Hello again, engine builders. I'm working on getting my 3.8L (9:1 compression) engine back together and I will be ready to install the head in a couple of weeks. I have the standard "Payon" metal gasket that came as a part of a kit from SNG or Moss (can't remember). I have been reading a lot about head gaskets but I have not come across anything definitive. I'm not sure if I should use the gasket I have or if I should get a thicker composite gasket with the silicon seals around the water passages. My head required a good bit of welding and machining around the water passages and it was skimmed. The block also had some corrosion around the water passages and was decked. I don't know how much was removed from either but I think the block just got a kiss to clean it up. There is still some discoloration around the water passages but if feels fairly smooth.
I am concerned about sealing (especially around the water passages) and the bump in compression from the head and block machining. I'm all in with this car so ditching the gasket I have in favor of a $150 composite gasket is an option if you think it will help. Maybe I'm overthinking this.....

 

I have the composite Payen gasket on my 3.8 litre 8 to 1 car plus skimmed head (running on 95 RON gas ~ Not even a hint of knock at factory settings). I don't think there is anything wrong with their standard gasket. There was no rationale in this decision. I was satisfied my surfaces were perfect. I just shrugged my shoulders and bought the composite gasket probably because Alfa used them in my youth & I owned many Alfas. (8)

Payen gaskets were frowned upon as 2nd tier many years back but I think they make a great product today.

That did not help you at all. If you have the gasket use it. There are a hell of a lot of them out there ~ unless someone comes up with a sound reason not to.

I think the same old adages apply ~ clean & dry. Most head gaskets are micro encapsulated today. We are in the Nano era.

 

I've attached 2 spreadhseets developed by Ray Livingston on the Jag-lovers list and with a few measurements you can determine the compression ratio that will result from various thicknesses of head gasket, so then you can determine if the one you have is suitable or not. I'd aim for compression no greater than 9.2 using 91 AKI fuel.

The spreadsheets have the measurements for both head on and off. For the portion where you are measuring the cylinder volume I seal the edge of the piston to bore interface with a smear of grease. That creates a seal.

To measure the volume I use mineral spirits ( paint thinner) and use a small graduated cylinder. I have the block upright and level, then take a flat piece of glass to cover most of the cylinder, again sealed with a smear of grease against the top deck of the block and cover the bore compleley except for just enough to add the mineral spirits. Fill until the air bubble is gone and the cylinder is completely full. You should be able to get within 1 ml of the volume of the cylinder. Record how much you put in and what's left in the graduate when the cylinder is full, and the difference is the volume of the bore.

On the spreadsheets, only change values in red.

 

Clean and dry as Glyn said. Can't be too clean with a metal head gasket.
Check to see that the holes in the head where the studs slip through have no gunk in them that will come loose and contaminate the job when lowering the head onto the block.

 

Thanks, guys! I very much appreciate the input. I will do some measurements, see where I am and choose a head gasket accordingly.

 

I should mention that most of the numbers I have in the spreadsheet are for a 4.2, so double check bore and stroke for your engine and make sure the spreadsheet values are correct.

 

I think that is a very good point you make Jeff regarding clean holes in the head. As a matter of course/habit I just run a thin bottle brush through the holes & give them a blast of dry compressed air.

 

JB ~ this is wise advice if worries of knock are concerned on available gasoline & you don't want to over retard your timing. Our pumps & many others display RON. NA pumps generally display AKI (average between MON & RON)

 

I had a great time once rebuilding a motorcycle engine with an ex-Rolls-Royce, ex-RAF man who was then chief technician in a well-known university engineering group. He'd rebuilt Merlins during WWII. For him, cleanliness was absolutely top priority in all aspects of engine assembly. It went to the point that, he'd not allow an oily rag or a clean one that might produce a speck of lint or dust in sight.

 

Sounds as bad as doing a filter change on Benz 7 speed (722.9) & above transmissions. They provide you with a piece of Chamois Leather to clean the surfaces. If you don't it's amazing how often you experience a leak. The 5 speeds were the last easy ones (722.6) to DIY. Now much more effort is required.

 

When I was in the RR club we visited an aviation museum and I asked, "what's so impressive about 7000 horse power, they have car engines that will do that" ?
A car engine only sustains that for a short time, but a RR Merlin engine is designed to do that at a constant rate, or so I was told.

With that in mind, a small piece of lint or the tinniest fibre from a rag trapped in-between the head gasket fire rings at those sustained combustion pressures could be catastrophic.
A human hair is between 3 and 4 thou thick, that too would also pose a huge problem.

