[Healeys] Sprite question for my neighbor

Sun Nov 16 17:12:39 MST 2025

Hi Steve,

Having read your update and seeing that you have eliminated the cylinder
head as the source of the issue, I wanted to take another shot at the
problem.

The recent compression test results may be shedding light on the issue.
Based on your readings, the ratio of the lowest to the highest compression
is 75% when cold (120/160) and 79% when hot (130/165). While not an
absolute rule, a general rule of thumb for a smoothly running engine is a
ratio of 90% or greater. A freshly rebuilt engine showing 75% is not a good
sign. Could you try adding a small amount of oil to the third cylinder and
retesting the compression?

If poor piston ring sealing is causing excessive blow-by, this increased
pressure in the bottom of the engine could overwhelm the crankcase
ventilation system.

Though I'm not an expert on the BMC A-series engine, I recall the crankcase
breather usually attaches to the tappet cover on the side of the engine. It
sounds like the current breather setup on your neighbor's engine—located
where the old fuel pump attached—might be too low and too close to the oil
in the sump. Does this engine have a breather on the tappet cover, and does
air pass through it easily?

Good luck with the continued investigation.

Regards,
Harold

On Sun, Nov 16, 2025 at 1:14 PM Michael Salter <michael.salter at gmail.com>
wrote:

> In my experience Steven, that's not how it works with piston rings.
> Rings are specific to a particular bore size. If the bore is say 0.010"
> oversize then 0.010" oversize rings are what must be fitted.
> Installing an oversize of ring without accurately measuring the bore and
> checking that the pistons and rings are correct for  that bore just won't
> work.
>
> M
>
>
> ------------------------------
> *From:* Steven Kingsbury <airtightproductions at me.com>
> *Sent:* Sunday, November 16, 2025 2:24:30 PM
> *To:* Harold Manifold <manifold at telus.net>
> *Cc:* Michael Salter <michael.salter at gmail.com>; Healey Mail List <
> healeys at autox.team.net>
> *Subject:* Re: [Healeys] Sprite question for my neighbor
>
>
> The engine was a fresh rebuild when bought. The car was sold because of
> the excessive oil blowing out after the fresh rebuild. The head was taken
> off and examined at a local machine shop and passed with flying colors. The
> pistons and rings were also taken to the shop where the machinist remarked
> that the rings might have been too small and suggested 10 over rings. New
> rings went on, everything put back into the engine and again, it runs
> great, just blows the oil all over the place!
> Michael, compression test today after a bit over 100 miles with the new
> rings: 160, 148, 120, 130. Saw some suggestions on an MG forum for fixing
> crankcase ventilation. Will see what my neighbor decides to do and will
> update later. Thanks all for the words.
> And just now, after driving the car another forty miles or so, the
> compression now sits at: 165, 155, 130, 150. So that's getting better. Will
> definitely take a closer look at the rocker shaft and bushings. Again,
> thanks to all for the possible foibles facing this engine.
> Steven
>
> On Nov 16, 2025, at 8:52 AM, Harold Manifold <manifold at telus.net> wrote:
>
>
> Hi Steve,
>
> The issue you described with your neighbor's 1275 engine may be related to
> a similar problem I've encountered.
>
> I know of a recently rebuilt engine that experienced comparable excessive
> oil blow-by. The cause, in that case, was a poorly refurbished and refitted
> rocker shaft and bushings. Without adequate restriction between the rocker
> shaft and the bushings to regulate the oil flow, it resulted in an
> excessive amount of oil being pumped to the top of the engine.
>
> I hope this provides another avenue for investigation.
>
> Regards,
> Harold
>
> On Sat, Nov 15, 2025 at 1:12 PM Michael Salter <michael.salter at gmail.com>
> wrote:
>
> Hi Steve, what you describe sounds to me like excessive blow-by.
> I would recommend a compression test before going too much further.
>
> M
>
>
> ------------------------------
>
> *From:* Healeys <healeys-bounces at autox.team.net> on behalf of Steven
> Kingsbury via Healeys <healeys at autox.team.net>
> *Sent:* Saturday, November 15, 2025 3:33:19 PM
> *To:* Healey Mail List <healeys at autox.team.net>
> *Subject:* [Healeys] Sprite question for my neighbor
>
> My neighbor bought a bugeye that had a 1275 engine put in it. It runs
> well, but blows oil like crazy out of the oil cap on the valve cover. It
> does not have a timing cover ventilation valve, but a fitting was made to
> fit onto where the old fuel pump fit on the side of the crankcase/block.
> When he hooked the hose from that fitting to the carbs, oil was no longer
> being blown out, but oil was then being sucked into the carbs and he was
> burning oil like crazy.
>
> It seems the pressure in the crankcase is so great it is pushing oil up
> the push rods into the rocker assembly, out the filler cap and all over the
> engine. I'm not familiar with the 1275 and have no ideas on how to vent the
> pressure in the crankcase. Can anyone of you guys point me to a possible
> solution? Thanks in advance for the advice.
> Steven Kingsbury
> BN1
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