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6pack

150BHP v 125BHP

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Unless you have a gearbox with ratios suitably spread so that the overdrive ratio falls optimally between the gears (which it doesn't really) using overdrive fails to make the box a true 7 speed in the case of the CP or a 6 speed in the case of the CR - 2nd and 3/4 isn't that useful a gear and personally tend to only use mine in 4th gear as a cruise option as you would 5th in a modern car. The power band is wide enough on both.

 

One of the more frustrating things is that the gearbox mountings on the chassis are different for the CP and CR cars so the two gearbox/OD combos are not interchangeable without modifications.

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Of all the cars I drove I couldn't tell the difference except for the overdrive on the J type seeming as already pointed out to having a more civilised engagement.

Mine, a CR revs to the redline very easily....except in top. It could really do with a rev limiter. Not the most refined 6 pot motor but who cares!

Agreed on the throttle linkage though a bit of a pig to get set up, but once you get the hang of it it's straight forward enough. (Providing the TB's are sitting inline and level. I made an alignment tool to get it right. )

Anyway whatever you get its a grin a minute!

Personally I like the instruments of the earlier cars, but, I hated the floor mounted dip switch.

Tried to get my partner to photograph the speedo and rev counter today.... She refused said it was incriminating!

Edited by daven

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I also agree with Kevo, to the best of my knowledge the CP engines from CP75001 had the recessed block and accordingly the rimmed cylinder head gasket! These later CP engines also had single valve springs too whereas at CR 1E they went back to twin springs like the pre CP75000 series. Comments Neil please, oh great TR oracle and sage.

Cheers

Alan G.

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150 or 125 BHP - well 2 different measuring standards (SAE and DIN) and nowhere near the 25bhp the numbers might be assumed to imply.

 

Glad someone bothered to note this, just in case someone thinks its OK to compare 150 apples to 125 pears.

 

Funny how most people seem to go bhp blind over this :)

 

Alan

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Unless you have a gearbox with ratios suitably spread so that the overdrive ratio falls optimally between the gears (which it doesn't really) using overdrive fails to make the box a true 7 speed in the case of the CP or a 6 speed in the case of the CR - 2nd and 3/4 isn't that useful a gear and personally tend to only use mine in 4th gear as a cruise option as you would 5th in a modern car. The power band is wide enough on both.

 

One of the more frustrating things is that the gearbox mountings on the chassis are different for the CP and CR cars so the two gearbox/OD combos are not interchangeable without modifications.

I'm glad it's not just me

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There are some fundimental differences between A type & J type overdrives:

 

A type: Is 'Slam' engagement, this was designed out of the J Type. Not very good for the drive train! It. Laycock tried to lessen this effect on the TR4 IRS but the problem was not fully sorted until the J type. Also suffers from poorer oil filtration. Often the cause of not working properly

 

J Type: is progressive engagement, it has no accumulator, as it is meant to be! Yes it is not as ruggedized but it does not have to be, because of its method of engagement. Volvos usually clock well over 200k on these units if oil is changed regularly and filters are cleaned.. It has much better oil filtration than the A type. Operating on 2nd gear is not recommend as per our Forum nor by Overdrive Repair Services, as I was going to go down this route.

 

Power difference between 125 and 150. Years ago we checked this out using the DIN Scale only on a rolling road and we came up with 10 + BHP! We also suspected that the CR may have had a heavier flywheel?

 

Bruce.

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Glad someone bothered to note this, just in case someone thinks its OK to compare 150 apples to 125 pears.

 

Funny how most people seem to go bhp blind over this :)

 

Alan

Well I never new that :o after all these (on off) years of CP TR6 ownership…………..so glad I made the choice I did based upon the fact that I preferred the earlier style of dashboard :D

 

ATB Graham

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I use 2nd gear O/D all the time in my cars, both Webered with more power than the stock CP P.I. cars. Normally I let off the throttle for that crucial nanosecond to spare the drivetrain the shock of engagement - then take it up to 70 mph before shifting if I want, often skipping 3rd. I've been doing this without reason to regret for well over 100K miles, never failing an O/D unit nor breaking the diff moorings. I would estimate its contribution to the O/D fun quotient at 50+%.

 

In the higher gears I don't worry about engagement shock; the delivered torque is much reduced from that of 2nd gear.

 

My show car has the triple roller bearing laygear and reinforced diff mounts. It has bested V8s of its era in drag matches using 2nd O/D with the pedal to the metal, no throttle letoff.

 

Cheers,

Tom

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The J type may last a long time in a Volvo, but attached to a Triumph box it will probably get its oilways loaded with debris when the layshaft bearings or other bits go up the shoot so likely to need clearing out long before that 200000 miles that it would be capable of.

 

Putting the gearbox back in the CRs may be a tad easier because to the different rear gearbox mount.

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Andy,

 

Laycock O/Ds were fitted to many other makes and models besides TRs, Volvo being one of the largest. Saloon Car drivers do not like slam engagement.

 

J Type:---That is not only my opinion its the opinion of a number of O/D repairers here in the UK/USA!

 

If you have not done the Stag/ Police 2.5PI Mod to your to your Lay Gear and replaced the Lay Shaft with a properly harden shaft, there are still soft ones being sold in the current market place, you will always have trouble!

 

I have just reported this problem to the Register.

 

Bruce.

