Engine Loss Test

[mcgc0]

I'm still scratching my head over whether I should take the plunge for a top-end overhaul. My 1990 C4 had a loss test about a year ago - (%) 12 / 37 / 24 / 23 / 29 / 11.

I also hear that values like the one's above are not too much to worry about and that many drive around like that (or worse) for years. The engine pulls well and is on the button and sweet. Should I bother with any rebuild cost now? I've been offered a top-end rebuild for £2k (from a well known specialist of many years), but no doubt the usual scenario of more cost on other things will creep in.

Any thoughts..?

Cheers

 

[RLambert]

How many miles has it done ?

If it's not puffing smoke and you are happy with the performance then I wouldn't bother. As you say £2k is just the start and it's more likely to be twice that with all the 'other' stuff they find that is worn out!

 

[mcgc0]

130k miles on the clock but at 94k miles it had an engine rebuild by Tognola (according to the receipts).

No engine smoke at all, and oil consumption slightly more than the litre/3500 miles suggested so not too worried about that.

 

[Dave Wilkinson]

Marcus,

I think it all depends on what you use the car for. I'm in pretty much the same situation with my car but because it's a weekend bit of fun and I don't track it at all, I have no problem with oil loss or usage and the engine seems to run well and pulls strongly I would have a hell of a job convincing myself to spend any large amount of money until it became obvious that it was essential.

If the car is used with a vengeance on track it's probably a different story as the stress levels are likely to make the situation somewhat worse quite rapidly.

The £2K price sounds attractive but I'd be surprised if you got away with the parts being much less than that and, as you said, there's always the dreaded "while we're in there" issues that always seem to escalate out of all control.

I'm a firm believer in the old adage of "If it ain't broke, don't fix it!".

Regards

Dave

 

[mcgc0]

Sound advice Dave. My typical use is the odd weekend (or has been during the winter), but hoping to use more frequently. I had thought of doing the Brands Hatch novice evening just to get to know the car better with view of needing to do the 'Ring' at some point.

I do enjoy a spirited drive to Le Mans every year too! All in all then will probably leave for a while until the engine feels worse or until I have a self-indulgent moment..

 

[Steve Brookes]

The rebuild of my own engine is now finished and I will be soon updating the thread I have running on the subject. I would summarise my own experience as take whatever the initial estimate you have been given, double it and you'll be in about the right ballpark.

The cost goes up because of a lot of other stuff that gets found. Some you can resist but most you can't. Add to this the rapidly increasing costs of genuine 964 parts. For example, I needed a set of rubber intake stacks. Just prior to my rebuild these retailed at £20 + VAT each. On ordering mine Unit 11 were informed that these had just been increased to £40.10 + VAT each. And you need 6 of those! Unfortunately for us, as the parts bins run down, the prices are getting hiked up at an alarming rate. For this reason I believe that the cost of rebuilds are going to increase each year far beyond the rate of inflation.

 

[mcgc0]

Been following your rebuild with interest Steve. Not too far in the future then I might save up the pennies and go for it rather than save myself for the bigger cost hit later on with parts costing even more and more.. Wish I had the time and space to do something like this myself..

Correct me if I'm wrong, but assuming that Tognola did a good job with the engine rebuild, then a top end rebuild will rectify or bring back compression/leak test values to nearly new (as much as it can be in retaining original heads and pistons).

 

[Steve Brookes]

Hi Marcus, I'm not knowledgeable enough to tell you if a top end rebuild would give you back what the engine is losing. My impression is that Tognola are well regarded and I am therefore somewhat surprised that your leakage values are so high when the engine has only done another 36,000 + miles. It would be worth summarising what the engine rebuild included and hopefully someone more knowledgeable than me might be able to comment.

Saying that...my own history shows a top end rebuild at 125K and I've had my full rebuild done at 167K. My decision to have a rebuild was done purely on gut feeling and the desire to have an oil leak free engine. I didn't have compression or leak down tests done. I decided that I wanted to drive her without the worry of the engine letting go in dramatic style. On carrying out the rebuild Unit 11 picked up a lot issues with the previous rebuild. They were not impressed with the original work that had been done.

 

[mcgc0]

Thanks Steve, maybe I'm worrying about nothing then and another leak down test this year will suggest the rate of change (if any).

Tognola did a full job (and some) and I've attached the receipt for interest. Look about right?

 

[turbo jonny]

Who did the tests ? I would not put much store by them unless both compression & leakdown tests were done by
someone as experienced as Unit 911. For example I asked an OPC to do these tests a few years ago and it was a complete farce !

 

[Steve Brookes]

ORIGINAL: mcgc0

Thanks Steve, maybe I'm worrying about nothing then and another leak down test this year will suggest the rate of change (if any).

Tognola did a full job (and some) and I've attached the receipt for interest. Look about right?

