Bad Engine

[latinowarrior]

I just found out that the #7 piston is @ 25 PSI. They tell me that I need to rebuild the entire motor, it will cost about $2,500 dollars. I have a 4.1 engine in the car. Q, can they just fix the bad piston or should I go and have the entire motor redone. The car has over 140,000 miles on the meter. HELP

[jupiter57]

I just found out that the #7 piston is @ 25 PSI. They tell me that I need to rebuild the entire motor, it will cost about $2,500 dollars. I have a 4.1 engine in the car. Q, can they just fix the bad piston or should I go and have the entire motor redone. The car has over 140,000 miles on the meter. HELP

That sounds pretty steep for a 4.1, IMO. (Could be that I do all my own work!)

I would check around. If the Caddy is in good shape, if the rebuild has a warranty, and you plan on keeping the car for a good while longer, it may be worth the cost to you.

You may find a shop that is willing to pull just one piston and repair it, but with the work involved in that, it may cost close to a real rebuild.

Check at your local salvage yards, or try CarParts.com for yards & prices in your area.

Here in KY., used engines go for $300 - $600.

[joeb]

low compression could be a bad valve. pulling 1 head is cheaper than a whole motor though. i helped a friend pull both heads on an older car once. i can't remember why we did it. overheating? too long ago. anyway, one of the exhaust valves was missing a pie shaped piece, probably 1/5 of the valve. it seemed to run ok, i recall it had a blowby issue and would fill up the aircleaner with an oil film. maybe pcv issue.

[BodybyFisher]

I was thinking the same thing, low compression does not equate to "let's replace the engine". This could be carbon on a valve, bad valve guide, collapsed valve spring, burned valve, cracked valve. Did they determine what it is? I believe if you add oil to the cylinder, if the compression picks up its the rings.

[latinowarrior]

OK, I'm having low pressure (25 psi) on my #7 cylinder, will I need to replace the motor or just fix the cylinder? HELP Me OUT!!

[Bill K]

After reading the above responces to your original question its seems you may have to help yourself by finding out what is causing the low compression.

Rings?

Valves?

Gasket?

[KHE]

Since the low compression is only on one cylinder, some troubleshooting is in order to determine the cause. It could very well be just a broken valve spring or a burned valve - in that case, just the defective components could be replaced. More information is needed in order to plot a course of action.

[Bruce Nunnally]

The HT4100 was not a great engine reliability-wise. The best I have heard was that if you were very careful on maintenance, and it NEVER overheated, it did okay. And on the bright side it was developed into the 4.5L and 4.9L OHV engines which were quite reliable.

Now, that said, I would have the entire engine rebuilt, if you want to maintain originality. YOu might consider moving to the 4.5L which I think is almost or is a direct swap. THis site: http://remanufactured-engines.com/page11.htm is not pretty, but does have some info on the topic:

I WOULD LIKE TO UPGRADE MY CADILLAC 4.1 ENGINE TO HAVE MORE PERFORMANCE. I HAVE SEEN A 1985 WITH A 350 ENGINE. IS THIS POSSIBLE AND CAN YOU DO SUCH A SWAP? ANY INFORMATION ON THIS WILL BE GREATLY APPRECIATED:

We limit upgrading this engine to a custom version of the 4.5 liter engine for a few different reasons, not the least of which is laws from state to state that consider a complete engine change the removal of legally required anti pollution equipment. (fines)

The other alternatives are also heavy and require a computer change, front end alignment, changing the brake proportioning valve, myriad bracket pulley, plumbing and bracket changes, manifolds, exhaust, etc. In short, if you find someone to do it, add at least a few thousand dollars. We party poopers won't do it at any price. ()

The 4.5 liter engine improves the power situation significantly for not a lot more money and it's difficult to tell the different from the original HT4100 engine other than the power increase.

Having said this, you should know that the design is almost identical to the 4.1 from a reliability standpoint BUT we make over a dozen major changes and improvements to the original engine, whether 4.1 or 4.5. to make it very reliable.

[KHE]

The HT4100 in an '84 Eldorado is a longitudnal engine - the 4100 was produced in both transverse and longitudnal versions whereas the 4.5 was only a transverse engine.

The good news is that all the improved gasketing technologies that were incorporated in the 4.5 and 4.9 engine were also incorporated into the HT4100.