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The point was that the longevity of the overdrive unit is not just determined by the overdrive but also by the gearbox bolted to it and the vehicle it is fitted to and the amount and type of use it gets. (The layshaft example being one example of how a poor design and poor quality parts in the gearbox can leave a robust item (both the A and J types) being deemed unreliable)

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Andy,

 

Register members should push the Register for the lay shaft to be made out of EN40B Steel and then Nitrided,( this method is used in Jaguar Gear boxes). This is not a complicated part to manufacture and with the 3 needle roller bearing conversion to the lay gear. I feel that this problem would be a thing of the past.

 

Bruce.

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The block has a recess, not the piston, that is plain.

The recess is for the gasket that it can "grab" into the block

and keep its position better while especially in the area between

two cylinders the gasket is small and the pressure difference

wants to push the gasket to the side or pressure wants to pass

that little way between the cylinders.

 

When I do my displacement increase to 77 or 78 mm I have

to sacrifice that recess, what was a good idea.

With a good quality gasket that does not become a problem

although I increased the problems by the space between the

cylinders become smaller and compression ratio becomes higher.

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I wonder if the U.S. carbureted engines use the same gasket with the recessed bores, or the earlier flat one. As c/r dropped to 7.5:1 did the recess play a role, or were those heads just thicker?

 

Cheers,

Tom

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I wonder if the U.S. carbureted engines use the same gasket with the recessed bores, or the earlier flat one. As c/r dropped to 7.5:1 did the recess play a role, or were those heads just thicker?

 

Cheers,

Tom

The heads decide compression ratio

the bottom decides which gasket to use.

You are free to mix that all as you like

only correct gasket supporting the block is required.

 

On the heads the thickness gives the CR

So you can make a CP from any head if the inlet porting is the wide one

Smaller outlet valves can be kept as Witor recommends or cut to the bigger ones.

The advantage of the smaller valve head is that you often get a better porting from

combustion chamber to outlet port in the valve area if enlarged.

If you keep them the advantage is more material between inlet and outlet

to get it more rigid against cracks in that area.

If you already have a crack you can fit valve seats for inlet and exhaust in many cases.

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Reading the comments on the overdrives between 'A' and 'J' type I cannot say I have noticed any 'snatch' when engaging on my TR4a.

 

Having said that I have not experienced a 'J' type in practice but my 4a overdrive appears to be a smooth transition in 2nd, 3rd and 4th. So is it possible that worn overdrive clutches or low oil could contribute to such an issue and give variation in smoothness of engagement ?

 

Regards

 

Kevin

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Reading the comments on the overdrives between 'A' and 'J' type I cannot say I have noticed any 'snatch' when engaging on my TR4a.

 

Having said that I have not experienced a 'J' type in practice but my 4a overdrive appears to be a smooth transition in 2nd, 3rd and 4th. So is it possible that worn overdrive clutches or low oil could contribute to such an issue and give variation in smoothness of engagement ?

 

Regards

 

Kevin

Later A types for IRS cars are modified to give less snatch on engagement to save the axle mountings, leastways that was the original idea!

Stuart.

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Steel helmet on at 45 degree angle against blast...incoming.

Mick Richards

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On 6/15/2009 at 11:44 PM, johnmac said:

Hi 6PACK,

just to add some more details to the 125/150hp differences. The CP cars with overdrive used the A type o/d unit which could take more power so had overdrive on 2nd,3rd & top. The later CR cars used the J type (by memory) on which they only allowed 3rd & top to engage but this was balanced by a closer ratio gearbox.

I purchased my TR6 nearly 30 years ago and by shear luck purchased a very late 1972 CP model. I did not know then that his is perhaps the most desirable of 6s because it uses the later gearbox with early overdrive giving the best standard performance of any TR6 with 150hpSAE, close ratio box, 3 speed overdrive.

I subsequently gas flowed the cylinder head and fitted a 6into2 S/S exhaust manifold feeding into a standard S/S silencer and I find this very good, plenty of power with excellent low down torque making it very drivable but with the original TR6 sound. It does tick over a slighty irratic but still below 900RPM.

Suspension is standard except for some polyurathane bushes and spax telescopic conversion to the front & rear. It seems to work very well on the road, great fun when pushed hard.

I hope this is of interest and helps your choices.

Hi John,

The A type overdrive was changed to a J type on Volvo's wishes as they were GKN's biggest customer, because they did not like the engagement of the A type, even though GKN-Laycock  modified the A type a number of times to try to improve the engagement, in fact nor did BL as it lead to too many drive train warranty claims. The J type engagement is based upon the slipping clutch method. Regarding power! Volvo used a 3 litre V6 engine with the J type which was a lot more powerful than the 2.5 CP engine! My J type lasted 44 years before it was reconditioned by ORS as they also did my gearbox because the lay shaft was on its way out, the usual fault with the TR gearbox, which they modified to a 3 bearing Stag type. The Stag gear box is the best  gearbox for a TR!

Bruce,

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Interesting discussion about overdrives...

I have an A type on my TR6, CP series. My Reliant Scimitar, powered but a 3 litre Ford V6 has a J type O/D. The J type is indeed smoother engaging and disengaging.

But the worst of all is the D type fitted to my GT6. Without real care, it will thump in and out. Of course the D type was never fitted to TRs, as it's not strong enough.

No question, the J type is the best overdrive.

Nigel

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23 minutes ago, Nigel Triumph said:

Interesting discussion about overdrives...

I have an A type on my TR6, CP series. My Reliant Scimitar, powered but a 3 litre Ford V6 has a J type O/D. The J type is indeed smoother engaging and disengaging.

But the worst of all is the D type fitted to my GT6. Without real care, it will thump in and out. Of course the D type was never fitted to TRs, as it's not strong enough.

No question, the J type is the best overdrive.

Nigel

Nope

A type all day long.

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