited by nta16 on Friday 29th August 09:41

[/quote]
very funny ha ha

nta16

7,898 posts

233 months

Tuesday 2nd September 2014
quotequote all
woodytype S said:
nta16 said:
if you've got a bright red painted MGB, especially if it has chrome wire wheels, then you might need to check a lot on it as they're usually for show rather than go

anyway, should you really be driving a MGB this late in the year, no wonder you have problems!

soon be SORN time

ETA: check any plates or seals that the breather pipe comes from for security and sealing
very funny ha ha
yes and far too often accurate

Dbest92

300 posts

132 months

Tuesday 2nd September 2014
quotequote all
woodytype S said:
if you've got a bright red painted MGB, especially if it has chrome wire wheels, then you might need to check a lot on it as they're usually for show rather than go

anyway, should you really be driving a MGB this late in the year, no wonder you have problems!

soon be SORN time

ETA: check any plates or seals that the breather pipe comes from for security and sealing

Edited by nta16 on Friday 29th August 09:41
very funny ha ha
Now I won't have that wink my shiny red mgb with chrome wire wheels is used often all year round smile. Although there sadly is truth to what you say. I rarely see classics on the road even in summer, yet go to a local show and you see loads which turn out to be be owned by someone just down the road, yet never seen on the road!

shaunmorris

Original Poster:

66 posts

227 months

Tuesday 2nd September 2014
quotequote all
nta16, you got it spot on, put a new original filler cap on the car, went for 45 minute drive and no smoke !
PS my B is shiny red and you will see it on the road all year round.

Thanks

nta16

7,898 posts

233 months

Tuesday 2nd September 2014
quotequote all
Shaun,
glad to help, and thanks for reporting back

most owners won't believe that a plastic part can be as good as a shiny bling part or make such a difference but I was told it many years ago

that plastic part could last you decades, if towards the time the engine starts to need another rebuild you can even clean the plastic cap - or buy another


Edited by nta16 on Tuesday 2nd September 21:34

nta16

7,898 posts

233 months

Tuesday 2nd September 2014
quotequote all
Darren,
look and learn, you won't believe me but you might Shaun

Expatloon

215 posts

156 months

Saturday 13th September 2014
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FWIW I've had an alloy cover and chrome cap on my engine for 25+ years and experienced no breathing problems whatsoever, also fitted them to several others.

Check the tappet side cover breather by blowing down it, it should offer little or no resistance.

nta16

7,898 posts

233 months

Saturday 13th September 2014
quotequote all
some bling caps might be better than others but the black plastic filtered and vented oil filler cap seems the best to fit most often

checking covers and pipes was suggested

OP changed to the black plastic filtered and vented oil filler cap and felt that this resolved the problem, in this case black plastic filtered and vented oil filler cap 1, bling cap 0