Fo8 Gaskets

[RobinTR]

I have seen some interesting historic threads on how to remove and refit the wet liners in the Triumph engine, but I did not spot anything specifically addressing the Fo8 gaskets.

 

Moss have two types... P/N 112789 in steel and 112789C in copper. My 4A motor is in bits following leakage of water into the sump... the old steel Fo8 gaskets had thinned in a few places, so is it better to use copper for the rebuild? However, would the copper type take repeated torque down, as suggested by at least one of the forum contributors?

 

The removed liners/pistons seem to be in reasonable condition (I had the engine re-bored about 30 years and maybe 30-50k miles ago). At that time I also invested in a spare set of 87mm AE Hepolite liners/pistons (I was told that these would not be available in the future... little did they know the growth of classic car parts availability!).

 

Fitting the NOS AEs should see me out; but have there been any subsequent improvements in the design of the Fo8 gasket? The AEs come with what looks like a copper gasket; would it be best to stay with these, or use newly available steel or copper type?

 

 

 

[RogerH]

Hi Robin,

the steel Fo8's are apprx 0.015" thick, copper is apprx 0.018" and ali was about 0.023. The Ali appear to have vanished.

 

If you only need 0.015" gaskets then fit the steel ones. Yes they do corrode but take a considerable time - 20, 30 years.

My last set of steel Fo8's lasted 17 years and were not bad when I took them out.

 

If you go with Copper then I wouldn't panic about re-torquing for whatever reason.

 

Whatever you use, use plenty of Welseal jointing compound and good quality Antifreeze with rust inhibitor.

 

Roger

 

PS - welcome to the forum. Where is home.

Edited May 20, 2016 by RogerH

[RobinTR]

Thanks for the quick reply and information. I have ordered some Wellseal from the web, so will use that when it comes to refitting the liners. First I'll try to dry assemble the liners to assess the likely protrusion. Do you have any idea about how much the Fo8s compress when the head is fully torqued down?

 

I am with the Windsor Forest group... could easily walk to the meeting venue, but I have only been a couple of times because the TR has been off the road for years... or at least not much more that the occasional run to the MOT (did not trust the engine because of the small coolant loss), so I hope that will be solved by the time it all goes back together.

 

I have another head related question, but will raise that as a separate topic

[Motorsport Mickey]

"Do you have any idea about how much the Fo8s compress when the head is fully torqued down?"

 

3/5 ths of buqqer all !

 

Any settlement found is in the seating of the liners on the gaskets. Make a note that the 3-5 thou liner height shouldn't be meant to allow one liner to be at 3 and another at 5. That is the range of liner heights when fitted as sets 3.3.3.3 - 4.4.4.4.- 5.5.5.5. are fine, any variation between liners or across the liners allows a variation in clamping force where the liner height is less and a potential gasket fail point. Subject to you not having turned the engine over with the head off (it may displace the liner on it's seat, lifting it) use a depth micrometre to check the liner heights before you progress further, at 4 points around the liner onto the block. (depth mics are cheap on e bay) or use a straight edge and feeler gauges if you use them.

 

Mick Richards

[RobinTR]

Mick, Thanks for the additional advice. I checked the protrusion with straight edge and feeler gauges before pulling out the original liners. Admittedly not at all four cardinal points... readings typically around 3 thou, but I had not cleaned any old gasket varnish off the head. I will repeat more thoroughly during reassembly.

 

My question about compression of the Fo8 had been prompted after seeing that the Moss steel gaskets are 15 thou while the copper versions are 18 thou... so I had a assumed that the thickness of the latter was to include a greater compression allowance.

 

Incidentally, I found a useful set of fitting instructions on the web (for the new Moss heads). This certainly goes into the sort of detail which is missing from my original Standard-Triumph workshop manual!

[Motorsport Mickey]

Do a search for liner height on the 4 cylinder forum, there's at least 8 threads with various questions answered including all possible permutations on how to do it right ( I know, I posted them !).

