'74 TVR 2500M

Stu Lasswell said:

In reply to dherr (Forum Supporter) :

And I really want to avoid a cutting/welding project, as I don't have the skills or equipment (like Scott) so that job would have to be farmed out as well.

If you want to pack up that frame and ship it to me, I will happily do the same mods.  No charge or anything, just whatever it costs you to ship.

In reply to TVR Scott (Forum Supporter) :

   I can only assume that you are being facetious. At this point I really believe the conversion can be done without the cut/weld option. Didn't get ahold of Richard Good today, but I'm feeling good about the trimming of the isolators being enough.

   In other news, I can say that there is a weight limit to what those cheap Harbor Freight saw-horses can support, I tried nudging the TVR frame over a couple of inches to get my TR3 out for an autocross tomorrow, and both saw-horses collapsed, dropping the frame to the ground. I guess I didn't fully take in to account how much weight I added by fitting the suspension, brakes, steering, shocks, etc. Lost a couple of inches of skin off my forearm, but the TVR seems unharmed (brakes drums and disks/dust shields took the contact with no sign of damage). Back at it on Monday!  

In reply to Stu Lasswell :

Yikes!  That saw horse incident sounds no fun to me.

On the other point, I wasn't kidding. I'll totally make that mod for you if you need it.

This is GRM we do stupid things to help each other out.  We also do things like drop cars off saw horses.  Glad there isn't any major damage.  Next time I'm up there with time I want to check out the TVR and the TR3.

   I do appreciate the offer, Scott, but I think that transporting the frame from North Carolina to Colorado would negate any savings by having you work for free. If I am out that way, give or take a state or two, I might just try to drop in and see your project. So far in my travels you have been in a "fly-over state" for me.

   EDIT:  Upon further consideration, I guess you're just talking about the little sub-frame diff hanger... THAT I could see shipping your way!  Well, if my current plan fails to achieve the results I need, we may have to consider that option.

   Oh, and Stampie, you are most welcome to drop by any time to see any of my vehicles and projects!

In reply to Stu Lasswell :

Yes.  Just the sub frame.

I agree that shipping the whole frame would be a bit too much!

   I talked to Richard Good this morning. He actually tried to call me back on Saturday (twice!) while I was at the autocross.  Anyway, he says he sees no problem with cutting down the isolator bushings as long as I can avoid metal to metal contact between the mount and the frame. Richard says he has sold a fair number of these kits to TVR owners, and was a bit perplexed by Scott's issues with frame interference.  I think when I mentioned that Scott was not cutting down the flange and using the larger diameter driveshaft he finally understood. It may be a couple of days before I trial fit my diff, but obviously I'll post my findings and pictures.

   Well, I  put the frame onto the old TVR wheels, and officially made it a rolling chassis!  Then I thought, what the heck, let's just see how that differential will fit before I have the flange cut down to TVR/TR6 diameter.  I also decided to try it without any upper isolator bushing, since I anticipate having to cut it down to minimal clearance anyway...

It fits, although the input flange is literally resting on the frame member.  Still, it does prove the plan should work!

Here's a straight-on view. Again, there's no upper isolator, but I think that even with a quarter inch or so of bushing spacer I should have plenty of clearance once the flange is cut down to that scribe line.  In fact, I suppose I could have that flange and the drive shaft flange cut down even further without weakening it to any great extent, and have a bit greater margin of error.  It's going to work! Yay!

Thats fantastic!

Well dang, if i knew you needed the flange cut I could have done it in my lathe before i sent the diff

Patrick (Forum Supporter) said:

Well dang, if i knew you needed the flange cut I could have done it in my lathe before i sent the diff

I appreciate the thought, Patrick, but the flange needs to be cut down, 4 new bolt holes drilled, and a relief cut in the face to pilot the driveshaft flange. I'll get it all done locally, and have the driveshaft shortened at the same time I suppose.

    I got the flange and the driveshaft off to the driveshaft shop for the required modifications. Probably get them back next week. Duster (Michael) figures we should be able to cut the isolator bushes down on his band saw, so that should be no problem.  When I get these things all back into the shop I can put it together and (hopefully) be done with that part. In the mean time I'm contacting Sam Halkias about getting and engine built. Guess I can separate my old engine from the gearbox and make sure the 'box is OK. I've already bought new clutch components, so  that can be put together. Brake lines may be the next major challenge after all that... probably after the new year.