It looks quite a strange list to me, especially when comparing it to my own. While gasket kits are listed which would be needed for the re-seal, there's no mention of valve guides, springs, valve re-seating, piston rings, chains and tensioners. These were all part of the top end rebuild done on mine. The references on your list to 'S/H crank' and 'S/H rods' suggest to me that the engine developed a problem with the bottom end and the rebuild was done to fix it. I also presume that S/H refers to them using second hand parts in some cases.

So in answer to your original question, my limited knowledge makes me think that it's not had a proper top end rebuild and it could therefore benefit from having one done.

 

[mcgc0]

Thanks Steve, what I don't know exactly is what a 'menu-based' rebuild (top-end) should include in terms of parts and replacements. Is there somewhere you can point me to that would indicate or detail this - somewhere in renlist maybe? I may want to add or 'upgrade' some of those same parts (e.g. coated 993 cylinder bolts instead of the earlier ones etc).

 

[Steve Brookes]

A menu rebuild will be specific to which specialist you use. Mine done by Unit 11 included:

Top end sealing kit
Piston rings
Cam chains
Valve guides
Dialever Studs (the 993 type)
Oil through pipes
Labour

See the most recent post on my engine rebuild thread for a list of all the extras I needed for this (bearing in mind that I also had the bottom end done).

 

[mcgc0]

Coming to the conclusion that while a leak down test is not always conclusive and comes with some subjective viewpoints (unless values are really lousy and able to be repeated), the previous engine rebuild I had probably wasn't all was what it could have been.

Think then I will chase up the contents of my top-end rebuild offer and make sure that what Unit 11 included is al least implied as well.

 

[RLambert]

Yes, the receipt is missing all the top end rebuild parts it would have needed. And as it isn't showing piston rings so as Steve says it seems to be a cheap(ish) fix it job but then at least you should have confidence that the bottom end is sound.

From what you have said the engine seems fine and you will find the majority of 911 engines driving around out there have similar leak down figures. And don't worry about it letting go as it won't, it will just lose power slowly over time.

Spend your money on some decent suspension and once you know how to drive it properly then you can think about more power. []

 

[mcgc0]

All good advice - thanks. Just that a half-price offer for the top-end rebuild as a condition of my purchase from RPM is tempting and will buy peace of mind for many, many 000's of miles. However, I am just bowled over by such a brilliantly designed and hand-built engine that probably left as is I'll be grinning for a long time yet. It's so free revving with the RS clutch and flywheel the other end..!

Eibach suspension and handles beautifully at the moment, but a day at Centre of Gravity is a must do for me this year, as is a live engine remap.

 

[mcgc0]

On completion of a top-end rebuild would some sort of 'running-in' be required? I'm not expecting to gun it straight away, just wondering if there are any limitations or other considerations..

 

[Steve Brookes]

ORIGINAL: mcgc0

On completion of a top-end rebuild would some sort of 'running-in' be required? I'm not expecting to gun it straight away, just wondering if there are any limitations or other considerations..

I've been advised to keep rpm below 5,000 for the first 1,000 miles and then go back for an oil change and valve clearance check/adjust.

 

[carrerasport]

After studying the reciept i am in agreement with the majority on here in that the work was done to fix a problem and the owner just couldnt afford the extra bits to make it into a rebuild/refresh as well(shame because it would have been cheap really).
one thing i disagree with is the fact that people are saying your not doing any damage continuing to run the engine with your poor leakdown figures,If the figures are accurate then the fact that they are not even is a cause for alarm as this is not usual,i have seen plenty of 100,000 plus cars with good even figures closer to 20% across the board. approaching 30 plus percent and the chances are that something is amiss even if it cant be felt,and if its left it can destroy the valve seats and valves if its the guide which is worn or if its the piston rings ,they can damage the bore and the piston if left to get very thin at the ends and they break up into multiple pieces.oil consumption is a factor, but that piston ring is not the one usually found to have the most significant wear,its allways the compression rings 1 and 2 (oil ring being no 3).
I would be considering getting one more leakdown check carried out and planning to act on it if the figures are repeated.Its an expensive job to do in its basic form and you dont want to compound the problem by running the engine on past the point at which it should receive attention.Also beware of deals struck to do it on the cheap as you may not be there to see any corners that might be cut because you will never be in a position to examine it! They may not give it their best attention because there is no money in the job for them.
best of luck C

 

[mcgc0]

Interesting feedback and comments - thanks. Easy then to conclude that the cylinder with the higher leak down value may be the piston, rings or valves/guides that are 'misbehaving' the most - others being less of an issue. Regardless it's a to-do for me in the next few months.

I have asked for a rebuild list of items that are included and am intending to get involved where I can. As anywhere there is always an element of trust, and I can't imagine that it would be in a workshop's (or engineer's) interest to put at risk a reputation that has been built up in the 911 community.

Once I get that list I might post up.

Cheers