Spitfire 1300 Spitfire Compression & Leak Down Results

[dklawson]

My project Spitfire has taken longer than anticipated to get roadworthy and it hit another major delay today.

Off and on (as weather would allow) I've been tinkering with the carb settings, timing, and crankcase ventilation to get the car to the point where I would feel comfortable having my older son drive it. I wasn't getting anywhere so today I did some deeper investigating by performing compression and leak down tests... tests I should have done before buying this thing.

This is a low compression MkIV Spitfire engine. With the engine warm and the throttle held open I got the following compression figures (all in PSI):
1 = 85, 2 = 88, 3 = 82, 4 = 88
Lower than I anticipated but still within 10% of each other.

I moved onto the leak down test. To confirm piston position I removed the valve cover... and found moisture... "sweet moisture". I thought this was curious since the compression tests gave no hint of a blown head gasket.

The leak down test was performed as follows:
Each piston measured at TDC on the firing stroke, 100 PSI in, listening for hissing at the carb, exhaust, pushrod tubes, and radiator.
I got the following results.
Cyl. 1, 85 PSI out, air leakage into the block
Cyl. 2, 75 PSI out, air leakage into the block, air leakage into the coolant
(a steady flow of coolant moved by the air)
Cyl. 3, 52 PSI out, air leakage into the block, air leakage into the intake manifold
Cyl. 4, 85 PSI out, air leakage into the block, air leakage into the intake manifold

The curious thing to me is the leak down test found what is apparently a blown head gasket (or worse yet a crack into the water jacket from something in cylinder #2). Shouldn’t I have found some indication of these problems from the compression test? There is NO apparent oil in the radiator but clearly water has now mixed with the oil based on the corrosion I found on the rocker arms. I obviously have some decisions to make real soon about what to do but I didn’t buy this project car anticipating an engine rebuild to get it on the road.

So this question is moot at this point, but what “would” be a more or less normal compression figure to expect on a low compression 1300?

 

[TR3driver]

Shouldn’t I have found some indication of these problems from the compression test?

Can't help with your other questions Doug (and BTW, you have my sympathy). But a compression test frequently will not disclose smaller leaks, like a cracked cylinder head or wall. Even burnt valves don't always show up, if they have just started to burn. Things are just moving too fast to show, unless the gap is considerable.

 

[jdubois]

Sorry to hear about your troubles. Being in a similar situation myself currently, I definitely feel for you.

So this question is moot at this point, but what “would” be a more or less normal compression figure to expect on a low compression 1300?

The rule of thumb I've always used is 15-20 times the compression ratio. So on a 7.5:1 ratio engine, I'd think you'd want to see between 112-150.

 

[pjsmetana]

Your #s say head gasket all over it. I bet you have a bit of coolant in your oil, and/or oil in your coolant. Although you stated there isn't any, I bet there is at least some.

But I wouldn't worry about that. Since your numbers are all significantly low, I would suggest pulling the head off and doing some checks from there... thus needing a new head gasket anyways.

When the head is off, flip it over and set it level on a towel and pour some gas into the area where the valves are. If the gas leaks out, you have leaky valves. The faster it leaks, the worse it is. Might as well get those fancy new hardend-seat valves so you don't have any problems with modern gas. Well worth it!

With the head off, you might as well take a look at the cylinder walls and the piston rings. Uneven wearing is obvious (looks like its wearing unevenly ) and a sign of needing the replace all your rings and hone the sleeves.

BTW, this is all easy stuff and can actually be done without ever removing the engine. I do, however, suggest taking your pistons to a machine shop to have the rings installed. They will gap them perfectly (or rather no gap at all) and install them on the pistons without having to worry about breaking any (like I did).

I have 3 rules for engine builds:
1, permanent marker does not affect performance and you can write all you want on the engine.
2, If it has a torque specification, use it and follow it to the letter as if it were law.
3, paint the parts while its off.

Sure its a little time consuming, but its also fun, and when your done you can say "I did that", which is worth a lot.

 

[dklawson]

Thanks Pete. However, my approach is going to be to "mooch" a used engine from a friend. I really, really don't want to invest the time or money rebuilding this low compression 1300. It just seems like throwing (more) good money after bad (which is typical of the whole car). If I can't mooch an engine I'd rather buy a used 1500 core and put the money into rebuilding it. I've rebuilt a couple of engines over the years so I appreciate and understand your statement about personal satisfaction. However, the last engine rebuild represented an outlay just under $2k (1275 Cooper-S). This Spitfire is NOT worth that sort of investment.

I did say that I did not see oil in the coolant. However, I am sure there is coolant in the oil as there was antifreeze inside the valve cover. As for the valve leaks, the leak down test made it pretty obvious I've got intake valve leakage on cylinders 3 & 4. None of the cylinders appeared to have leaks on the exhaust... which is where I would expect the leaks to be. Poor tired old thing.

 

[TDHoward]

Sometimes a bad head gasket will function as a "one way valve"
ie allowing pressurized coolant to pass on a "vacuum stroke" then closing on the compression stroke. It'll blow out the bad valve seat and pass the stem seal and viola' coolant under the valve cover. =Water in the oil, but no oil in the coolant, yet.

Valve lap and stem seals, + a head gasket will go a LONG way toward fixing your problems.

While the head is off, oz or two of Marvel Mystery oil in each cylinder to seep down around the pistons to free the stuck rings...