    My wife has asked me how much I've spent on this project so far... I tell her I haven't added it up yet. I probably shouldn't ever add it up. Ignorance is bliss, they say. If I were to guess, it'd be just under $5K. I can see tripling that amount before I'm done, if I'm lucky. More realistically quadrupling it... still, $20K for a ground up rebuilt (and improved) 2500M would not represent a crazy investment.  When I look at what I spent refurbishing my TR3 relative to the sheer enjoyment it's brought me over the last 21 years I have to consider it money well spent.  I expect to get my money out of the TVR as well!

I second don't adding it all up. You could spend much more with other hobbies, will have a great car when you are done which you will enjoy for many years. I always just give them that blank look and say I don't know but think of what I am saving by doing most of it myself :-)

I just finished sorting through receipts for the Mallard TR6 that I sold to my brother.  There's some useful info in there for him such as what clutch I used, but thinking about the cost is staggering.  If you add everything up, it's in the neighborhood of $24k in 1995 dollars, and that doesn't count my labor.  But given that I drove that car for 25 years and 30k miles, I believe it was worth it for the experience and memories that I have.  And now my brother continues to benefit from a well sorted car.

So carry on.

In reply to JoeTR6 :

Yup, that's pretty close to where I was when my TR3 was done back in 2004. Now, 90,000+ miles, multiple trophies (show and autocross), and too many friends to count later I can look back and say that my life was enhanced by the money spent on that car!

   Back to work on the TVR again, finally. Before Thanksgiving I took the driveshaft and the diff input flange to a shop for modification... prop shaft shortened 2.5", flange cut down and drilled.  Turned out the shop could do the driveshaft work ($50) but didn't have the equipment to mod the flange. Got a local shop to look at the flange, and the guy took me back into the shop and did it while I watched. A bit more involved than I thought. The relief that aligns the shaft (U-joint) on the flange has to be cut very precisely, and the bolt holes are not square, but rather in a rectangular pattern. Anyway, the work got done ($100) and I could proceed with the fitting of the diff to the frame and see if I was going to get the clearance I need. Oh yeah, Michael (Duster) was able to cut the isolator bushes down on his bandsaw... thanks, Michael!

Here's a side view of an isolator, after being cut... I think we removed about 3/8" from each.

A view of the cut-down flange installed, and the shortened isolator bushes can be seen above the mount, with full height bushes below. (I'd use arrows or circles to highlight where I'm referring, but I don't know how!) 

Then it was just a matter of dropping the diff mount assembly back into the frame to see if the reduced flange plus the shortened bushes would give me enough to clear that lower frame tube...

... and I would say YES!  Not much, but even with the drive shaft in place there seems to be plenty (well, enough) gap between shaft and tube. I could gain even more clearance if I add some spacers to the back mounts, but that will tip the front of the diff upward. I won't really know if I can get away with that until the gearbox and motor are in place to compare the angles at either end of the driveshaft.  Now, on to attaching the axles to the diff and and securing them in the hubs.

Fantastic!!!

And the bushings were a close enough guess for no metal on metal?

And the bushings were a close enough guess for no metal on metal?

   It looks like there should be no problems there, Michael. Good job estimating!

   OK, so I got the axles attached to the diff, and then secured to the hubs... other than fluids, the back end is done!  So, I figured it's time to get started on the rest of the drive train, as in gearbox and engine. So, dragged them out to the front of the garage/workshop, and separated them. Actually, the throwout bearing looks good, and the clutch plate has plenty of meat left... no matter, I've got brand new heavy duty clutch components waiting to go in.  Then I spent the better part of two afternoons stripping the ancillaries off the motor in preparation for exchanging it for a rebuilt unit.  Everything was pretty solidly attached, what with years of sitting idle outside.  Used lots of PB Blaster, but got it pretty much stripped.  I'm getting a Sam Halkias built motor... I could go into the details of what he offers, but suffice to say it should be in the 135-140hp range, built with all new or refreshed components and then run before delivery. I'll also most likely opt for a lightened flywheel and fan delete.

