8 replies to this topic

[euaniebabs]

So, my well loved Minispeed Concept 37 1380 is getting a little tired I guess. I bought it in around 2008. Around 10k miles and after putting back into the car after a year of body improvements, is more smokey then I remember. Still goes like a scalded cat, I believe CR was in the region of 12,5:1 along with lightened assemblies, Omega pistons, 45DCOE, piper 276, straight through exhaust to a single rear box and 1.5 roller rockers.

At first I put it down to not running for a year. It had a fresh cometic headgasket and general decoke. Value guides seemed fairly tight still and I fitted new stem seals. Inside the rear tailpipe gets wet with oil as well as getting black oil spots on the boot lid.

100 miles on and there is clearly an issue. Seem to be getting a fair amount of blow by and oily exhaust. Not on over run, but on idle and under load. Compression good at 210psi +/- 5 across all four. Leak down test reads moderate across all four with no valve leakage, instead can be heard in the crankcase. Have opened up breather restrictions, but have now removed the engine to measure bores properly. There is some light vertical witness that can be seen through the honing marks as pictured by my basic boroscope.

Head coming off shortly but in the mean time, 5 ports and 2 bores pictured. Evidently it runs quite rich and always has, but has not really been properly retuned or given a long hot run since refitting. Exhaust port nearest the rad seems wettest with oil.

Am guessing best case rings and a hone, worst case liners, or new block.

Any thoughts, words of wisdom or similar?

I had originally hoped for a simple head fix of guides, but given the amount of oil, I fear the worst!

Euan

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[sledgehammer]

I would have poured some red-ex down the bores to see if the rings are a bit gummed up / sticking , then give it a blast

 

but as you have the engine out have a good look at the rings

 

something to have a good look at is the oil return holes at the back of the oil control rings

on some pistons they do gum up , but can look clear at first sight , so check with a small drill
 

as you probably know worn piston ring gaps can pump oil up as well

 

also valve stem seals can seem tight , but can have ridges in them allowing oil past

breathers can seem clear , but could still let oil past into the intake with the fumes - although your ports seem clean - I would expect a lot of carbon / oil there

 

when a breather gums up on the wire wool material , it won't scrub the oil out of the vented fumes , but will still sometimes allow flow - if that makes sense 

 

the bores look quite scored - but I know a camera can exaggerate this , some blocks can be relined , but not all IIRC
 

hope it's not scrap - best of luck

Edited by sledgehammer, 11 September 2018 - 08:24 PM.

[Bat]

Hi,

Are those scuffs inline with the gudgeon pin?

Cheers 

[mini13]

I don't like the look of those vertical scores...

[cal844]

Check the gudgeon pins aren't walking out, that's what it looks like.

It's either that or if your very lucky just gummed rings

[Dusky]

Chances are slim the pins are walking out.
But your decoke has a high potential of putting grit between the ring and bore.

[GreaseMonkey]

Firstly I'd be giving all the breathers a good clean out and then replacing the valve stem oil seals with a good well known brand. Chances are I think, over the years the stem seals may have hardened?

[Spider]

You might get away with a Hone and new rings.

 

Otherwise, a decent machine shop should be able to fit sleeves and go again from there.

[mini13]

if you end up sleevig it, you'll be looking at new pistons too, as the max overbore on sleeves is about +40