Of course all this is moot if theres a crack in the liner or water passage, but I'm betting tired head and sticky rings. Good luck!

 

[pjsmetana]

While the head is off, oz or two of Marvel Mystery oil in each cylinder to seep down around the pistons to free the stuck rings...

My Compression numbers were pretty bad for a while too... till I did something similar. I sprayed water into the intake while at around 3000rpm. Cleaned the valves and unstuck my rings. Randall and Doc passed this trick onto me about a year ago, and I can pass this on to you too if your interested. Sure saved a whole lot of time and money.

 

[dklawson]

I sprayed water into the intake while at around 3000rpm. Cleaned the valves and unstuck my rings. Randall and Doc passed this trick onto me about a year ago, and I can pass this on to you too if your interested. Sure saved a whole lot of time and money.

I remember that thread. That was about a year ago wasn't it? I'm going to hold off on any fixes until I talk to my friend about the availability of his 1500. Thanks for the continued support.

 

[DrEntropy]

:lol:

Sounds like you're not gonna need the "de-coke water-boarding" technique, Doug. Throwin' money at a 1300 would be kinda sideways if you can find a good used 1500 to go thru.


EDIT: Hey Pete! When ya gonna segue yer butt over here fer that beer?!? :laugh:

 

[TR3driver]

I dunno ... If I recall the scuttlebutt properly (always a risk), the small crank 1300 is generally regarded among the racers as the fast way around the track. Somepin about the stroker engine won't turn as fast, doesn't oil right, etc. (not to mention the stock CR of 7.5:1).

 

[Bob Claffie]

I'm with TR3driver. I would take a 1300 over a 1500 any day. A set of pistons would boost the comp ratio up to a reasonable # and everything after that would be gravy. I didn't notice the year of your Spit but it's possible a 1500 won't mate up to your tranny, depending on the respective years. Bob

 

[dklawson]

My Spitfire currently has the later single-rail gearbox, a 1500 flywheel, and all the later clutch bits. So installing the 1500 won't represent a compatibility issue.

On the other hand, my car/engine is a '72 with the low compression 1300. I don't know if that makes it a small or large crank model. I remember reading some reports that said this combination was one of the slowest Spitfires built... so I'm not really excited about pouring money into this particular engine.

I see it like this... I can take the engine out (I would not do a rebuild/refresh in place) and as a minimum get the block tanked, checked for cracks, honed (if I can get by with the existing pistons... doubtful) get new rings (since I know from the leak down test that they aren't sealing) then get the head redone. The engine has decent oil pressure cold but it drops dangerously low at temperature. As a minimum I'd be looking at a set of bearings and an oil pump IF the crank doesn't need grinding. Of course I also have to get a new gasket set and do some other clean up tasks. If I'm lucky I might get out for $500. On the other hand, my friend's 1500 will be "free". The DR described my situation/decision pretty succinctly above.

This Spitfire has been more project than I anticipated and like all projects it came with surprises and hidden expenses. However, an engine rebuild was not in my original plan or budget (naive me). If I can get my friend's engine for free and swap it out, that is what I'll do. If I am unable to get my friend's 1500 I certainly will revisit the idea of refreshing the 1300. Again, I appreciate all your suggestions and words of support.

 

[billspit]

I'm a little puzzled by what you are calling a low compression 1300. I wasn't aware there were low compression and high compression 1300s imported into the US. I thought only 1500s had a low and high comression engines here. I know if you put a 1300 head on a 1500 you get a very high compression.

Does the "big crank" 1300 have a lower compression than a "small crank" 1300.

 

[dklawson]

I'm a little puzzled by what you are calling a low compression 1300. I wasn't aware there were low compression and high compression 1300s imported into the US.

Sorry, I wasn't trying to confuse the situation. I claim no knowledge of what Spitfire engines were and were not imported to the U.S. I have not studied Spitfire history or evolution.

I am basing my low-compression comments only on what I found online as the Spitfire & GT6 magazine web site.
https://www.triumphspitfire.com/enginenumbers.html
I have an FK series engine which they list as a U.S. issue 1296 with 8:1 compression. I'm comparing those the the FH and FE series engines with 9:1 and 8.5:1 compression respectively.

If you say the FH and FE series engines didn't come to the U.S. I accept that.

 

[Andrew Mace]

FE series did come to the US, for the 1969 and 1970 model years and were slightly detuned version of the FD, small-crank 1300. From the 1971 model year in the US, FK was the "emissions" version of the large-crank engine, and the 1972 model year FK engines introduced the recessed bore and yet lower compression (UE suffixes). They were indeed about the least powerful ever Spitfire engines @ around 48 hp, but they were still pretty torquey. I spent many years occasionally borrowing and enjoying (and maintaining for him) a buddy's '72 MkIV with that low-compression engine...and it was every bit as willing as any other Spitfire engine with a single Stromberg, although maybe not quite as torquey as the long-stroke 1500s.

 

[billspit]

Thanks Doug and Andrew. I have learned something today. Do either of you (or anybody else) know if the reduction in CR in the 1296 was due to pistons or the combustion chamber in the cyl head? I am aware that the 1500 had oodles of part numbers of cyl heads.

I ask because I was able to pick up a set of flat top pistons real cheap off ebay a good while back that I was intending to use for rebuilding a big crank 1296.