Were they still using copper and asbestos for their head gaskets back then, I would think that would be quite inadequate _ what were they using ?

 

The RR Merlin went through many generations some in mass production with Packard.

Many more head studs were used & surfaces hand scraped to tolerance and then silk thread and possibly a very thin liquid sealer was used as a "gasket". So no real gasket at one time in their life/development.

It's one hell of a long time since I've done any reading on the Merlin but this always sticks in my mind.

 

Hylomar was developed for the Merlin, intended as a (near) zero clearance sealant.

There is an aviation museum near me that is working a restoring a Mosquito and has a Lancaster on display. They are rebuilding a Merlin for use in the Mosquito.

 

I think Hylomar was produced for the Merlins but I did not know/remember as a head gasket material. Must scratch through my books but I'm renovating at present. We had started just before Covid. Lesson No1. Don't try & live in a house while renovating. Move out. We did not move out.

The Blue with slight green tinge Hylomar that I've used on Alfa gearbox casings etc. in the distant past has been a thicker substance in a tube. Today I prefer Yamabond as do F1 & racing teams in general.

Hylomar, of course, makes a range of products today.

 

I think Hylomar was intended as a gasket dressing, not a replacement for a gasket.

I feel your renovation pain, but we did the renos ourselves and didn't move out.

 

The blown Merlin's final low altitude hp was approx 2,030 ~ 2070. 7000 would have been burst hp.

 

I am probably one of the few people in this forum who has flown a merlin engine plane. I did it flying a Fiat G59 which was a post WW2 developed fighter just before jets became the thing. Performance was pretty close to Mustang and Spitfire contemporaries. Glen is correct that the last models were around 2000HP. There is no way 7000 HP could be produced.

Typical aviation practice for joining metal parts used the hylomar and silk thread which obviated the need for gaskets. That process can be still used today for joining crankcase halves in typical flat or "boxer" type engines used in light aircraft. Refer to Lycoming engines website. However there are also new different approved sealing cements which do not use the silk thread.

We used to coat the old tin head gasket with an equivalent to hylomar. It seemed to work OK. However the more modern gaskets like Payen don't need this as they have the "built in" sealant.
I fitted one last year to my MK1 and it is going OK.

 

Its good to have an Aviation man on the forum. Many developments of interest occurred in the aviation world that morphed into the automotive world.

In Racing including F1 there are two things all teams will carry. Duct tape (Gaffer tape) & Yamabond that was designed to seal machined facings with no gaskets & slight movement possible on motorcycles. Wonderful stuff. When time comes to split casings or whatever it just peels off. It's always in stock at Casa Ruck.

As Bill says most head gaskets today have a built in sealant. That is micro-encapsulation in the nano era.

An example would be a company launching a new perfume. They tell you to rub an area of the page in the magazine to smell it. That is an example of micro-encapsulation

 

As one who completed a RR engineering apprenticeship in Derby 1955-1960 I would like to throw in my 0.02c worth.
RR sealing compounds were developed in their chemistry lab under the leadership of a man called Squires. The compounds produced were thus called SQ-----.

When I was doing engine assembly on Darts, Nenes, and Avons, there were two compounds in use. One was SQ22 - a yellow coloured concoction used in lower temperature areas mainly on Darts and the other was SQ32 that was blue. SQ32 was the father of the Hylomar range and it also contained trichlorethylene for final degreasing of the surfaces. I seen to remember that it was used without gaskets on finely machined surfaces.
SQ32 was sold to a company for commercial sale as Hylomar. Unfortunately the modern version of Hylomar does not contain trichlorethylene as it is now a banned substance.
Back in the day, trichlorethylene was used in hot vapour degreasing tanks at RR and it was wonderfully powerful process albeit hazardous. I remember dropping a set of very black con-rods from my MG into a tank and being amazed when they came out grey.

I do not think that SQ32 was used in the days of Merlin builds.

TMI?

Bruce

 

Very interesting Bruce. You might just have proved many of the scribes wrong. We have a technical RR man living just over the hill from me who was there earlier than you & saw the Merlin era. He finally moved to Jaguar. I must ask him what he remembers out of interest.

Trichlorethylene or Trike in slang was used in hot vapour degreasing tanks up until 5 years ago in a well known global Brand plant in Cape Town. Man it worked well. The US parent just about had a heart attack & put an immediate stop to it. The reclamation of the area was expensive as it's contamination had spread far, wide & deep.