> Jensen Healey & Jensen GT Tech > Engine & Transmission > Differences between MkII engine and GT engine? |
> Jensen Healey & Jensen GT Tech > Engine & Transmission > Differences between MkII engine and GT engine? |
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answerman Member
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Hey guys. Considering buying an engine for Ms. Jenavieve. Are there any differences between a MkII 907 and a GT 907 that I need to know about? She currently has her original engine, MkII type (later style with lip style rear seal, not a rope seal). Joe Mazurk has a GT engine available. I know there were some differences with peripherals like air pump and such, but should it be a straight swap otherwise? |
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NigelK Member
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I think it depends what engine was fitted to the GT. Jensen used whatever engines they had available at the time, including A74 (Dellorto), B73, B74, and T75 (Stromberg). According to Ric Calver, all Federal market GTs had the T75 engine, which may also have been fitted to very late JHs. It would be an idea to compare engine numbers between your JH and the GT. I think the main differences between B74 and T75 engines will be emissions / ignition related, and perhaps also the air box setup. Last edited on 09-14-2015 08:31 pm by NigelK |
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answerman Member
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Good information so far. The current engine in her is B74.03.6527. I think the items you mentioned will fall under the "peripherals" I was talking about and won't be included with the engine anyway. I was more worried about core items like the block/head/clutch/tranmission/etc itself since I'll likely be pulling the Strombergs and all the current ignition components from my current engine for transfer to the new one. Consider it a bare T75 engine for the purposes of this question. Long term plan, assuming the new engine is a decent runner in its current condition, is to swap the new engine in and then do a proper rebuild on the old engine as time permits. |
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t4brew Member
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Some of the 907 emission heads had eight air injection ports on the exhaust side where the air injection rail was attached. The GT 907 engine may have these ports. I have seen two 907 emission heads with air injection ports. One still had the original air rail attached and the other had plugs in the air injections ports. If the GT 907 engine you are looking at still has the air rail you may need to find plugs for the air injection ports. Attachment: air-injection-port-small.JPG (Downloaded 192 times) Last edited on 09-14-2015 09:59 pm by t4brew |
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NigelK Member
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A few more thoughts... 1. The water pump and fan setup may be different, as T75 engines had the later viscous shrouded fan and crossflow radiator (this is probably also "peripheral") 2. Check if the GT had A/C - this could mean a different cambelt tensioner and crankshaft (amongst other things) 3. RH engine mountings will be different (in order to make space for the air pump) 4. Valve timing is different for Federal engines after # 10480 Presumably your JH already has the 5-speed Getrag box fitted? If not, the bell-housing will obviously be different on the GT engine too... |
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answerman Member
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Nope, I have the 4-speed. I would assume the bell housing will have to come off of the current engine and transferred. The GT engine has the water pump installed yet (no idea of condition) and the cambelt installed, so the tensioner etc is all there though obviously I'd replace the belt and bearings before swapping. How would the engine mount be different? |
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NigelK Member
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The GT parts manual shows different RH engine mountings and subframe for T75 engined cars. With the T75 engine, the subframe bracket to which the engine mounting is attached is located where the subframe swings upwards from horizontal to sub vertical. On non T75 cars, this bracket is a completely different shape and is mounted halfway up the sub vertical part of the subframe. The engine mountings need to be a different shape as a result. I think these differences were all to create space for the air pump. But there is nothing in the parts manual to indicate anything different in the block casting, so provided you retain the B74 engine mountings you should not have a problem. |
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Brett Gibson JH5 20497 Member
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Mike, a GT engine will bolt right into your JH, water pump is different comes out the side instead of up front like yours, you would need to switch yours onto the GT engine and it also sounds like you would have to use your JH engine mounts, otherwise you are good to go, what is the problem with your original engine ??? and don't forget you would be buying a used engine that if I know Joe would be AS IS, I'm sure he would be honest about it's condition as much as he knows about it but there would be a question mark. Brett |
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answerman Member
