Advice? 1973.5 Engine Work, leakdown- VT/Mass

[lespaul]

I have a 1973.5 T with 185,000 miles. It has never had a top end job or any engine work. Records show regular oil changes. Until a few weeks ago, it was running fine. Now, upon deceleration (and especially when engine is "braking" on long down hill runs) it blows a lot of bluish smoke. Another big smoke cloud upon acceleration -- but then with steady running the smoke disappears. It also seems to be running much hotter than it used to.

From reading the threads, I am guessing I have a bad valve guide (or guides). With a car with this many miles on it, I may have other engine issues that should be dealt with. So, before I dig into either a) just replacing the guides, b) doing a top end rebuild, or c) doing an entire rebuild (ouch), I think I should have a leakdown and a compression test performed. I am hoping that these tests will help me pinpoint whether I have a bigger problem than just valve guides. For what it is worth, the prior owner's records show a compression test done at 125,000 miles with 130 lbs compression on all cylinders.

Does this make sense? If so, specifically what should I ask the shop to do? And, can anyone recommend a shop in the Southern Vermont/ Western Mass area to do a good leakdown and compression analysis?

[Grady Clay]

Brad,

Good plan.

I suspect your preliminary diagnosis is correct: the smoke is from worn valve guides. It can also be worn pistons & rings. You probably can’t tell for sure without disassembly.

The compression and cylinder leak tests will give you additional clues.

At 185K mi., you will greatly benefit from a complete rebuild. While expensive, it is something you can DIY with the support of this Forum.

There are many normal maintenance items and upgrades you can perform. Most important are the chain ramps and chain tensioners. The heads can be made ‘like new’ and better with new valve guides and a proper ‘valve job’.

You will probably find the main and rod bearings in excellent condition. Their replacement is to insure another 185K trouble-free miles.

You need to make an ‘Executive Decision” regarding the pistons & cylinders. Yours will no doubt be out of spec and not repairable. I recommend modifying to use the ’73 911RS 90 mm P&Cs. These are the later technology Nikasil aluminum cylinders and forged pistons. They will increase the displacement from 2341 cc to 2687 cc while raising the compression ratio from 7.5:1 to 8.5:1. While requiring premium (pump) fuel, this gives a significant increase in performance.

You need to consider the overall condition of your 911 (rust and prior collision repair). You also need to consider your intended use. Generally speaking, this king of rehab is very worthwhile.

This may also be the opportunity to rejuvenate the 915 transmission and generally maintain the suspension. Features like the 911SC front oil cooler and 1.82:1 engine fan ratio help extend the engine life more than original.

Best,
Grady

[scarceller]

Do the leak down and comp test while at it - if these 2 tests show decent leak down no more than 7-8% leak and the cyl Comp is within 10% across each cyl then most likely the issue is the valve guides. But if the leakdown or comp test finds/indicates bad cyl(s) 1 or more then you know it could be below the head in the cyl.

Also, cracked rings from possible detonation could also cause large amounts of oil to flow past the cyl/piston.

[lespaul]

Thanks Grady and Sal,

I like the idea of a complete rebuild, but I think I will take this one step at a time.

I read a thread that said if the simple compression test was positive, there is no point in doing the more touchy and expensive leakdown test. Do you have any views on that?

[scarceller]

Originally Posted by lespaul

Thanks Grady and Sal,

I like the idea of a complete rebuild, but I think I will take this one step at a time.

I read a thread that said if the simple compression test was positive, there is no point in doing the more touchy and expensive leakdown test. Do you have any views on that?

The comp test is a good simple test, so long as you are above 120lb each cyl and all 6 are within say 15% of each other then most likely the cyl/piston/rings are OK. But the leakdown is also useful if you have the tools to do it.

One more thing: if you are seeing that much smoke on decel I'd bet a simple spark plug removal after a good long decel would quickly find the problem cyl(s) just by looking at the plugs.

[Elombard]

Another option might be to slide in a used 3.0 CIS motor and then take your time on that fantastic 2.7 that Grady describes.

I think the SC motors are a very easy install on the 73.5 cars. Oil cooling may be an issue though.

[Grady Clay]

Brad,

The compression test and cylinder leak test are complementary. Much of what they tell are the same. The advantage of the cylinder leak test is it can tell you where a problem exists. It also gives an quantative number to compare against other engines.

