Twin Cam block

[vikebo]

Hi,

I am taking apart my Twin Cam due to increasing oil consumption.

It seems like there is a ridge in the cylinders. I have not taken out the pistons yet, but will get the cylinders measured properly.

The block is marked 691M (followed by 6015BA and T2).

I have not found a lot of information about this block on the net. A Ford magazine said it is an older block used for 1600 engines, and is weaker than the 711M block.

I installed a replaceable water pump kit from Burton a few years ago, and then I ordered the kit for the 711M. This turned out to be a bit too high and had to be machined off a few mm, so it seems to have a block height somwhere between the original and the 711M...

It does have 5 bearings and a 6 bolt crank.

The previous owner said it was bored to 83.5 mm, but a quick measurment said 83.26 mm.

Does anyone know the maximum safe bore of this block? Or should I start looking for a 711M instead?

Thank you for all help!

Eivind

[rgh0]

Hi Eivind

Sorry but I cant help much
In short blocks I have 681F and 701M and in tall blocks a 681F as the nearest matches on my list but no 691M so dont know much about it assuming the number is correct. The list I have came from this reference
http://www.lotus-cortina.com/library/block/blocks.htm which is the best listing of Ford 1500/1600 blocks I have come across.

Almost all of the Ford blocks will go to 83.5mm with careful boring. However depending on block condition and end point it may be easier to go to a new 711M block

Rohan

[M100]

3.25" or 82.55mm is the standard bore. The blocks should take 0.040" (40 thou) or 1mm overboring without problem.

83.26 is only 0.75mm overbore so there is at least one more rebore available before resleeving maybe becomes necessary.

The block height ought to be the same on all pre-crossflow blocks at around 7.91" or 201mm, the 711M block was never fitted to Elans and is as you've found quite a bit higher.

[vikebo]

Thank you for your replies. Seems like I can consider a rebore then, not sure how easy it would be to find a good 711M block in Norway.

I have had a look at the Cortina site with the blocks earlier, but thanks anyway.

Can add that the original front cover was approx. 1/2" shorter than the 711M version from Burton. It had an aluminium spacer of approx. 1/4" (which is the reason why I thought I needed the tall version). As said before, I had to cut it down approx. 1/4" to make it fit.

BTW, I am quite sure it is marked 691M. The picture is not very good, but...

http://www.home.no/vikebo/bilder/691M.JPG

Eivind

[types26/36]

As far as I remember the Mk 1 Capri (1600 Xflow) was fitted with the 691M block, not sure what the difference's are to the 711M, as someone said the 681 blocks were available as 1500 or 1600. The 681(1500) was fitted to Elans and TwinCam Escorts before the 701M.
I also seem to recall the 681's had the round main bearing caps while the 701/711's had the square m/b caps, what does your 691 have?
I have bored the 681 to 84mm and 711 to 85mm with no problems, the stongest block came after the 711, it was a 831C and is known as the AX block by some people although all 831C blocks are not marked with "AX"
Generally speaking the numbers 68 (69) (70) (71) (83) refers to the year in which Ford first used it and the number (1) refers to the type of engine (Kent) .........and befor I'm shot down there are some exceptions to this rule.
So in conclusion it sounds like you have a 1600 Capri block modified to fit in an Elan.
Regards Brian

[vikebo]

Interesting to know what the numbers actually mean.

Regarding the caps, I am actually not sure what the different types look like. Do not think I have found any pictures of the round type, but I think mine look like the square ones Wilkins has got in his book. But the ends are round...?

http://www.home.no/vikebo/bilder/caps.JPG

I have to admit that the Twin Cam is in a Seven, not in an Elan... ...but I have not found other forums with the same knowledge of Twin Cams.

Eivind

[types26/36]

[quote="vikebo"]
I have to admit that the Twin Cam is in a Seven, not in an Elan... .......

Those are the square m/b caps (stronger) type and as for the Seven T.C...........
I also have a Seven with a 711 based T.C. (85mm)

Should you go for a 711 just check it is a 1600 (BA) AND NOT A 1300 (AA)
Brian.

[vikebo]

Thanks, good to know I have the stronger type.

I will try to keep in mind that I need the BA type if I replace it.

Would it be possible to use a 831C block? Any reason not to?

Well, I did a quick search, and it seems like they could be hard to find if this info is correct:

http://www.apexspeed.com/forums/printthread.php?t=13826

Eivind

[types26/36]

[quote="vikebo"]
will try to keep in mind that I need the BA type if I replace it.
Would it be possible to use a 831C block? Any reason not to?

There is no reason why you cannot use the 831C (if you can find one) it is basically the same diamensions as the 711 although it has two dipstick holes (well thats not altogether true) it has the normal dipstick but it also has a "hole" for a oil level sender, they were made in S.Africa and used on the Seirria/Saphire range of cars as S.Africa did not have the Pinto 1600 engine, it only got the 2.0 litre Pinto engine.
When Ford S.A. ceased production of the Kent one of the tuning company's from the U.K bought up all the excess stock of 831C's and they were sold as thick walled FF engines (at a high price) so if you want to get one a trip to the scrapyards of S.Arica is an option
The normal decking of the block/longer timing chain/alloy spacer etc is required to fit it to a T.C. although as you know Burtons supply a "tall" front cover and backplate.
Regard Brian
P.S. I've got a 831C under my bench in S.A.

[vikebo]

Well, guess I don't really need a 831C. But fun to know about anyway.

A trip to S.A. could be fun, but I guess the airport staff would think it was some kind of weapon if I brought a block as hand luggage.

Eivind

[Foxie]

Hi,


I installed a replaceable water pump kit from Burton a few years ago, and then I ordered the kit for the 711M. This turned out to be a bit too high and had to be machined off a few mm, so it seems to have a block height somwhere between the original and the 711M...


Thank you for all help!

Eivind

Just a caution re your conclusion above, I think all tall front covers come a bit taller than even the 711M so they can be machined level with the deck, to get it exactly level.

Sean Murray

[Dag-Henning]

- as far as I know , front covers are never level with the deck, as the front-cover to head gasket is thicker than the block to head gasket......
The cover "always" sits below deck height. Eivind, call me on 922 66 321 if you need "moral support" - I may have some help to offer.

Dag ( Oslo )

[vikebo]

Sean and Dag-Henning,

I called Burton at the time, and they wanted to swap the covers to the lower type. It didn't sound like they usually machined the covers. Because I was about 1300 km from home and had a week to replace the covers, swapping would be too slow. They then said machining the covers would probably work out OK when I suggested it.

I think it was someone at a company called cyliderservice who based on the thickness of head and front cover gaskets said the front cover gasket would compress enough if the front covers where level with the block. As far as I can remember, my covers turned out a few 10ths of a mm lower than the block. However, I think you are correct, a larger different would not hurt, but how much...

Thank you for your offer of moral support, good to know. I think I have been talking to you on the phone before.

Eivind

[rgh0]

The Elan Factory stocks 3 different thicknesses of front cover to head gaskets so you can match it up properly depending on the step size at the block when you have aligned the front cover to the crank properly and how thick a head gaskets you use. Other engine builders like QED may do the same.

Rohan

[vikebo]

OK, nice to know.

BTW: classicford March 2005 has got some info on blocks in a Ford Kent Crossflow article, but not everything in this thread.

Eivind