   Now, my question to you TR6 gurus and internet experts out there... how far should I go with this build, and where should the money best be spent?  For example, the basic "hot street" motor Sam offers is .020 over, 9.5 compression (regular gas) and runs Richard Good's GP2 cam. I'll be running the standard 2 Strombergs, but with a header and fairly open exhaust.  I could opt for a bit more compression, as I'm probably going to run non-ethanol fuel (90 octane) or premium (93 oct.) if necessary.

   The big decision... if I go for more, I'm considering either a) 1.55 ratio roller rockers or b) cam bearings and the GP3 cam,  Either option will add about $800 to the build.  With the 1.55 roller rockers I'll reduce friction, gain lift and maybe 10% more HP.  The cam bearings by themselves won't add horsepower, but add durability, and would be necessary for the higher lift cam and I could go up to 1.65 ratio lifters.  I talked to Richard Good, and he felt that the stock cam and even his GP2 cam should be safe without the cam bearings, but also felt that they did offer a margin of safety and longevity.  The 1.55 rockers add some stress (pressure) to the cam, but, again,"should be" OK.  Obviously BOTH would be better still, but that's a lot of money.  Or, maybe I'm chasing the wrong rabbit, and should pursue power/longevity/drivability via other means.

   So, internet oracles, speak your wisdom at me...

Keep it simple. Standard cam bearings have been proven pretty well for millions of miles. 

And if you decide later to get the other 10% from different rockers,  you can do that with the engine in the car. 

Also: i probably have an electric fan or seven in cold storage. Grab dimensions and we'll see whats up there before you spend money. 

In reply to Dusterbd13-michael (Forum Supporter) :

Well, Michael, the TR6 motor has no cam bearings stock, the cam rides directly in the block.  Also, the TR6 fan is not really useful as it is about 3 feet from the radiator in the TVR. They use two pusher electric fans, and I think only retain the stock fan for balance or damping.

Wow! Honestly,  only bearingless cams id ever seen were ohc engines with aluminum heads. You're going to send me down and educational rabbit hole there....

Is there any concern with balance getting rid of the mechanical fan? Or is that taken care of with internal balancing on the rebuild and an aftermarket harmonic balancer? Again,  im DEFINITELY out of my experience here now, so im going to sit back and learn.

The engine in my TR6 project is running a 10:1 compression, but the car I just sold was 9.5:1.  Both use the GP2 cam and have nice power off the line.  Both use standard rocker ratios, although I ran 1.65 ratio roller rockers on the sold car for a short time and the difference was noticable.  I put cam bearings in the new TR6 just in case I go for more lift later.  IMO, this setup is fine for a hot street motor.

The autocross car back in Virginia is a more extreme example.  It has 10.5:1 compression, 1.65 rockers, .040 over pistons, GP3 cam, exhaust header and fuel injection.  Even with DCOE 40 Webers, it could run 93 pump gas with a more aggressive than stock timing curve.  But that engine also ate a cam and had to be rebuilt.  The stock lifters are quite small, so get the highest quality ones you can find.  That car will keep pulling up to the 6200 RPM redline and makes for a great autocross car.  The only thing I'd like to try but never did was a GP2 cam in that motor.  The lower torque band may be just as fast for autocross without reving the engine past 5800 RPMs, but I have no data to prove it.  For a track car, definitely go with the GP3 cam.

Dusterbd13-michael (Forum Supporter) said:

Wow! Honestly,  only bearingless cams id ever seen were ohc engines with aluminum heads. You're going to send me down and educational rabbit hole there....

 

Is there any concern with balance getting rid of the mechanical fan? Or is that taken care of with internal balancing on the rebuild and an aftermarket harmonic balancer? Again,  im DEFINITELY out of my experience here now, so im going to sit back and learn.

What really blows my mind is that the cam bearings retrofitted to a TR6 motor come from a Spitfire.  Sure, the TR6 motor is basically the same but with 2 extra cylinders, but the cam/rocker geometry is the same FWIK.  I suppose the extra cost of line boring the longer TR6 block for cam bearings would have broken the factory's budget.

There shouldn't be an issue leaving off the fixed fan.  Balancing the rotating masses helps smooth out vibration, but there are nasty crankshaft harmonics at higher RPMs thanks to the 4 main bearing design.  Much over 6200 RPMs can rip the flywheel off or break a crank.  GoodParts sells an ATI damper that I installed on the Blue TR6, but it's only reved up to 4000 so far.  That could be fit later if problems arise.