The combination of both tests gives you better ability to make the best decision for your situation. You want to make sure the issue is only worn valve guides or rings and not broken rings with impending (and very expensive) failure.

Given your situation, I recomend you perform both tests and then drive an extended 'sporting drive'. A re-test will tell you a great deal about wear or dis-use.

I agree, installing a 911SC 3.0 is an easy solution. The key is to find a suitable engine and not just buy someone else’s problem. Installing a 3.2 Carrera with its attendant electronics is also a reasonable possibility.

Regardless of other engines, your 911’s value will best be maintained with your original engine. It is very useful to have another engine as a ‘place holder’ while you rehab your original. This keeps the car operating. No 911 likes long periods of inactivity.

Another possibility to consider is to build yourself a ‘hot rod’ engine while your 911 still runs (abet with some smoke). You can start with almost anything. It is only limited by your imagination and pocketbook. It is perfectly reasonable to start with a 3.0 or 3.2 and build a large displacement, high compression, S-cam fun engine that easily swaps in and out of your 911.

Regardless of your choice, adding a front 911SC oil cooler and sourcing the components to have a 245 mm 1.82:1 fan will extend the service life of your 911.

Best,
Grady

[lespaul]

Grady, good idea on the 3.0 substitute while I turn my original and matched engine into a 2.7.

Any idea what a sound 3.0 would cost me?

[Grady Clay]

Brad,

I’m not current on valuations but many others on the Forum are. I’m sure you can find a suitable 3.0 engine at a reasonable price. The key will be inspection and buying from a responsible seller. This will give you the time to rehab your ’73.5T to whatever specs you want and have a 3.0 left to hotrod afterwards.

Perhaps you can find a local Pelican to lend you an engine. If you were local, I would have a ’79 911SC 3.2 possibly available. Engines, just like our cars, need constant exercise.


I may get flamed for proposing the 2.7 P&Cs for your ‘T’ but the option of original iron cylinders and cast pistons just doesn’t make sense to me. Technology has progressed.

Best,
Grady

[Elombard]

Brad I think you could get a pretty solid motor and all the parts for $4k if you DIY the install. Possibly $3K if you are willing to accept a higher mileage motor that leaks a little or something.

I bought a well maintained 3.0 but with high miles for $2700 a few years ago and sold a great running low compression on one cylinder core 3.0 for $1700 or so. I think the new owner of the "core" motor abused it for several more years with no issues :-)

[lespaul]

So --- I did the leakdown test yesterday. Ran it with engine warmed up. Here are the readings Cyl 1 = 9.5%, Cyl 2 = 7.5 %, Cyl 3 = 2%, Cyl 4 = 8.5 %, Cyl 5 = 9.5 % and Cyl 6 = 7.5 %. I ran the test on some cylinders several times to just make sure the readings were consistent. They were.

I am new at this, but from what I have read, these seem really good for a car with 185K on it and no engine work ever. If this is good, what is causing my blue smoke on deceleration (please read thread below)

I did put some SeaFoam in the gas and oil before the smoking started in earnest. Could that have thinned the oil, letting it get past worn valve guides that are not so worn they need to be replaced?

I am thinking maybe to run the current tank of gas out (at night). Then change oil and do a valve adjust while I am at it. Then see what the story is.

One more clue. When I pulled the plugs to do the leakdown test, my number 3 plug was wet with oil. The other plugs looked perfect. Funny thing is the number 3 cylinder had the least leakdown.

Also -- what is causing overheating?

Any ideas on where to go from here?

[DanielDudley]

I would try the simple stuff first. Change out the oil and put in new plugs. Check the wires, cap, rotor and points if you have them. Most likely you will still have a problem, but I don't see how Seafoam could ruin your engine, and the co incidence is too clear.

Also, did you say that it stops smoking if you run it for a while, or does it happen all the time ? I am not one of the smart guys, but there seems to be something missing here.

[gerry100]

Try Rick at R&D Automotive , just over the border in Albany.

(518) 598 1273.

Many years of experince and an enthusiast.

[Shaun @ Tru6]

Rensport in Framingham, MA, 508-875-8911

Autosport in Stow, MA, www.autosportengineering.com

both should be able to help you.