Beware of trying to shortcut the tedious "fit liners-measure protrudence-remove liners -measure FO8-calculate FO8 gaskets needed for correct liner height and buy (prefer copper but unless you're 30 years old steel would do)-refit FO8s dry without Wellseal-measure liner heights, if not within the 3-5thou range buy appropriate thicker FO8s or machine liners down to figure required. Then reassemble this time with Wellseal measuring and checking as you go and get on with the build.

There's too much dynamics in the system to trust a one build and measure and then reassemble the chosen components into a correct liner height assembly, something always affects something else, slow and steady gets there in the end.

 

Mick Richards

[BuyBritish]

Hi Mickey we have a Morgan plus 4 fitted with a TR4 engine that has been rebuilt by a now non existing engine rebuilder.

 

We have driven 200 miles and find from the outset that perhaps timing was out as we experienced some pinking, but of more of a concern is the 'rattle' we hear when the engine is accelerated or goes under any stress ie up a hill.

 

The water is up to 90 degrees and she does get hot, tried compression on all cylindrs and we see around 160psi on all cylinders

 

Do we have head gasket or liner issues?

 

I guess to really tell it could be head off and measurement of the liner protrusion?

 

It sounds like a rattle but only under engine strain / power, I was thinking loose cam chain but its at not happening when reving engine up on the driveway...no noise at all, only when under load and turning the rear wheels.

 

Any ideas please

 

IMG_2497 by Robert & Ali Davies, on Flickr

 

IMG_6455 by Robert & Ali Davies, on Flickr

 

Rob

[Motorsport Mickey]

Hi Robert,

 

(Got that off the photos, hope correct)

 

Unlikely the liners or Head gasket are causing the "rattle" still sounds like a timing problem, retard the ignition on the distributor, either dynamically with a gun or by loosening off the distributor clamp and setting the engine off the crankshaft pulley to the workshop settings and see if that resolves it.

When under acceleration or hill climbing the engine is "loaded" most, hence pinking or detonation is most easily heard then, retarding the timing will help avoid that problem if that's what it is.

 

Mick Richards

Edited April 8, 2018 by Motorsport Mickey

[TR 2100]

If the engine rebuilder is now a "now non existing engine rebuilder",

that's a bit worrying.

It's a pretty basic engine but even so, many claim to be "experts"

but get something wrong.

 

Mickey knows his stuff - waaay more than myself, so easy to go along

with his comments.

 

I will only add that a newly rebuilt engine does generate a fair bit more

heat due to friction while components are bedding in, so don't be too

worried to quickly.

 

AlanR

Edited April 8, 2018 by TR 2100

[Ade-TR4]

Had weird problems on my father-in-laws rebuilt engine. Could never get it running right - persistent timing problems. Turned out that the cam was 1-tooth-out on the timing chain...

 

Re: liners and Fo8s, when I replaced mine, the first set of liners were not parallel between machined seating surface and top of liner. It was the seating surface that was out, so couldn't be corrected simply by grinding top surface. Had to return for different set (which were then spot on).

 

Cheers

ade

[Motorsport Mickey]

"the first set of liners were not parallel between machined seating surface and top of liner. It was the seating surface that was out, so couldn't be corrected simply by grinding top surface"

 

That's a weird one, never had a badly machined set of liners in maybe 15 used for rebuilds where new liners sets were used, "cooking" engine rebuilds as well as race engine builds where the components might be thought to be better machined.

 

Care needs to be taken to identify the correct problem, after 50 or 60 years use the blocks Figure of 8 machined "shelf" surfaces where the liners sit are often "leaning" within the block sometimes by a thou or more, having been "stress relieved" by thousands of hot and cold cycles and the passing of time.

I've had to have 3 blocks machined upon their Fo8 shelfs back to square and regain whatever integrity there remains, but avoided having to rebore the lower spigot area in the block the natural slide clearance there allowing the liner to fit and seat naturally. If the Fo8 shelves are left leaning they naturally drop the top liner surface but compounded around their circumference, many owners fear this area of renovation and reluctantly accept that achieving a parallel liner top square in all planes and level with all the other liner tops and achieving an equal gasket crush and clamp is too difficult to achieve...it isn't.

 

Mick Richards

[Ade-TR4]

Weird I know, but checked at my Dad's engineering shop - definitely out. Second set were OK.

Ade