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Thanks for the info. Brett, there is nothing wrong with my current engine other than that it is going to turn the odometer over in the next few weeks and I think it may be time for a rebuild. My thinking is that if I am going to do a rebuild, I would rather do it on the original "numbers matching" engine. So, the plan would be to (assuming the new engine can be made to run fairly easily) swap the new engine in and then rebuild the original engine at my leisure for reinstallation later. Though, I went through the service manual last night and the rebuild doesn't look as complicated as I expected, so maybe I am worrying about nothing and can easily get it done this winter. I just don't want to be caught without a running engine next spring, so this was a backup plan. Joe was very clear that the GT engine is "as is". It came from a car with 45,000 miles on it, he has never run it, but it is complete, spins freely, and has plenty of compression according to him. |
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wtberks Member
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On my GT, the engine has the air injection ports, which you can plug, a slightly different oil pump housing, a different water pump. the dreaded air pump, an A/C compressor and no place for the rear engine damper. The oil pump housing has the top mount cut off and a taller one bolted on, presumably to mount a larger alternator. The water outlet from the thermostat also connects to the radiator following a different, less cramped path. The rear damper is missing as the air box fan on the firewall is in the way of where the mount would be in a JH. |
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Screenplay Member
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I'd second Brett on the "e caviat emptor." No need to rehash old stuff but just go in with your eyes wide open. |
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Esprit2 Member
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t4brew wrote:If the GT 907 engine you are looking at still has the air rail you may need to find plugs for the air injection ports.The plugs are 1/8" BSPT, Allen drive. If Delta doesn't have them, then JAE does. |
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Art DeKneef Member
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I'm not sure but I believe there was a discussion on the differences between the MKII engine and the GT/later 907 engine somewhere on the board. All the GT engines I have seen her have had air conditioning, air pump and fittings, different subframe, different water pump and radiator. There might be a couple of other minor differences I don't remember right now. 1. Engine block is the same. The difference in mounting has been mentioned. The passenger side engine mount is different because of the air conditioning compressor. 2. Since your car is a 4-speed you will need to use the bell housing for your current JH. 3. Water pump, fan and radiator are different. You need to use your current water pump and fan on the GT engine. Otherwise you need to swap radiators and then you lose the cooling shroud. 4. You can remove the air pump and fittings. Delta has the plugs. Like Brett mentions, it will fit. You need to take the changed parts of the GT engine off and replace them with your parts. Then reconnect the fittings and electrical and hope it starts and runs. If not just repeat the process in reverse and you can still use the old engine. Also, depending on the age of your current engine, it's possible that the heads on the GT might have larger ports. Given the choice I would probably leave the current engine in the car and rebuild the GT engine instead. |
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Lash Russell Member 
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Gents, Regarding the different engine mounting locations for the GT (and I think on later JH's), was this strictly to accommodate the air pump of for the AC compressor, or both? Thanks, Lash |
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Frank Schwartz Member
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Definitely use your original water pump...the one in the GT has a longer shaft and will not accommodate your belt driven fan...the viscous coupled fan very often does not work well anyhow. Other than plugging the air holes and using a single bend hose on the upper radio connection instead of the crazy S hose, all should be interchangeable. Oh, yes, the GT uses a three row radiator whereas the JH uses a two row radiator...and the GT radiator mounts differently... I have found the tensioner to be identical and I cannot see where you would have trouble replacing it or using the one on it, assuming it will come with it. Just replace the bearings, which is a good practice in the tensioner. If the GT engine is stripped, I think you can pretty much swap it without much trouble using most of your stuff such as the alternator etc.... I have a low mileage (24k) GT engine that I am going to put in a JH which has no compression on #3 and was driven very hard for a long time by the owner with the distributor stuck at 45 degrees of advance. I think it will be easier to replace the engine than to try to repair all the damage he has done. |
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Art DeKneef Member
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Lash, My experience, with my cars, is that the only engine mounting difference is on the passenger side because of the compressor. The engine mounting brackets are different between a non AC car and one that has AC. The driver side bracket is the same. The air pump is located on the driver's side and uses a different bracket for mounting and a different fan belt. |
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Lash Russell Member
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Thanks Art, I was pretty sure of that but glad you confirmed. Lash |
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